Wednesday, November 25, 2009

Wet but Calm

November 25, 2009
5:35 P.M.

Hey guys! Thanksgiving is less than a day away! I am soooooooo excited. Man... I haven't tasted that creamy mash potatoes that melt in your mouth infused with a concoction of gravy and stuffing for over a year. And the turkey... I just took a look at it. It's huge. And I'm going to eat as much as I can. We are also hosting an apple cider pressing party up at our beachhouse on Whidbey Island, where we will cut and grind apples and them press them to make apple cider. Let me know if you want some! I'm sure we will have way too much. It's great stuff and it is really fun to make too.

These two images show the expected rain from now to 4 A.M. tomorrow and then that time to 4 P.M. As the title says, the weather will be fairly uneventful this Thanksgiving in terms of wind and general storminess, but we should get a good shot of light but steady rain starting tonight and lasting into early Friday. All this rain is due to a front stalling over the area. Where most fronts sweep right on through, this front will have little eastward progress (storms go from west to east in our neck of the woods). Due to that, we could see an inch of rain throughout the lowlands, and the Skokomish could see some minor flooding. Still, the mountains will not see the prodigal widespread 5-10 inch amounts they were seeing with some of the systems earlier this November because the winds in the upper atmosphere will not be that strong, which means that there will not be much orographic enhancement on the mountain peaks. Of course, that means there won't be much of a rain shadow effect in locales like Sequim either. Everybody will be wet. And the snow levels will be high too, which is great news for travelers across the pass but bad news for us skiers.

I have to go eat dinner but I will be out of town until Sunday. Apart from some rain on Saturday the forecast looks pretty uneventful. Have a FANTASTIC Thanksgiving and thanks for reading. :)
Charlie

Tuesday, November 24, 2009

Benign Weather Week Ahead

November 24, 2009
4:37 P.M

Hey guys. Sorry for not making an update earlier... I had tons of homework and was studying for multiple large tests. Although I still have to do some stuff tonight, it is looking like a less strenous day tomorrow which means I'm not currently swamped at the moment. I am pretty tired though. I can't wait for Thanksgiving, which is my second favorite (and Christmas isn't even my favorite, its like Winter Break before Christmas that I absolutely adore) holiday (although technically that isn't really a holiday, in which case Thanksgiving would come in first (and sorry for all the parentheses btw)). Thanksgiving is my favorite Holiday for several reasons. First of all, there is delicious food. What is your favorite Thanksgiving dish? I personally die for a mix of stuffing, gravy, and mash potatoes. Write your answer below as a comment to this post!

I also love Thanksgiving because it is, on average, the stormiest holiday of the year. Although we will have rather pleasant weather this time around, there have been many a stormy Thanksgiving, and many of those have been celebrated in the dark, which really makes you thankful you have a roof over your head. Maybe Mother Nature is playing tricks on us. Such a situation occurred on Thanksgiving 1983.


The image above is taken from Wolf Read's "The Storm King" website, a website I highly recommend for anybody interested in severe weather events, particularly windstorms, in the Pacific Northwest. It shows peak gusts at the Sea-Tac airport for each day during the entire month of November 1983, which was really stormy in general. For the "granddaddy" of them all, the Thanksgiving storm made landfall just north of Hoquiam as a 972 millibar low. It delivered a powerful gale to the Puget Sound region with a 62 mile per hour gust at Sea-Tac. As I'm sure you can imagine, this type of wind, combined with the saturated soil I'm sure was present at the time from all of the previous storms, toppled trees and power lines across the region, making for many a cold turkey. Don't get me wrong, I love charred barbecue - it makes me feel like a true Northwesterner -, which is what many families resorted to during the time, but I like a fresh turkey out of an electrically-heated oven more. I'm not that tough.

This week will bring fairly benign weather to the region. Fronts will arrive Thanksgiving day and Saturday with showers in between before we see some drier weather setting up by next Monday. Have a good one folks!
Charlie

Sunday, November 22, 2009

So... What Happened?

November 22, 2009
10:59 A.M.

Good morning everybody. Many of you guys weren't up late at night like me, but if you were, I'm sure you'd be asking the same question... "where is the wind?"

Well, the surface low, instead of taking a track towards the central Washington coast like the models showed, took a track towards Astoria. This southern track put us further from the low which gave us less wind and put the Olympia/Southwest Interior area right under the low, where there is also a weak pressure gradient and not much wind. Why was there this short term forecast failure? Simply because of one thing. We don't have a coastal radar. If we did, we would not have this problem. All of the high wind warnings that were put up would either be wind advisories or nothing at all, and devoted weather maniacs like me would have actually fallen asleep instead of staying of late to see if the winds were going to come.

On the plus side, one part of the forecast went very well. There was tons of snow in the mountains! More on that later... I g2g

Saturday, November 21, 2009

Update on Surface Low

November 21, 2009
10:07 P.M.
Hey everybody. I just got back from eating some delicious Indian food so I thought I'd make an update on the forecast as far as winds are concerned for tonight.


Here is the water vapor imagery for . This satellite shot shows the amount of water vapor in the atmosphere. Notice the "dry slot" behind the storm headed towards us. A pronounced dry slot is a telltale sign of an intense low pressure system or one that is still developing. Even when the storm is not visible on the infared satellite, a dry slot can often be observed on the water vapor one.


Here is the infared satellite. In the past few hours, a "bent back occlusion" has developed, which is where the occluded front wraps around the low pressure center. This is also conductive of a vigorous and intensifying low pressure system.
I really can't give a straight forecast (a coastal radar would really help here!) but I don't think the Seattle area will be too windy. Still, we have a wind advisory from midnight till 10 A.M. tommorow I think for gusts up to 45 miles per hour. The southwest interior and coast still have high wind warnings. Also, something I forgot to mention earlier was that this storm will bring a very strong westerly surge of wind down the Strait of Juan de Fuca after it passes early Sunday. Expect winds up to 70 miles per hour there as well.

Charlie

An Intense Low and SNOW!!!

November 21, 2009
1:38 P.M.

Look at the graphic above. It shows the track of the vigorous low I was talking about in earlier posts. This low looks like it will not bring high winds to our area, but the coast and southwest interior could get slammed.

Usually we don't see winds as strong as forecasted (gusts to 70 miles per hour) with lows this deep (this low is only 990 millibars). Winds, however, are not determined by the absolute barometric minimum of the low. Rather, they are determined by the gradient of low pressure. This is a small-scale, surface low pressure system that will still be in the development phase when it comes ashore. All these factors combine to make a very steep pressure gradient. I would not be surprised in the slightest to see a gust to 90 miles per hour in one particular spot - Naselle Ridge in the SW coastal mountains. This place commonly receives high winds, and a similar (albeit much stronger) event on November 3, 1958 gave it a 161 mile per hour gust. Go to http://www.climate.washington.edu/stormking/November1958.html for more information on this storm. The Seattle area should not see strong winds from this storm.
Another aspect of this storm is that it will bring tons of snow to the mountains! Take a look at the 4km mm5-gfs mesoscale model. Amounts of 30-40 inches are seen throughout the Olympics and amounts of 2-3 feet are seen in the Cascades, with even even higher amounts at higher elevations like Mt. Baker and Mt. Rainier.
Even Seattle will see a fair amount of rain from from this storm. From 4 P.M. Saturday to 4 P.M. Sunday, I'd expect an inch of rain here in Seattle, and the rain will be heavy at times tonight. The coast will see higher amounts, with local amounts up to 4 inches possible.
After this, we will get into a MUCH more benign weather pattern with only a few weak systems approaching the NW. One will clip the area Monday and showers will persist through Thursday. After that, Thanksgiving weekend looks completely dry! I'm not too happy about that but I bet a lot of other people are. After getting all the new snow we should pick up in the next day and the additional stuff during mid-week, the weekend should make for some fantastic skiing in the mountains. I'm definitely going to try to check that out. :)

Have a good weekend,
Charlie

Friday, November 20, 2009

Calming Down a Little

November 20, 2009
3:44 P.M.

Hey everybody! Many of my devoted Garfield High School following saw me in the Messenger, the school newspaper today. I'm truly humbled to have had such a great article written about me and to have been given the chance to show something I have started with the rest of the community. Thank you so much Lisa! It was truly wonderful working with you on this article. Now, if you could get me a weather forecasting spot on the Messenger... just kidding. :) I wouldn't infiltrate on them like that. Besides, the Messenger comes out like every 2-3 weeks. I'd need a lot of skill and a ton of luck to get a forecast even partially right that far out. Often times, skill would not be involved at all.

Let's get down to business. There are currently some showers off the coast that are coming westward now. We will see some showers throughout the evening, particularly concentrated around South Everett as a convergence zone should set up there. The mountains will see a little more snow, with higher amounts, possibly up to one foot if the convergence zone really gets going, around Stevens Pass, which is at the same latitude where most of the precipitation will be occuring back in places like Mukilteo. It is also currently a little breezy but these winds will die down tonight. All in all, a few showers throughout the evening, especially north, with winds dying down

I'm still looking at that low on Saturday. I'm not sure if I mentioned it here - I know i did on Cliff Mass' blog - but that low, at least from a cyclogenesis point of view, looks fairly potent. Models show it undergoing rapid intensification as it approaches our coast, and while it doesn't look to be very deep, it could have an intense pressure gradient. The big question is where it is located. The NAM model brings it south by Astoria but the GFS (usually a little more accurate) brings it north by Grays harbor and to our north which would result in strong winds for us. So stay tuned. Either way, the mountains look to get a good shot of snow.

Sunday we will have showers in between systems and Monday another system will come rolling through. Tuesday through Thursday look a little wet but fairly dry by recent comparison, and Friday actually does look dry! Some more tranquil weather looks like it is headed our way.
Charlie

Wednesday, November 18, 2009

Olympics about to be hammered... and more snow for the Cascades

November 18, 2009
3:47 P.M.


Hello everybody! The rain from the approaching front has started falling around the sound, and, as I and every single news station around Seattle has been forecasting, this storm is going to be a wet one. Take a look at the precipitation graphic for the next 24 hours (ending at 4 P.M. tomorrow). There is a large area of 5-10 inch amounts of rain in the Olympics. Thankfully, although this is serious, there have been bigger Pineapple Express events, and the freezing levels with this one will not nearly be as high. Some Pineapple Express events have freezing levels around 11,000 feet. This one is looking like it will boast freezing levels of around 5,000 feet or so, which is great news for both the rivers and skiers alike.


What is exactly causing this pattern for us? The answer, on one aspect, is fairly straightforward; we have a strong jet stream thrusting powerful systems into our area every couple days or so. A more specific reason why we have seen all this stormy weather and rain though has been the fact that a baroclinic band has been stalled over us. Remember the "firehose" reference I made in one of my earlier posts? That is what the baroclinic band is. It is a steep temperature gradient along which precipitation occurs and atmospheric "waves" of varying strength ripple upon. It is these waves that bring us periods of enhanced rainfall, and, to a greater extent, wind.


One thing that sets these baroclinic bands apart from other storm patterns is that they usually remain nearly stationary over the area for long periods of time. While most fronts swing through after 6-12 hours, baroclinic bands associated with Pineapple Express events have been known to stay over the area for 24 to even as much as 48 hours! Combine that with the extraordinarly high freezing levels that are usually associated with Pineapple Expresses (thankfully not as much for this one), the heavy rainfall (since the air is tropical in origin, it is more moist), and the strong winds aloft (which enhance rainfall totals on mountain slopes, and consequently, limit it on leeward slopes due to rain shadowing), stalled baroclinic bands often result in extreme flooding for the area. Thankfully, the case is not so here (although we will see some minor flooding, perhaps even moderate flooding on the Skokomish).


The mountains have a winter storm watch for 1-3 FEET of snow over 4,000 feet, with higher amounts in the northern Cascades. It would seem that Snoqualmie Pass, located at an elevation of 3,000 feet, would only see rain. However, an easterly flow through the passes (remember, since the low pressure is offshore, winds flow to it (east to west in our area across the passes)) will keep temperatures there at or even slightly below freezing, resulting in mainly snow there, maybe occasionally mixed with rain. This will be heavy, wet snow too, which isn't quite that good for a powder day but is wonderful when trying to build a substantial base early in the season.


Winds will also be high on the coast and north interior. We have high wind warnings there with gusts to 80 on the coast and to 70 on the north interior. Here in Seattle, we have a lesser wind advisory as winds will gust to 45 miles per hour. The wind will come in two phases - the first phase is occuring now and is associated with a ~975 mb low headed up to the Queen Charlottes. The winds from this will die down later tonight at around midnight after peaking in the late evening hours. The winds from the second phase will be associated with a surface low that will track up the Washington coast into northern Vancouver Island. If it was deeper, there would be the potential for some serious winds since it is so much closer, but it doesn't look to be too deep, and it looks to loose energy rapidly as it heads north along our coastline.



There is a possible storm of interest Sunday as moisture from a decaying front over the north Pacific interacts with a powerful jet stream off of our coast and spins up an intense area of low pressure. However, the low pressure does two things as it approaches us: 1.) It slows down and rapidly decays, and 2.) it heads to our south (weaker pressure gradients and winds are found on the northern side of extratropical storms in the northern hemisphere). In any event, the mountains will get a decent shot of snow with this storm.

Models show some more rain over the area Sunday. After that, we dry out for a couple days! Models show some rain returning after Thanksgiving but there is nothing of note yet.

I'll keep you posted.

Charlie

Oh! And PLEASE give me any suggestions or tips! This really is an ongoing project and if there is something that you think could be improved I would love to hear it. A shout out to Vinsy Szeto for doing just that. And thanks for reading! I'm glad I can share my passion with so many people.

Tuesday, November 17, 2009

More Rain and Wind

November 17, 2009
9:08 P.M.

I tend to either get a lot of things accomplished during the month of November or not very many things at all. The distinction between the two lies in one thing; weather. When it's sunny outside, I just want to go outside and play, or I can't concentrate because I'm desperately looking for something interesting in the models so I don't die of boredom. But when there is a big storm headed our way, I can't concentrate at all (for obvious reasons). Looking at this storm slated for late Wednesday into early Friday, I think I will be able to get a lot of work done and work productively. It will definitely keep me inside, but it doesn't look so strong that all I'll be doing is looking at wind observations and not reading about Henry Clay and the American System. Rain is always huge when it comes to studying and really makes it or breaks it; if there is a strong, steady rain throughout the day, trust me, you'll get a lot of work done. I know I have.

This storm looks to be very strong, with heavy precipitation (5-10 inches Olympics, 3-6 inches North Cascades) once again in the mountains and moderate precipiation in the lowlands (about an inch). There is a bit of a dilemma for the forecast; one American model, the NAM, which is generally a little less accurate, brings a fair amount of rain to the our area, with 1-2 inches in the Puget Sound lowlands but only 3-6 in the Olympics and less than that in the Northern Cascades. The GFS, however, brings about a half inch of rain to the area, but much heavier rain to the SW slopes of the Olympic mountains, where the stalled out front (called the "baroclinic band" in meteorology) will be located.

In either event, high winds will occur on the coast, with gusts to 70 there, and in the north interior, with gusts to 60 there. Again, the Seattle area will be spared for the most part but we will still see gusts in the 30-40 mile per hour range.

It looks right now like we will see another storm Saturday and another one Monday, but these don't look to be too major. I have to read up on some early American literature right now but I'll have a more meteorological forecast discussion tomorrow.
Have a good night!
Charlie

Monday, November 16, 2009

Quick Update - Winds not looking as strong

November 16, 2009
8:41 P.M.


I didn't blurt it out yesterday (maybe I should have), but I was a little skeptical about the forecast when they called for a major windstorm in the Puget Sound region. First of all, the models were not locking on any one situation. Second, there looked to be another low center partially developing. When more than one low pressure center forms, it is not good for storm development.


Now, the low looks weaker and further north. While we will still get windy, we will NOT see winds as bad as originally feared; I'd expect something on par with last night.


In the meanwhile, look at the water vapor imagery of the storm off of our coast. It is very impressive.

I have a lot of homework to do so I can't really talk much now, but high winds are still expected on the coast, with some headlands in Oregon perhaps receiving gusts as high as 100 miles per hour tonight. While I'm sure many of my fellow weather enthusiasts are dismayed that the models aren't showing the storm to be major, the weather pattern throughout this week looks to be active. After all, it is November. Enjoy the wind and rain tonight and stay safe!

Charlie

Sunday, November 15, 2009

Woohoo!

November 15, 2009
6:01 P.M.

I've been having a lot of trouble getting homework accomplished today and focusing in general because I've had my eyes on two things. And they are both weather related (of course).

First of all, remember how I was talking about how if you brought that band of rain that was stalled over the Olympics just a little bit further south, we could get heavy rain in Seattle? Well that is what the forecast models are showing now. They still show prodigal amounts of rain in the mountains, especially the Olympics, with some areas receiving over 10 inches in a 24 hour period, but the rain there is actually looking to be lighter than what was previously forecasted. Seattle, on the other hand, which was looking like it would receive practically nothing as the "Pineapple Express" stalled over the Olympics, now looks like it may pick up as much as three inches before this series of storms is over.

But the biggest story is the wind. There are two storms that will bring very windy conditions to the area, and the second one could be a major windstorm.

I've been watching the models over the past few days, and I've had my eye on that second low pressure system that develops and slams into south Vancouver Island. There is still a bit of inconsistency regarding that system, but it definitely looks like a possibility. I'll talk about that later
video
Let's first start out with the first system. This system actually bears some resemblence to the December 2007 Great Coastal Gale. In that storm, a huge Pineapple Express developed and stalled over the area, bring copious amounts of rain to the mountains and causing the Chehalis River to crest at all time flood levels. Some places on the southern Washington coastal range saw in excess of 15 inches of rain in one day! That's about 40 % of Seattle's annual rainfall! As amazing as the rainfall totals with this storm were, the wind was more amazing. This storm prompted the National Weather Service to post their first ever "Hurricane Force Wind Warning," a warning used when sustained winds or frequent gusts of above 74 miles per hour are expected. And it held true - the Northwestern Oregon and Southeastern Washington coasts experienced amazing winds. There were numerous stations with gusts of 130 miles per hour. Waves on the ocean were as high as 70 feet. See the youtube video for some footage some guy took of the storm event on the Oregon coast. It is absolutely incredible.


This storm doesn't look to be that severe by any means, but, at least to my ameteur meteorological skills, there seem to be many parallels. The diagram above shows very strong sustained winds of 40 knots or more over the waters off the Washington coast (1 A.M. Monday). Notice the abrupt ending in the winds off of Cape Flattery. That is where the front passes through. However, Pineapple Expresses don't quite "pass through" like other fronts. The best way to compare them is to a huge firehose relentlessly spraying the northwest. And as long as the front and rain are over us, the winds will be too.



The front will gradually shift south through Washington before stalling on the north central Oregon coast. Here, it will re-energize as the surface low interacts with it. Look at how strong the winds become in a matter of hours! The above diagrams (at 4 P.M. Monday and 10 P.M. Monday) show just that. It's not very often you see those patches of white on the forecast models.

In the meantime, it will be raining hard here and in the mountains. The Olympics could get 10-20 inches of rain, and the Skokomish will have to be watched for major flooding. The North Cascades will also get hammered, though with somewhat lesser amounts. The Central Cascades look to escape the brunt of the storm as the "firehose" will be positioned to the north of them, and the Green River shouldn't have any problems.

Another interesting thing to note is the amount of lowland rain. As I previously stated, things are now looking a lot wetter for the lowlands. One model shows 24 hour amounts of 3-6 inches in the lowlands. Others, however, do not show that much precipitation. I will see if I can make an update later tonight as the new models come out on how much precipitation we will see and if we will get urban flooding here in Seattle.

And oh boy... here's the big one.


Current models show a 973 mb low tracking into south-central Vancouver Island. This guy has the potential to bring strong and damaging winds to the Puget Sound area. Often times, a good measurer of a storm's wind velocity in a given area is the pressure gradient between two parts of it. For example, the models are forecasting the pressure gradient between Portland and Bellingham to peak at around 16 millibars, which means that the pressure in Bellingham would be 16 millibars lower than the pressure in Portland. Wind flows from high pressure to low pressure, so we could see very strong southerly winds in the Puget Sound Lowlands. This storm would not be as strong as the Hanukkah Eve Storm of 2006 (that storm had a pressure gradient of 23.2 between Portland and Bellingham!) but it would be strong nonetheless. A HIGH WIND WATCH is currently in effect for our area for this storm, saying that sustained winds of 40 mph with gusts to 60 could occur. The coast and north interior have a HIGH WIND WARNING which means that the National Weather Service is fairly certain that they are going to get high winds. Gusts there could reach 70 miles per hour, with some 80s on the coast. I wouldn't be surprised to see a 90 or break the triple digits there either.

Stay warm, stock up on batteries and gas, and don't stand under any tall trees!
Charlie

Saturday, November 14, 2009

Updated Pineapple Express Forecast + Snow to Surprisingly Low Elevations

November 14, 2009
9:54 A.M.

In a previous post I mentioned the possibility for snow at some of the higher elevations. And guess what? We saw some! Look at this picture from North Bend by Kathy Hyland from KOMO4 News. North Bend is at an elevation of approximately 1,000 feet, and they saw sticking snow. A pretty cool Friday the 13th present from Mother Nature, if you ask me. Other mixes of frozen precipitation including snow, graupel, and even true hail (an official spotter reported it up to a 1/2 inch in diameter) along with thunder and lightning were spotted with a vigorous convergence zone over north King and south Snohomish counties.

The models have actually been remarkably consistent with the major Pineapple express event coming up, showing over 10 inches of rain in a 24 hour period from 4 A.M Monday to 4 A.M. Tuesday in some places on the SW-facing slopes of the Southern Olympics. What most models are suggesting is that the stream of moisture will start out centered on the central Vancouver Island area before gradually shifting to the southern part as well as the Olympics and stalling for a while there, then going south through Washington and gradually fizzing out. The north Cascades will see a lot less precipitation, while the Central Cascades may get nary an inch. For Seattle, it will be a close call. While models have been consistent in bringing tons of rain to the Olympics, they have not been bringing much, if any, rain to Seattle before the front swings through. However, bring that front a little bit to the southeast and we could be talking about much more rain for the area. Stay tuned.
Charlie

Tuesday, November 10, 2009

Flooding Next Week?

November 10, 2009
9:53 P.M.

November is a unique month in that the weather changes very rapidly throughout the course of it. The beginning of November is not notoriously stormy; yes, it is usually moderately wet, but there are stormier periods of the year. By the end of November, though, we have reached the stormiest part of the wet season. The last week of November is, on average, the stormiest week of the whole year for the Pacific Northwest. After that week, things usually settle down a tiny bit but remain fairly constant in terms of storminess up until February or so.

The upcoming week looks fairly wet, but not a soaker. We saw a weak system come through tonight, and we will see some continued showers tomorrow, although many people could see no rain. Thursday we will see a continued threat of showers, but most of them will end in the afternoon.

Things start to get a little interesting Thursday night. A COLD system - the coldest we have seen since last spring - will drop down over the area from the north, exiting on the day Friday. This system will bring dramatically lower snow levels to the area, with snow a certainty above 1,500 feet. The thing I am really watching closely is the potential for some lowland snow (yeah that's right I said lowland snow) Friday afternoon and evening. After the front passes, a Puget Sound Convergence Zone will form. As of now, it is expected to first form by the northern Snohomish county border line before sliding south to Seattle where it will fizzle and die out. The atmosphere will be very unstable with this zone, and thunderstorms are a possibility. With thunderstorms and intense precipitation, snow levels can often be temporarily lowered to the surface. All in all, I am NOT expecting any major accumulations in Seattle proper. If we do get any accumulations, it will be in the foothills. It is very early still and very VERY hard to pinpoint convergence zone events, particularily ones where snow is involved, but I'll keep you posted on details if things change.

The big story I'm looking at right now is the potential for some flooding on the area rivers next week. Models have been fairly consistent with the idea of bringing heavy precipitation to our area early next week. This corresponds to an ongoing MJO (Madden-Julian Oscillation) event. An MJO is basically a pattern of equatorial rainfall traveling around the planet. When it gets to a certain stage, the Pacific Northwest often gets "Pineapple Expresses" and flooding. That certain stage would occur next week, which lines up perfectly with what the models are predicting precipitation wise. The details are still fuzzy, but at this point, heavy rains look probable for Vancouver Island, the Olympics, and the North Cascades. The lowlands also look like they will receive a lot of precipitation as well. As the details become clearer, I will relay them to you. If you know of any people who live on a floodplain, now is a good time to let them know that a Pineapple Express event is possible.
Thanks for reading! It means a lot.
Charlie

Saturday, November 7, 2009

Instability

November 7, 2009
7:16 P.M.

What is instability? I often mention instability as the cause of post-frontal showers after the cold front of a storm system has passed in the PacNW, but what does it really mean for the atmosphere to be unstable? It means that the atmosphere has a steep temperature gradient. Our surface air is relatively mild; it comes straight off the Pacific Ocean in most cases after the passage of a cold front. However, the upper air levels vary considerably from warm sector to cold sector. In the warm sector (after the warm front and before the cold front), tropical air aloft and the surface (although moderated by the Pacific) dominates. In the cold sector (after the cold front), the air aloft is VERY cold but is moderated at the surface by the Pacific. This creates a steep temperature gradient which allows for these showers to pop up.


One thing that shows how the temperatures aloft can vary much more than those at the surface is the snow level in the warm and cold sectors. It is not uncommon for snow levels to shoot up to 7,000 feet during the warm sector, even if the temperature in Seattle is 51 degrees. The following day, after the front has passed, the temperature in Seattle could by 49 degrees, only two degrees cooler, but the snow level may be as low as 3,000 feet. And, the heavier showers associated with instability can often bring the snow level even lower both because they release cold air from the atmosphere in their downdraft and the larger, heavier snowflakes have less time to melt.

The above illustration demostrates how clouds are formed. When updrafts bring a parcel of warm air into the cooler air above it, the parcel expands, cools, and condenses, since atmospheric pressure at higher elevations is lower. As it rises, the air around it becomes saturated with water vapor, as cooler temperatures cannot hold as much water vapor (100% humidity at the North Pole and 100% humidity at Bangkok are NOT the same humidity!). When the air cannot hold any more vapor, the cloud as we see it is formed because the water vapor condenses into droplets. If you have a steeper gradient, you have more clouds and condensation, and therefore more showers.


The reason why there are so many showers and sunbreaks is because wherever air is rising it must also be sinking. When air sinks, it warms and dries, creating clear skies. These clouds are almost exclusively cumulus, cumulus congustus (towering cumulus), or cumulonimbus (raining cumulus, often including thunder).

Hopefully that clears some stuff up for you. The reason the East Coast doesn't get these in the winter is because they have cold ground and cold air aloft, resulting in less of a pressure gradient, and therefore less convection currents (warm air rises) and less showers. However, they do have the Gulf of Mexico and arctic air both at upper levels and the surface that surges down from Canada in the in the spring months, creating mammoth thunderstorms and tornados with winds over 300 miles per hour! I'll talk about that some other time. We get nothing like that, although check out the picture of a funnel cloud over Enumclaw Friday afternoon taken by Tyson Gamblin! That is an impressive-looking funnel cloud. Usually you see wimpy ones over here, not ones like that!

Regarding the forecast for the next couple days, we will see a continued threat of showers tonight and Sunday, but the threat will decrease somewhat. Monday will see a short period of heavy rain as a front passes through. Similar fronts will pass through Tuesday night and Friday. With these fronts, rainfall rates will be rather heavy but the fronts will be fast and not stick around for long. After the fronts we will see more showers. Some of these could be quite powerful. It's hard to predict the strength of these showers days in advance but I'll let you know if we are looking at anything serious as far as a threat of thunderstorms goes.

Or maybe you'll hear it instead. :)

Friday, November 6, 2009

Thunderstorms and a Frank Discussion on Hail vs. Snow

November 6, 2009
5:48 P.M.

All I can say is WOW!!! Unless you've been living in a cave the last 20 hours or so you have no doubt noticed the intense precipitation that has been bombarding the area in the form of heavy showers and thunderstorms.

The radar image above was shot at 11:40 P.M. I was excited about having little homework to do last night and, after brushing my teeth, organizing my binder, and taking a shower, I was in bed by 10 P.M. and fell right asleep. All the sudden, I wake up to heavy rain and wind at 11:50 and a bolt of lightning a quarter of a mile away scares me s***less. Shaken but not stirred, I took a few minutes to stare out the window, admiring the power of nature. I promptly fell asleep shortly afterward. However, I was awakened again by another intense shower at 2:20. Even my mom was excited and rushed to my bed to see if I was awake because she knew that I would love to see the storm. Of course, I was already awake. I looked out the window and contemplated for a short while more before falling asleep again. When I woke up for the last time, at 7:00, it was because of my alarm clock, but if my alarm clock had failed to ring, I would have been awakened anyway by a bolt of lightning that lit up my peripheral vision and I calculated to be less than a half mile away. Talking to a teacher at GHS, she said that that a car behind her at a stoplight was struck by lightning. I also heard that God had spilled his wrath upon the Franklin Quakers in this same medium.
For the rest of the day, we saw more sunbreaks than showers as the atmosphere stabilized somewhat and we were partially rain-shadowed by the Olympics. However, as I type this, a new band of showers has drifted ashore, and there will be thunderstorms embedded in these.
Meanwhile, the coast is continuing to get pounded by huge waves. Waves in excess of 30 feet will continue to crash upon the coast tonight before gradually subsiding tomorrow to the meager height of 25 feet. It will be Friday before we see them approach 10 feet.

Abe Stephenson asked me about hail and snow. His specific question was "when we get hail how close is that to getting snow?? are they related in any way? or is it more like the difference between rain and snow.."
Well Abe, we first have to realize that the two are formed in fundamentally different ways. With hail, supercooled water droplets condense on an object, such as a speck of dust. When this supercooled (below 32 degrees Farenheit) water condenses on the object, it freezes instantly. The object gains area and mass, but it doesn't fall to the ground until it becomes to heavy that the updrafts of the storm carrying it can't hold it up. Since NW thunderstorms are relatively weak, we get small hailstones, as opposed to thunderstorms in the plains which can have very strong updrafts, and, as a result, very large hailstones. Snow also begins as a supercooled water droplet, but after it condenses on an object, it grows into a crystal. After this process has started, the crystal can continue to grow at the expense of the surrounding water vapor. How large it grows depends on the humidity and temperature of the air, while how large a hailstone grows depends more on the strength of the updrafts.
It's pretty complicated stuff, and even I don't understand it fully, but I hope that clears up some stuff.
Regards,
Charlie

Thursday, November 5, 2009

Quick Update On the Extended

November 5, 2009
7:39 P.M.

Hello fellow weather enthusiasts. Right now, the front is coming ashore, but we still have a steady rain and will have it until at least midnight, where it will then begin to taper off. I want to talk about the future though after giving such a thorough talk on this current system last night.

After the cold front swings through, we will be under the influence of post-frontal showers. Since the flow will be westerly, the Puget Sound area should be rainshadowed to some extent. I'm not saying we won't get wet, we definitely should get some showers, possibly even some thundershowers, but we won't get as many as other places that are not shadowed. The cool air behind the front will bring the snow levels down to 3,000 feet - pass level - and a winter weather advisory is in effect in the mountains for 5-11 inches of snow. However, Snoqualmie and Stevens passes will be shadowed partially, and they will only get 2-6 inches of snow.

Monday, another strong system will roll in off the Pacific. It will be similar to this one in many ways, but the temperatures associated with it should be much cooler and we should see snow at pass levels throughout the entire event. I'm loving it! It's awesome to get a great base early in the season.

And the good news for snow lovers is that it looks like we should see some snow in the mountains next week. A series of upper level trofts will bring showers to the area as the jet stream directs cool, moisture-laden air off of the northeastern Pacific perpendicularly into the Cascade Mountains, creating clouds and snow. Highs next week should be in the upper 40s and lows in the lower 30s, about normals for this time of year, with showers and sunbreaks in the lowlands and white stuff in the mountains.

I hope you are as excited about the ski season as I am!
Charlie

Wednesday, November 4, 2009

Stress-free Weather/A Note on Atmospheric Thickness

November 4, 2009
8:45 P.M.
I'm sorry I haven't made a forecast more recently... it's just because I've had so much work lately and other stuff in general. My life has been hectic.
With me, weather and stress are inverses of each other. Most people would find their stress relieved by a light drizzle or sunny skies. Nothing takes away my troubles like a fierce windstorm, major flooding, or a blizzard that buries the entire city under 20 inches of snow. Perhaps the rather benign weather as of late has added up to it all. It probably has. However, try using that as an excuse for a poor score on a test. And with the forecast up ahead, it looks like it will all even out. :)



Shown above is a diagram of the 1000-500mb thickness. This model shows the isobars of pressure in the area (note the HUGE 946 mb low in the Gulf of Alaska!) as lines, and the thickness in the atmosphere between the 1000mb and 500mb levels as different colors. The thickness means the physical distance (usually in meters) between the parts of the atmosphere where pressures of 1000 mb (around sea level) and 500 mb (around 18,000 feet). In tropical regions, increased water vapor and temperature make the thickness larger, while the thickness is smaller in polar regions. You can see arctic air/very small thicknesses in the top right hand corner of the model.

Anyway, that low pressure center is very low - about the pressure of a category 4 hurricane - and it will create some inclement weather for us. First and foremost will be waves. 30 foot high swells originating from the intense winds surrounding the low center will hit Washington, starting Thursday and peaking Friday night. Large swells need time to form, an area to form on, and winds to drive them, so this system will be very conductive at producing very large waves.





Next, let's talk about wind. Look at this diagram above. Look at those winds! While they might not be as strong as those found in a hurricane, they cover a huge area, practically the whole northeastern Pacific, with a swath of particularly strong winds SW of the low. These winds will not hit us in their full force but we will see some wind tomorrow, with gusts topping out at around 50 on the coast and north interior and 40 in the Puget Sound basin. Nothing too serious, but definitely noticeable. The lake should be nice and choppy.


In addition, we should get a lot of rain. Right now it is looking like 3 to possible 5 inches in spots in the mountains and an inch or so in the lowlands. There shouldn't be any major flooding, but most rivers should rise significantly, and the Nooksack and Skokomish Rivers have Flood Watches posted for possible flooding.
Looks like tomorrow will be a stress-free day. :)
Have a good one,
Charlie