Sunday, December 23, 2012

White Christmas?

Sunday, December 23, 2012
10:46 P.M.

First off, let me apologize for not being more punctual when it comes to posting on this blog. I had three pretty rough finals in two days, and the evening after my last final, I had a seizure (which may have been related to the stress... who knows), so I've been trying to collect my thoughts and just relax my first week of break.

I feel no shame in telling people that I have epilepsy on this blog, and I honestly did the best I could on my finals. My medications to control epilepsy make abstract thinking and high-level cognition difficult, something which is kind of necessary for the high level science classes I am taking. So it's taken me a little while to try and enjoy my break since the quarter ended, but I'm feeling a bit better now. Some successful businessman guy named Bo Bennett said that "frustration, although quite painful at times, is a very positive and essential part of success." That will probably make more sense when I'm less frustrated.

It's ok though. Because in the end...


I have some very positive news for you all. Parts of the region could see a White Christmas. Of course, forecasting snow here is pretty intimidating, particularly when I'm forecasting for kids who are in school. Thankfully, there's no school on Christmas anyway, so the stakes are a little less high with this forecast. In addition, this is only forecast to be a minor snow event.

The National Weather Service released a Special Weather Statement for Western Washington highlighting the possibility of snow in places for Christmas Day. I've reprinted it below for your viewing convenience.


A PACIFIC FRONTAL SYSTEM IS EXPECTED TO IMPACT WESTERN WASHINGTON
ON CHRISTMAS DAY. THIS SYSTEM HAS THE POTENTIAL TO PRODUCE SNOW OR
A RAIN AND SNOW MIX ON THE LOWLANDS AS WELL AS MORE SNOW IN THE
MOUNTAINS ON CHRISTMAS DAY.

THE PRECIPITATION WILL PROBABLY START OFF AS A RAIN AND SNOW MIX
ON THE COAST DURING THE EARLY MORNING HOURS OF CHRISTMAS AND SNOW
ON THE INTERIOR LOWLANDS CHRISTMAS DAY. SOME INTERIOR LOCATIONS
MAY SEE A RAIN AND SNOW MIX TO START AS WELL.

AS WARMER AIR MOVES INLAND DURING THE DAY...EXPECT THE SNOW TO CHANGE
OVER TO RAIN. SNOW LEVELS MAY BEGIN AROUND 500 FEET AND RISE TO
1000 FEET OR MORE LATER IN THE DAY. ONE OR TWO INCHES OF SNOW
ACCUMULATION IS POSSIBLE IN HIGHER ELEVATIONS PRIOR TO THE
PRECIPITATION TURNING TO RAIN.


A white Christmas is defined as having one inch or more of snow on the ground. December 25, 2008 had around half a foot of slush at my house, so it technically counts as a White Christmas, but it was a pretty sloppy one. I still remember December 26, 1996, when we had a White Day-After-Christmas. It was incredible. The snow was almost as tall as me. As I grew older, I got the whole memory mixed up, and thought that it had actually snowed on Christmas Day. I remember not being surprised waking up to all the snow, because in my mind, it was supposed to snow on Christmas. That's just the way things were. "Tide goes in, tide goes out. You can't explain that." (Bill O'Reilly). And you can't explain snow falling on Christmas Day. It just happens.

Of course, I've grown to recognize over the years that Christmas Day is usually rainy, not snowy. There is less than a 10% chance of having a White Christmas on any given year.

So what's my outlook for snow chances in the lowlands? Some places with elevation and away from water may see some snow to start, but it will not accumulate and it will change to rain pretty quickly. I live down by Lake Washington, so I'll see all rain. The lowland spot with the best chance of getting some snow is Hood Canal. As has happened in recent weeks, cold air has a harder time being flushed out by storm systems in the Hood Canal area, and snow often occurs there even when there is a chilly rain throughout the rest of Western Washington. Let's take a look at the UW WRF-GFS model to get a better idea of what we are dealing with.

Valid 04:00 pm PST Tue, 25 Dec 2012 - 48hr Fcst - UW 00z 4km WRF-GFS Western Washington 24-hour snowfall

As you can see, the only accumulating snow that will fall on the lowlands on Christmas is in the Hood Canal region. Places like Hoodsport, Potlatch, and Skykomish could see anywhere from 3-6 inches of snow, with lower amounts near the water and much higher amounts as you go closer to the Olympics. The snow doesn't quite make it to Olympia.

The Cascades will definitely get some snow. I, for one, am dying to get back on the slopes, and I hope to do so after Christmas. I haven't skied in two years though, so there is a decent chance I will fall flat on my face more than a couple times. I'll just get back up and show that mountain who's boss. That's how we grow.

Merry Christmas!
Charlie

Sunday, December 16, 2012

An Update!

Sunday, December 16, 2012
2:40 P.M.

Hi everybody! It's great to be back! I survived finals, although I sustained some serious injuries during the battle. Oh well, I'll recover from them soon enough.

We've got a lot to talk about. First off, we have a fairly large storm swinging through our area tonight. Take a look at all those pretty warnings over the region. This is what I live for.


Not a country spared. Wonderful.

The main things I want you guys to look at are the high wind warnings over much of Western Washington and the blizzard warnings over the Cascades and Olympics. High wind is relatively common around the coast, but it is much rarer inland. The one place that doesn't have high wind warnings in effect is the Tacoma - Mt. Vernon region, as the strongest pressure gradients will reside south and west of there. It should still be noticeably blustery though, and a wind advisory is in effect in that region. Blizzard warnings represent the penultimate National Weather Service severe winter weather warning, and denote sustained 35 mph winds with heavy snow for at least three hours at a time. I was taking a look at some of the pass cams, and they don't look too bad yet.

But this will change. 1-3 feet of snow is possible through Monday night, and gusts to 60 in the passes and up to 90 on exposed ridges will pummel the Cascades and Olympics. This is not the time to be out backcountry hiking or skiing, as conditions could become life-threatening. It's also probably not the best time to try and make it across the passes either, although if you got a whole bunch of people up there, you could probably have a pretty large snowball fight.

Let's take a look at the current satellite.

02:30 pm PST Sun 16 Dec 2012

As you can see, there is clearly a strong storm racing into our area. It's fairly mature as far as its development goes, and we are probably already in the occluded part of the cyclone. There is a well-defined dry slot and an extended bent-back occlusion west of the center of low pressure. It's not the prettiest cyclone I've ever seen, but looks can be deceiving. This will be a strong storm.

The coast will see the greatest effects, but this should hardly come as a surprise; the coast always sees the greatest effects. There is a storm warning over all the offshore waters from Cape Flattery to the Californian border for sustained winds of 40 to 50 knots and associated waves of 20-25 feet. Vessels should stay in port. I can't even imagine what the bars will look like. It would be interesting to see the Grays Harbor and Columbia River Bars at ebb tide with waves this large. It would also be something that would be extremely dangerous to all but the largest vessels.

The storm passes through Monday morning, but that definitely won't be the end of its effects over the region. Particularly, I've got my eye on Monday night, where a possible convergence zone could bring some snow to the hills in the favored southern Snohomish/northern King county regions. This won't be a major event, and the snow won't stick around for long, but it could be the first significant snowfall for parts of the region this year.

After that, we look to continue in our unsettled ways, but the models are all over the place with regards to the details. One thing is for sure... the mountains will continue to see lots of snow, and that's all I could really ask for Christmas.

Enjoy the gloomy weather!
Charlie

Monday, December 3, 2012

Watching the Satellite

Monday, December 3, 2012
10:36 A.M.


10:00 am PST Mon 03 Dec 2012 - UW West Coast 4km water vapor satellite

Good morning everybody, I hope you are all having a nice first week of December. It was pretty rainy last night, but we'll be heading into some calmer weather soon.

However, we've got a storm to go through first.

Sometimes, there is a large discrepancy between what the models initialize the current state of the atmosphere to be and what the atmosphere actually looks like on satellite. One example of this was the snow event back in January 2012 (which was probably my finest moment as a forecaster because I totally went against the models and ended up being correct). But looking at this satellite image compared to the initialization, you can see some pretty big differences. Let's first look at what the models say what the atmosphere should be like right now. This is 6 hours after the initialization because the UW doesn't have this model map for the initialization.

Valid 10:00 am PST Mon, 03 Dec 2012 - 6hr Fcst - UW 12z WRF-GFS 36km outgoing longwave radiation (similar to infrared satellite)

Take a look at that swath of clouds offshore. That's the low pressure wave that's expected to develop and slam into our area Tuesday morning. Now, let's take a look at the actual infrared satellite.

10:00 am PST Mon 03 Dec 2012 - UW West Coast 4km NWS infrared satellite

As you can see, the maps generally look the same, but there are some important differences. In the actual infrared photo, there is more of a "hook" at the upper left portion of the storm. This is called a bent-back occlusion and it is a classic feature of strong cyclones. This occlusion is not very pronounced in the infrared satellite.

For an even better comparison of images, take a look at the water vapor satellite picture.

10:00 am PST Mon 03 Dec 2012 - UW West Coast 4km NWS water vapor satellite

There is a very pronounced "dry slot" here, which is another indication of a strong cyclone. The low pressure center is typically located within the dry slot. 

Do I think we are going to see a major windstorm out of this? No. The cyclone is not developing very quickly and the jet stream supporting it is not particularly strong. However, I do think this is something the NWS service should keep an eye on. In their 9:15 forecast discussion, they mentioned issuing a wind advisory for the coast and north interior later today. They may have to upgrade that to a high wind warning, at least for the coast, and they may also have to issue a wind advisory for the Puget Sound lowlands if this storm comes in stronger than expected. It won't be a megastorm by any means, but it just goes to show that models aren't perfect representations of the atmosphere at a given time, and these satellite images show that.

Off to calculus, send your prayers my way. :)
Charlie