Revised LAWES Scale

Friday, January 13, 2012
3:11 P.M.

Don't judge me... this is the most relevant picture I could find.

I first invented my LAWES scale in November of 2010. It has been hailed as one of the most innovative weather scales of the 21st century by the followers of this blog ever since, but I have noticed a couple of its shortcomings over time, and it is time I update my LAWES scale to address these.

First, I made my LAWES level 3 more specific, replacing "a few days" with "5 days." Second, I added a new level that was between the old levels of 3 and 4 (now 3 and 5). The new level is now LAWES Level 4, and adds specificity to the scale by saying that the models are in a reasonable consensus about getting snow in 1-3 days. The percentages for LAWES Level 5 (previously Level 4) have been updated as well; there is now an 80-99% chance of snow with this scenario.

It's not over yet! I also added a .0 to the second part of the LAWES scale to describe situations where it doesn't make sense to forecast snow totals because the potential event is too far out. This was desperately needed, as I felt I couldn't properly use my scale when a snow event seemed to be lurking but the exact details were unclear. I also changed the range of snow predicted for each level more accurately reflect uncertainty in the art of forecasting, particularly the art of forecasting snow in Western Washington.

Remember, the first part of the scale explains the probability of snow, and the second part explains the amount of snow forecast. For example, a level 5.5 would mean that there is a 80-99% chance of snow and the snowfall totals would generally range from 6 inches to a foot. That is a pretty high LAWES level. Sometime in the future, I'd like to type that as an actual prediction and not as an example!

The scale predictions are centered around the Seattle metropolitan area, but they generally apply to all of Western Washington. When a situation nears, I will start to outline snowfall predictions for certain areas, as it is not uncommon for some places to get a foot of snow while places 30 miles away get absolutely nothing, especially with Puget Sound Convergence Zone events.

I'll print both scales below, so you can see the changes. The revised scale is on the bottom.

Old Scale:


LAWES level 0: You are on a planet that has the ingredients necessary for snow
LAWES level 1: Models are showing a chance of snow beyond a week out, 0-20% chance of snow
LAWES level 2: Models are showing a chance of snow within a week, 20-40% chance of snow
LAWES level 3: Models are all showing a scenario that would easily produce snow within a couple days, 40-60% chance of snow
LAWES level 4: Places around the area are already getting snow AND snow is forecasted for Seattle, 60-99 % chance of snow
LAWES level 5: Snow is occurring, 100% chance of snow (derp)

Ending in:
.1 - 0-2 inches of snow
.2 - 2-4 inches of snow
.3 - 4-6 inches of snow
.4 - 6-8 inches of snow
.5 - over 8 inches of snow
.6 - board the next plane to Panama


New Scale:

LAWES Level 0: You are on a planet that has the ingredients necessary for snow
LAWES Level 1: Models are hinting a chance of snow beyond a week out, 0-20% chance of snow
LAWES Level 2: Models are showing a chance of snow within a week, 20-40% chance of snow
LAWES Level 3: Models are showing a scenario that would produce snow within 5 days, 40-60% chance of snow
LAWES Level 4: Models are in consensus about a snow event 1-3 days out, 60-80% chance of snow
LAWES Level 5: Places around the area are already getting snow AND snow is forecasted for Seattle, 80-99% chance of snow
LAWES Level 6: Snow is occurring, 100% chance of snow (derp)

Ending in:
.0 - the event is too far out to pin down snow totals
.1 - up to 2 inches of snow
.2 - up to 4 inches of snow
.3 - 2-6 inches of snow
.4 - 4-8 inches of snow
.5 - 6-12 inches of snow
.6 - board the next plane to Panama

Tell me what you think of the new scale! And, if you have any suggestions for improving it, let me know!

Now, let's move on to our forecast.

We have several different snow events on the horizon. Our first shot at snow begins Saturday and lasts into Wednesday. I'd give us a LAWES rating of 4.1. Places will probably get snow, but it won't be that much and it will be hard to pinpoint which places will see the highest amounts. A Puget Sound Convergence Zone will probably form, meaning that places between north Seattle and Everett could see higher amounts... possibly much higher if it lasts for a long time. It is very hard to forecast the locations of these convergence zones though, so anywhere from Burien to Mt. Vernon should be on the lookout for one of these zones.

I personally think that most lowlands will get more snow than is advertised here. Due to the spotty nature of this incoming storm, some places will see no snow, but I believe Seattle could receive up to 2 inches with this storm. The models tonight will give us more details.

The real interesting stuff comes in next week. Some models have hinted at over a foot of snow for Seattle!!!

Ok, I probably shouldn't have said that, because now people are gonna run around and say that I forecast a foot for Seattle and then get mad at me when we get rained on. I do believe that we could get some significant snow next week though.

For now, I'm giving our snow chances next week a LAWES 5.3. I'll have more details after tonight's model runs, and I'll post again either tonight or tomorrow.

Thanks for reading!!!
Charlie

LAWES 2.1

Wednesday, January 11, 2012
11:14 A.M.

I don't have too much time here, but I thought I'd give you an update on the forecast for this weekend and beyond. It seems as though most forecasters are much more conservative as far as snow goes.

In fact, here's what the KOMO forecast had to say this morning.

A few thoughts about this snow chance:  It is marginal at best.  It won't be that cold and it isn't forecast to be that wet.  Any trend drier or milder will eliminate this snow chance entirely.  That said, if we get just a little more moisture, snow may in fact accumulate (I consider an 'accumulation' more than 1" on the ground) in the lowlands.

I disagree with this statement. I think we have more than a marginal chance of snow. Which leads me to my own snow scale rating!

For a refresher, it is printed below.

So, lets go through this scale.
LAWES level 0: You are on a planet that has the ingredients necessary for snow
LAWES level 1: Models are showing a chance of snow beyond a week out, 0-20% chance of snow
LAWES level 2: Models are showing a chance of snow within a week, 20-40% chance of snow
LAWES level 3: Models are all showing a scenario that would easily produce snow within a couple days, 40-60% chance of snow
LAWES level 4: Places around the area are already getting snow AND snow is forecasted for Seattle, 60-99 % chance of snow
LAWES level 5: Snow is occurring, 100% chance of snow (derp)

Now, notice how there are no measurements for how strong a Seattle snowstorm could be. But have no fear! That's what suffixes are for. 
Ending in:
.1 - 0-2 inches of snow
.2 - 2-4 inches of snow
.3 - 4-6 inches of snow
.4 - 6-8 inches of snow
.5 - over 8 inches of snow
.6 - board the next plane to Panama

I'm gonna go with a LAWES (Likelyhood of an Arctic Weather Event with Snow) 2.1 at this point. I'm pretty confident that some places in Western Washington will get snow, but I'm not quite sure that Seattle will get snow, so it would be around a 40% chance of snow in Seattle at this point. I'm not sure how much snow there will be yet (models are all over the place, so I'm going with a 0-2 inch estimate in Seattle for right now. Other places could get more. Still, I don't think we will be boarding the next plane to Panama anytime soon.

This probably won't be an event like 2008, but it has the potential to be major. It's really hard to tell this far out though. Heck, some forecasters around here can't predict snow 30 minutes in advance.

Valid 04:00 am PST Mon, 16 Jan 2012 - 120hr Fcst - UW 12z 12km WRF-GFS 24 hour snowfall

You can see some light accumulations in the Western Washington lowlands, with heavier amounts in the mountains. Remember, the GFS is showing the least snow of all the models, but it still gives Seattle a bit of snow. It's not much, but it's a good sign. 

The 180 hour frame is pretty exciting as well! Of course, you can't take this seriously, but it's fun to look at! Lots of snow to our south.

Valid 04:00 pm PST Wed, 18 Jan 2012 - 180hr Fcst - UW 12z 12km WRF-GFS 24 hour snowfall

Now, one more quick picture from the European model. 

Valid 04:00 am PST Sun, 15 Jan 2012 - 96hr Fcst - ECMWF 500bm thickness, SLP

You can see a big trough over the Pacific Northwest, giving us cold temperatures and some precipitation, especially in Oregon.

Gotta go! College calls.

Charlie

Sea-Level Snow Looking Pretty Likely

Tuesday, January 10, 201212:48 P.M.

Photo Credit: Alistair Grant

I'm actually taking a class that discusses the current weather over the world once every week, so I thought I'd go ahead and post my notes on my blog! Of course, it will be more of a summary/story of my notes, because my notes are pretty boring. Three major events occurred over the past week.

First of all, there was a gigantic storm in Scotland over the past week. The picture above is one of the most incredible pictures I have ever seen. A wind turbine spun so fast from the howling winds that it caught fire. I've never seen anything like that. Winds gusted up to 165 miles per hour during this storm, and while that reading was most likely taken at an exposed coastal headland, it is nonetheless extraordinary.

Second, there was a HUGE heat wave over the upper Midwest! A large ridge of high pressure centerred itself over the Midwest during the middle of last week, pushing the arctic air that normally invades the region far north and allowing warmer, southerly winds to push into the area. Certain places got into the 70s!

Take a look at the model below... it shows the forecast as it was initialized on 00z Thursday, January 5th. A massive ridge

Valid 04:00 pm PST Wed, 04 Jan 2012 - GFS 500mb heights, SLP

Now, on to snow in Alaska!

The huge ridge that has dominated the Eastern Pacific for most of this winter has left us with fairly boring weather. However, there are still storms, and these storms have been directed northward into Alaska. One particular town named Cordova has seen over 10 feet of snow, with some people being snowed into their homes, unable to open their doors. The U.S. National Guard has been called to assist the town in recovering from the snowstorms. Mother Nature will help out too, and although there will be snow, it won't necessarily be directed into Alaska.

Remember how I blogged yesterday about inconsistencies in the models? While the models aren't in complete agreement yet, the cold models (Canadian and ECMWF) have become colder, and the warm,  boring model (GFS) has become pretty chilly. As an added bonus, the Canadian is generally a better model than the GFS, and the ECMWF puts the GFS to shame.

Take a look at the current ECMWF model from 12z this morning!

Valid 04:00 am PST Sun, 15 Jan 2012 - GFS 500mb heights, SLP

See the huge ridge in the Eastern Pacific and a huge trough over us? That is a classic scenario for frigid air to invade our region. If this scenario came true, we'd see some very, very cold air with snow to boot.

King5 is already forecasting snow for the weekend. http://www.king5.com/news/local/Snow-at-sea-level-expected-this-weekend-137030773.html. Normally, I wouldn't jump on a snow scenario this quickly, but it is looking like we will get some snow over the weekend into early next week at this point.

Charlie



Inconsistencies in the Models

Monday, January 9, 2011
11:06 A.M.

As I sit in the Ocean Sciences building waiting for my "Climatic Extremes" class, I can't help but wish for more exciting weather around here. Thankfully, some of the models are giving me some hope that we could see change, but other models give us weather that is even more boring than it has been over the past two weeks (if that is possible).

Here is what the National Weather Service forecasting office in Seattle had to say about the extended forecast this morning.

LONG TERM...PREVIOUS DISCUSSION...EXTENDED MODELS IN GOOD AGREEMENT 
THROUGH FRIDAY WITH AN UPPER LEVEL RIDGE OVER WESTERN WASHINGTON AND 
LOW LEVEL OFFSHORE FLOW. MODELS ARE A LITTLE STRONGER WITH THE LOW 
LEVEL OFFSHORE FLOW WHICH LESSENS THE THREAT OF STAGNATION. MODELS 
BECOME VERY INCONSISTENT OVER THE WEEKEND WITH THE GFS KEEPING THE 
RIDGE IN PLACE WHILE THE ECMWF BRINGS A COLD TROUGH INTO THE AREA. 
BY 00Z MON THE GFS HAS 500 MB HEIGHTS OF 567 DM OVER SEATTLE WHILE 
THE ECMWF HAS A 534 DM HEIGHT OVER SEATTLE WITH PLENTY OF 
PRECIPITATION. MODEL ENSEMBLES ARE NOT MUCH HELP OVER THE WEEKEND 
WITH WIDE SPREADS IN THE SOLUTIONS. IN GENERAL THE ECMWF HAS BEEN 
VERIFYING BETTER AND THE FORECAST IS TRENDED IN THAT 
DIRECTION...JUST NOT AS COLD AS THE CURRENT MODEL RUN WOULD SUGGEST. 
CONFIDENCE IN THE FORECAST OVER THE WEEKEND REMAINS LOW. FELTON 

Here, Mr. Felton is saying that the models are all over the place in terms temperature and precipitation in the extended. The GFS model (from the NWS) builds a ridge over us for the weekend (boring) while the ECMWF (European) model gives us colder air with rain in the lowlands but low snow levels in the mountains.

Since the European model is verifying better and is painting a more exciting picture for the extended, I'll show you some pictures of the current model run.

Valid 04:00 am PST Mon, 9 Jan 2012 - ECMWF 500mb heights, SLP

Right now, we have a front to our north, bringing up warm air from the south and giving us some clouds. We will get rainier later today, but after that, we'll be pretty dry again.

A bigger ridge builds up by Wednesday, with the jet stream going all the way up into Alaska.

Valid 04:00 am PST Wed, 11 Jan 2012 - ECMWF 500mb heights, SLP

4 minutes till class...

Take a look at the 168 hour frame! A huge ridge over the Eastern Pacific, but a huge trough over the Pacific Northwest. This is a classic setup for arctic air to invade our region.

Valid 04:00 am PST Mon, 18 Jan 2012 - ECMWF 500mb heights, SLP

Of course, the GFS completely disagrees. But at least there's hope. :)

Charlie

My Weather Station!

Thursday, January 5, 2011
9:38 A.M.

 

I hate to say it, but the weather so far this year has been incredibly boring. Sure, we've had a couple rain events here and there, and we did have a windstorm on Christmas Day, but for the most part, even thinking about the weather around here has made me sleepy. That's partly why I haven't updated my blog lately (although to be fair, I was also catching up on some family time when I was home for the holidays).

One thing that actually is pretty cool, though, is a weather station I set up on a beach-house my family owns on South Whidbey Island. You can see the statistics in real time at this link.

This link shows you the current temperature, the high and low temperatures of the day and the times at which they occurred, the current humidity outside, the total rain for the day and year, and the current barometric pressure.  For some reason, the anemometer is not currently reporting, so I'll have to fix that the next time I head up there, but this spot has great southern exposure, so we could see some pretty high readings next time a windstorm strikes our area!

If you are looking for some interesting reading, check out Scott Sistek's 2011 weather year in review here. 

I gotta go to class! By the way, I have a pretty intense schedule this quarter, so my blogging may be less frequent, particularly if the weather continues to be boring. But, when the big storms roll in, I'll leave my homework for some other night.

Thanks for reading!