Thursday, April 1, 2010

Storm on the Way

Thursday, April 1, 2010
4:05 P.M.

Hey everybody. The storm is on it's way. We have a lot to look at. The four frames above show the development of the low pressure system according to the NAM model in three hour frames from 2 A.M. Friday to 11 A.M. Friday. First, though, let's look at a current water vapor satellite image. This image shows the temperature of the tops of the atmosphere, and the colder the water vapor, the higher the cloud tops, and generally, the stronger the storm and heavier the precipitation.
Can you see the bent-back occlusion starting to develop? Also, there is the dry slot which is becoming more well formed by the hour. It is that dark spot to the west of the cloud shield associated with the storm. These are the trademark signs of cyclogenesis - the intense development of a mid-latitude cyclone.
The models that came in earlier this morning were similar to those that came in last night except that they had further diverged. The GFS was even weaker and further south and the NAM was even stronger and was further north. Based on the satellite image I see now, I'm going to go with the NAM. I have to be cautious and exercise restraint but I still believe that the NAM is the superior model in this situation. I predict the actual storm to be a combination of the two models - meaning it will have a central pressure of 975-980 millibars and will come ashore southern Vancouver Island.

The winds will be strongest on the coast. Places on the exposed beaches could have winds of 80 mph and coastal headlands could have isolated gusts to 100. That's extremely powerful. The same is true for the mountains, as mountain ridgetops could have some very strong winds as well. A high wind warning is in effect for the coast as well as the northern and southwestern interiors for gusts up to 60.

We are still not sure if Seattle will get winds reaching high wind criteria because of the uncertainty of the track of the low. Based on the cyclogenesis I see occuring, I'm predicting a marginal high wind event, with top gusts in our area ranging from 50 to perhaps 60 miles per hour. Let's hope that we witness this. Or, well, at least I hope we do. :)
This shows the predicted 24 hour snowfall charts for Friday ending at 5 A.M. (less than 24 hours - from the initiation of the model on, which was probably around 7 A.M. - I could be wrong). The second frame shows the snow expected from Friday 5 A.M. to Saturday 5 A.M. A winter storm warning is in effect for the Cascades for 1-3 feet of snow from this storm with locally higher amounts. Travel through the passes will be dangerous with heavy snow and blizzard conditions at times.
The lowlands will see an inch or so of rain with this event. Places like Sequim and slightly west of it will be heavily rainshadowed by a southwesterly flow.
I'm gonna be flying a huge kite and shooting some video on a very well-exposed beach on Whidbey Island. Have fun and enjoy this storm!

Weak storm coming

Thursday, April 1, 2010
12:05 A.M.
So there's a weak storm coming in later today. Not much to talk about.

The strongest storm of the year looks to come in later today and especially on Friday. So strong in fact, that I've cancelled my prospective visit to UBC to check it out. Models are in disagreement right now among the exact details, but they are in general agreement that we will get a strong storm. The GFS model, which is usually a little more accurate, is the weaker of the two. This frame of it shows the expected winds at 5 A.M. Friday and shows the strong 988 low pressure center off the coast. Peak winds in our area will probably occur around noon after the low deepens to 984 millibars at Tatoosh Island and heads into southern British Columbia. That scenario would give high winds to the coast and north interior wind wind advisory level winds (gusts up to 58 in isolated spots) in the Puget Sound area. What really caught my eye, however, is the NAM model.

This model shows a developing 984 mb low off of our coast, which will then mature to 980 millibars as it heads into Barkley Sound off southern Vancouver Island. This, I believe, could bring high winds to the lowlands, and it is something we will have to watch for. If this scenario came true, I predict we could see some damaging winds in the lowlands and some power outages. Get ready!

Another aspect of this storm will be the precipitation associated with it. Precipitation totals could be around an inch in the lowlands from this storm and nearly 4 inches in some places in the mountains. Much of that will fall as snow, meaning some places could see as much as 40 inches from this one storm! This above image, taken from the NAM model, not only shows the precipitation field associated with the storm but shows the bent-back occlusion, the trademark of a strong storm.

And, of course, there is the snow. This chart shows the 24 hour snowfall from 5 A.M. Friday to 5 A.M. Saturday. They are monstrous! Widespread amounts of 1 to 2 feet are found in the Cascades. Add that to the additional foot the day preceding and day following and you are talking about 3-4 feet of snow from this one storm in the mountains. These is very unusual for April. I hope it keeps up though! And models do show a weaker, cool storm settling in early next week for some more snow in the mountains. :)
Enjoy what may be the strongest storm for some while!