The front is through, the convergence zone has weakened, and a nice day beckons (gardening day for me!). Take a look at the latest high-resolution visible satellite image (attached). Mostly cloud free and sunny over central an southern Puget Sound, with a very weak residual convergence zone feature near Everett. Offshore you will see some scattered...
Wimpy Front, Great Convergence Zone
| comments
The front today had very little precipitation and attenuated cloud, but the convergence today was well-defined with a beautiful precipitation band...take a look at the recent radar image...Way too warm for snow in the lowlands with it... Tomorrow looks generally dry over the lowlands...with some light snow showers in the mountai...
Dense Fog
| comments
There is dense fog around the Sound right now....that is generally a very good sign for day ahead. To get dense fog at low levels, one generally needs intense surface cooling...which generally requires clear or nearly clear skies aloft. You also need little mixing (otherwise you would have a thicker fog layer, which tends to be less thick at any...
Coldest Temps
| comments
The answer to my question in the last blog: the coldest temperatures are generally in the hour AFTER sunrise--so this time of the year around 8 AM. Temperature is controlled mainly by two factors: solar radiation during the day that warms, and infrared radiation emitted by the surface that cools (day and night). When the sun sets there is only infrared...
Dirty Ridge
| comments
A term often used in meteorological circles is "dirty ridge." No, this is not some kind of meteorological pornography. Rather its when there is a "ridge" or area of high pressure that is not strong enough to keep us dry and cloud free. Weather disturbances with sufficient amplitude can inject clouds and rain into the northern portions of the ridge...that...
Coastal Weather Radar
| comments
It is time for all those interested to push for a coastal weather radar in our region.As I have discussed in this blog and in a web page on the topic, http://www.atmos.washington.edu/~cliff/coastalradar.html , the Pacific Northwest has the worst radar coverage of any coastal location in the continental U.S. (see graphic, red indicates no coverage)....
Snow is here
| comments
The snow is here--nearly on schedule (light precipitation almost always starts an hour or two before the models indicate). Look at the radar...light precipitation.pretty much all snow is extensive south of Seattle...but the forecast rain shadow over Seattle and to its north is evident. Temperature aloft are cold enough for snow (as seen in the Seattle...
Rainshadow and snow/rain
| comments
I will update in more depth later...but another Pacific disturbance is approaching (see figure) and we will get precipitation...the question is the how much and whether it will be rain or snow. Because the disturbance is moving towards us from the northwest, there will be a strong westerly component as is approaches and moves over us. Westerly flow...
Humility
| comments
Well, one thing a forecaster learns quckly is humility. There is a weak upper level disturbances that is causing this light precipitation. The heaviest precipitation is on the eastern side of the Sound. Take a look at the radar animation to see the details ( http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?atx_n0r+/2h/ ). The models did not handle this light precipitation well...in most of the region there is no accumulation...but some of you are getting up to around an inch (Woodinville and Snohomish seem to be ground zero for the worst). It WILL end later this afternoon and early evening....guaranteed....
Sunday Morning Update
| comments
The air above us is now cold enough for snow...and there are a few light flurries going on now as the final bands of showers from the passing weather disturbance move through (see figure). Last night some locations received 1/4 to 1/2 inch (a few slightly more)..particularly at higher locations in the North Sound. And as I mentioned last night, the...
Modest Model Failure
| comments
The numerical models from this morning and earlier underplayed the precipitation over the region. The latest runs appear to have caught up with reality with light precipitation this evening. As a result we are seeing a wintry mix of rain, rain/snow mix, and some light snow over the lowlands, particularly north of Seattle. There is a dusting at some...
Snow Update
| comments
The latest models suggest that tonight and tomorrow morning there will be light snow in the Cascades (a few inches at most), and perhaps a dusting SE of the Olympics...and maybe a few flurries over the Puget Sound lowlands....check out the 24-h snow forecast ending 4 PM tomorr...
The Fraser Gap Wind
| comments
One of the more interesting local weather features of our region is the gap flow through the Fraser River valley...and this phenomenon will be quite evident this weekend. In fact, it has already started. Take a look at the topographic map I have attached. The most substantial weakness in the Cascades north of the Columbia Gorge is the Fraser...
Evening Update
| comments
The new round of forecast models retains the same story...some cooler air moving in on Saturday and Sunday, but no snow over the western Washington lowlands. Perhaps a few light snow shower near Portland. In fact, it looks like the skies over Puget Sound will clear on Sunday and you will see some sun. A big issue is that the mountains have not received any new snow in while. Icy and no powder. The only silver lining is that this snowpack is solid and stable. They don't call it Cascade concrete for nothing...so very small avalanche thre...
Cold, but no snow in Seattle
| comments
I have been studying the latest computer forecasts and it is clear that this weekend will bring major changes....but no snow in Seattle.Starting with today, low clouds and the inversion are still in place over Puget Sound and eastern Washington (see satellite picture and the latest profiler temperatures in Seattle). The inversion is a weaker than...
Transition to colder air over the weekend
| comments
Several of you have commented on the potential for a transition to much colder air over the weekend. I have held off talking about it until we were close enough, but now it seems clear we will move to much colder air overhead later on Saturday. By Monday will be deep in moderated arctic air (see forecast output for 4 AM Monday). Blue indicates air...
Black Ice
| comments
What is the the weather condition that kills and injures more Washington State residents than any other? Floods...no. Windstorms..no. Tornadoes or Thunderstorms. No way. I am pretty sure it is roadway icing...and that threat is very real this week. Roadway icing is often called "black ice"--but it really isn't really black...it can look dark...
Videos at top of Tiger Mt Yesteday and Fog Today
| comments
If was quite windy at the top of Tiger Mountain yesterday, with easterly winds probably gusting to 25-30 knots. Check out the video I made up there. Also, I have a pic of my thermometer reading at the top...just in case no one believed me!We have a cam in the department, and it is interesting to view the layer of fog today...which was just below...
Ascent of Tiger Mountain and Warm Temps
| comments
Today was a very different day than those of earlier this week in a number of ways. First, the fog and low clouds were considerably reduced west of the Cascades, particularly in the afternoon (see the sat picture at 2 PM). Low clouds did remain east of the Cascades and extended into the pass.The pressure difference across the Cascades increased to...
Fog in the pass
| comments
Several of you have asked about the fog in the pass...they thought the mountains should be clear due to their higher elevations...and in fact they have been clear for several days. The cams in Snoqualmie Pass (see attached) do show fog. In fact, the fog has been freezing on trees and other objects. Yet on top of tiger mountain and at Paradise...
Great image
| comments
This is an ultra-high resolution image from NASA Aqua satellite....much better quality than the NWS geostationary satellites I have shown you in the past...but only available twice a day (click on the pic to see it better). You can see so clearly the low clouds over Puget Sound and eastern Washington. Look carefully and you can see fingers of low...
Air Quality Questionnaire
| comments
There is a little mystery going on for the air quality folks...why air pollution hasn't increased more with such a strong inversion. Have people reduced their burning of wood without a burn ban? To help answer this question, they have put together a brief web questionnaire, and if you have a few minutes, please give it a try:http://www.atmos.washington.edu/weatherforecasting/airquality/index.phpand...
Even Lower
| comments
Here is a wonderful picture from Stephen Van Dyck that was taken at Poo Poo Point (1820 ft) on Tiger Mt. yesterday afternoon a 4 PM. The same view will be available today. Hiking through a sharp inversion is a real treat. If you don't like hiking, drive up to the top of Cougar Mt. Park and bask in the sun.The inversion is lower and stronger this...
