Wetand News

 This is a question I am often asked?   How far out into the future can we predict the weather? Listen to my podcast and I will provide the surprising, and complex, answer. But first a few hints.... The National Weather Service has a website that shows how weather forecast skill declines over time (see below).  This figure indicates how the forecast skill at roughly 18,000 ft (500-hPa) declines over time for the U.S. global model (NCEP), the Canadian model (CMC), and the gold-standard European Center (ECMWF).   1 indicates a perfect forecast.  When this measure (the anomaly correlation) drops to 0.6 the forecast becomes only marginally useful. Forecasts are very good through 3 days.  Quite good though five days, but then rapidly declines after that.   Some skill continues even two weeks out, but it is very marginal. Another way to see the decline in skill is to look at a series of weather forecast maps for increasing forecast projection. Here is the analysis (truth) for sea level press

 We can still expect to see lowland snow tomorrow, and being closer in time, I have powerful additional forecasting tools to apply. But before I do so, let me note that there was a magnificent auroral display last night, mostly behind the clouds, and during some openings, the sky was aflame. Here is an image from North Kitsap, provided by weather cam maestro Greg Johnson of Skunk Bay Weather.  Stunning. Back to snow.    This is late season for western Washington/Oregon snow and temperatures are marginal.  But with sufficient precipitation intensity, melting and evaporation can drive the snow level down to the surface.   The result:  wet snow. The latest forecasts are converging on around 2 inches near sea level, but as we will see, there will be considerable variability. The feature of interest is a low center (and associated fronts) that is centered off the Oregon/Washington coast right now (see image).  Right now some weak bands of precipitation are over land.  Some light drizzle and

 Special Message:   Could be a major aurora tonight (Sunday) for our region.   Lots of clouds right now, but there should be some clearing in a few hours in western WA. -------------------- The snow forecast went quite well this morning over western Washington, with portions of central Puget Sound picking up the predicted 1-2 inches (see observed snowfall noted this morning by the CoCoRahs cooperative network).   This was a very difficult forecast, with marginal temperatures.   The kind of forecast we could not have done 15-20 years ago. But there is a downside to this increased forecast skill, a negative impact that directly affected me this morning (see below).  I was REALLY looking forward to a pastry and cup of coffee before I went to work at the UW.   No luck. Another snow event for western Washington looms.....and another difficult forecast. Why difficult?  Because major weather prediction models were in disagreement about a crucial weather feature, and we are close to the edge

 We are currently at the end of the normal lowland snow period in the Pacific Northwest, with the sun rapidly strengthening.    But not this year.   The latest forecasts have significant lowland snow over western Washington during the next few days, with many of you experiencing several inches of the white stuff. And we have an extended, colder-than-normal period ahead.   Let me give you the details of the forecast. Today, we have a cold air mass over the region...cold enough to snow anywhere in Washington State.  Temperatures dropped into the teens and twenties in western Washington and single digits in eastern Washington (see low temperatures below).  Several daily low-temperate records fell last night. This evening a moist occluded front will approach, spreading precipitation over the region.   Snow will move into the Puget Sound region after 8 PM. Note that the story in the Seattle Times is very wrong, suggesting snow will come in this afternoon around 4 PM.  It also talks about an

 Frigid air has settled over the region, with the low temperatures today ranging from the mid-20s over the western lowlands to the teens and single digits in the Columbia Basin (see below).   Temperatures dropped to below zero F over some valleys east of the Cascade crest. The whole region is plenty cold enough for snow right now, there just isn't any moisture. All the moisture is going into California right now .   Good...they need it! Friday and Saturday will be generally dry over the Northwest, with plenty of sun. But Saturday night, a moisture source will approach:  a Pacific occluded front (see forecast map for 7 PM Saturday night, black lines are sea-level pressure, the front shown by a red line, the near-surface temperature in color shades). The front will bring moisture and warming, but the latest model simulations suggest that cold air will hold in enough in central Puget Sound to produce a few inches of wet snow on Sunday morning (see UW model forecast accumulated snowfal

 When one thinks of San Francisco weather one generally does not think of snow, but the latest model runs are going for flakes falling around the city. For example, the European Center's model accumulated snowfall forecast through 10 AM Friday has substantial snow on the hills around San Francisco, with snowflakes reaching the Airport.    The U.S. GFS model has even more...snowflakes over the entire city! Forecast temperatures for 4 PM Thursday are 15-25F below normal (see European Center Forecasts below). The media is going crazy with this snow talk for the "City by the Bay", warning of "wintry blasts".   Highly dangerous conditions for the city's large homeless population. How unusual is snow at the airport in San Francisco?  As shown below, measurable snow only occurred there ONCE--in January 1962. Huge snowfall totals are expected during the next week over California during the next five days (see forecast below). Yards of snow. And deep snow will even f

 In a paper I wrote several years ago on western Washington snowstorms, I list several ways snow can fall in the area. All had to find a way to provide precipitation and cold at the same time-- which is very difficult in our neck of the woods. One way to get snow...generally light snow.. is with the passage of an Arctic Front (really a modified Arctic Front, but who is checking?) And we are going to get some snow from such an Arctic Front passage on late Tuesday and on Wednesday morning. In a western Washington Arctic Front passage, cold air from the interior of British Columbia surges southwestward through the Fraser River Valley and jets out just north of Bellingham.  The frigid flow splits around the Olympics with a river of cold air pushing southwards over Puget Sound. The Arctic air collides with warmer/moist air to the south, pushing some of it upwards producing clouds, precipitation, and yes, snow. Later tomorrow, the Arctic air will push southward, as illustrated by the foreca