Cold air has blanketed the region, with low temperatures now ranging from the mid-20s in the western lowlands to lows and single digits in the Columbia Basin (see below). Temperatures drop below 0 degrees Fahrenheit in several valleys east of the Cascade Peak.
The whole area is cold enough to have snow right now, without any moisture.
All the moisture is going into California right now. Good…they need it!
Friday and Saturday will generally be dry in the Northwest, with lots of sunshine.
But on Saturday night, a source of moisture will approach: an obscured front in the Pacific (see forecast map for 7pm Saturday, black lines are sea level pressure, front view) shown as a red line, near-surface temperature in tints).
The front will bring humidity and warming, but the latest modeling simulations show that cold air will build up enough in the heart of Puget Sound to produce a few inches of wet snow Sunday morning (see simulation). UW figures forecast cumulative snowfall through 4 p.m. Sunday).
Lots of snow in the mountains.
With low temperatures, less snow is expected near Puget Sound.
The Central Europe model will have less snow near Sound… about an inch.
Portland forecast bust
The weather forecast is so good, but sometimes the results are disappointing.
And forecasting skills are rarely more of a problem for Northwest snow. Not only are temperatures typically low for snow, but small errors in precipitation intensity can have a BIG impact on snow forecasts.
Remember that 1/10th of an inch of rain in the form of water will produce about ONE inch of snow. An almost ten to one ratio. So small errors are amplified.
Here’s the total snowfall from yesterday in the Portland area. About 8-10 inches around the city.
In fact, Portland’s airport received 10.8 inches, resulting in the second-most snowy day in the station’s history.
How much was predicted? The National Weather Service’s official forecast for Tuesday night is less than an inch! (see below)
A major problem is that models have underestimated circulating moisture around a low-lying region moving down the coast, with a larger range of precipitation around Portland (see satellite images at around 3pm yesterday). ). Forecast is difficult.
