12/21/2014

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Snow chance threatens morning commute, meteorologists' sanity

Snow chance threatens morning commute, meteorologists' sanity
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SEATTLE -- As we continue to monitor whether lawns will be white or green for the Friday morning commute, one thing is for sure: local meteorologists' hair have a 100 percent chance of turning grayer.

Your local weather forecasters are dealing with a very complex forecast in where data and forecast models suggest it will snow, then rain Thursday night into early Friday morning. The trick we're dealing with is: How long it will snow, how much snow will fall, and whether pitchforks are still on Black Friday sales if it doesn't snow much at all.

Here is what is for sure: A warm front moving in from the northwest will spread precipitation to the coast around midnight and push that into the I-5 corridor from northwest to southeast during the predawn hours.

The computer forecast models are still indicating that the air is just cold and dry enough that it will begin as snow in the hours after midnight, and that a warm southerly wind will eventually push temperatures into the 40s and make for a rainy and breezy afternoon.

As for what's in between, the models say the Seattle area could get about 1-3" of snow before the changeover, while the Eastside might get closer to 2-3", and areas north of Seattle are still in the 2-4 inch forecast range with heaviest precipitation expected in the 6-8 a.m. time frame. (Those of you from Tacoma south and those west of Puget Sound are looking like 1" or so.)

In any event, any snow will be one of those 33-36 degree wet, sloppy snows with no freezing concerns. A Winter Weather Advisory is in effect from generally about 1 a.m. through late morning or early afternoon Friday, depending on your location, but it goes later the further north you are (8 a.m. coast/north Olympic Peninsula, 9 a.m. Tacoma/SW Interior, 10 a.m. Seattle, noon Everett, 1 p.m. Northwest Interior.)

But despite the models' insistence at the accumulating snow, there are a number of factors working against it -- namely we'll be getting a warm southerly wind with the front -- which is why the South Sound and coast are not expected to get much because you'll get the wind first. Also, it's really not all that cold out -- temps will be in the low-mid 30s tonight so already on the fringe -- and hasn't been cold for very long to really get a frigid air mass entrenched. Plus raw temperature indicators on the models suggest we're a bit too warm -- we usually like to see numbers a little colder before we buy into snow. That south wind ends up a bit stronger and the weak cold air mass surrenders quickly and we're left with a brief burst of snow then quick changeover to rain with little to no accumulation.

The National Weather Service summed it up perfectly in its 10:15 a.m. forecast discussion: "Everything else related to snow versus rain, snow accumulations, and start and end times remains in the Holy Moly Zone of Uncertainty." (Dibs on that band name.)

Raising the stakes: The computer forecasts have the peak time of snow during the heart of the Friday morning commute, which is why it's getting so much attention, so just be aware (if you aren't already) that there is potential for snow during the commute and that some schools may delay or close Friday.

If you are lucky enough to get some snow in your neighborhood and have been waiting two years to build a snowman, do it quick. Temperatures will rapidly warm as the south wind keeps blowing and by late morning or midday (if not sooner) we'll be well into the 40s with a breezy south wind gusting to 25-35 mph. By the evening commute, snow will likely be long forgotten.

Long range models keep us well above freezing for the next week.
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