Winter (still!) stubbornly clings to throne

Winter (still!) stubbornly clings to throne
Snow in the Smokey Point neighborhood taken Saturday, March 29, 2008.
It didn't get much of anyone out of school, but at least it didn't turn the freeway into a skating rink.

The snow Friday wasn't quite as accumulative as expected, but just about everyone got to at least watch it snow for a while. And just for good measure, snow returned again to some areas Saturday morning, doing a better job of leaving an accumulation, but over a much smaller area.

That marks the fourth day in late March dealing with snow in Western Washington -- a pretty major feat!

Also a major feat? Keeping temperatures in the 30s for most of the day. Believe it or not, Minneapolis was actually warmer than Seattle Friday, reaching 43 degrees while Seattle only reached 42.

That 42 degrees set the record making it the coldest high temperature for March 28th, breaking the previous record of 43 degrees.

As for the snow, that is not a record. We've had a lot of people ask if this is the latest snow, but it's snowed way later than this before. April 17, 1972 holds the record for latest snow at Sea-Tac Airport, getting 1.2" that day. That must have been some winter, because October 27, 1971 holds the record for earliest measurable snow.

The snow Friday wouldn't have counted anyway since it didn't accumulate at Sea-Tac Airport, but a few spots with a little elevation got anywhere from a dusting to 1/2".

As proof, a nice little snow shower moved through the Tacoma and University Place area just after noon Friday. (See video at the right submitted via YouNews)

The higher elevations of the Hood Canal area were the snow winners, with reports of 2-3" above 200 feet around Hoodsport and the like. But almost everyone else was an inch at best.

No major problems were reported due to the snow, unless you count decreased office productivity from people staring out the window.

And believe it or not, snow continued into Saturday as well. Saturday's winners are Skagit, Whatcom County and northern Snohomish County, where a nice, large cell developed and brought a decent coating of snow to the greater Bellingham and Smokey Point area, to name a few.

Those areas could see as much as 3" by the time this cell passes.

For the rest of us, it'll be crossing our fingers for snow fans. The widespread snows are over as the main area of low pressure has moved away, but the atmosphere is still very cold and unstable, so we'll see these random rain or snow showers popping up and roaming about.

As we're seeing Saturday morning, if one of those showers gets over you, you could see a little accumulation, but as we get into the midday and afternoon hours, it'll become more difficult to snow as the temperatures rise over 40, with snow reserved for the heaviest showers or above 500 feet. In between the showers, the sun will be out, so really quite the mixed bag.

But snow levels will drop again this evening and tonight as the sun sets. In addition, satellite photos show a very weak disturbance passing by, which could enhance the showers running around this evening. So showers look to become more frequent and be able to be snow to lower levels -- perhaps sticking to grass as low as 300 feet. Again, roads shouldn't be much of a problem in the evening and early night hours because their surfaces are warmer until deep into Saturday night.

Overnight low temperatures will again drop to right around freezing, thus bringing at least a chance for some icy spots early Sunday morning.

As for Sunday, it's looking like we finally get this out of our hair. There might still be a lingering shower or two roaming around, but generally partly sunny and warmer -- at least upper 40s.

Early next week we turn the calendar to April literally and figuratively as the weather goes much sunnier and warmer. (Well, not too warm, but relatively warmer.) Highs could reach the mid-upper 50s by the end of the week.

So, office productivity isn't looking much rosier then either, but probably because half your office will be on the ski slopes.

HOW COME IT SNOWS LOWER THAN THE GENERAL SNOW LEVEL?

So I've just finished writing about how snow levels are generally 500-1,000 feet. So then, how is it possible to still snow near sea level?

If the intensity of a passing shower is strong enough, it can artificially lower the snow level a few hundred feet through a process called evaporative cooling.

When snow first begins to fall into drier air, that snow will evaporate. But the process of evaporation takes energy. Sapping energy from the air causes it to cool, dropping its temperature. So as this process churns away, the temperature will drop, but the humidity will rise as you add more evaporated moisture to the air content. The drier the air is at the beginning, the farther the temperature can fall during this process. (This is also known as "wet bulb cooling".)

But wet bulb cooling needs some help, and that brings up the second factor: precipitation intensity. We need to have a decent amount of oompf in the precipitation to get that cooling engine going. If it's a really light snow or flurries, it won't evaporate as much or as quickly, which means this cooling engine won't be very efficient and the temperature may not drop as much.

On the other hand, if you get a really heavy snow shower, that can really get that evaporation going and drop the temperature quite a bit. This is typically how snows in the Convergence Zone work when it snows in Everett/Lynnwood despite being in the low 40s across the rest of the region. The snow along the Hood Canal usually benefits from this as well.

That's what we're looking at in these snow scenarios the rest of this week. The one thing about this process is once the precipitation ends and the cooling mechanism goes away, the snow level usually quickly rises back to where it was before, and the temperature near the ground will rise.

Thus, it's not uncommon for the fresh-fallen snow to quickly begin to melt. And that's what we expect with these snow scenarios. Any snow that does fall should begin to melt as soon as the snow stops, as the general ambient temperature is expected to remain above freezing. The exception to this is area above the 500-700-foot snow level at night, where snow could stick around a little longer.