Snowflakes fly, but no need to consult 'snow panic' manual

Snowflakes fly, but no need to consult 'snow panic' manual
Snowflakes fall off Lakemond Blvd. in Issaquah, March 8, 2010.
SEATTLE -- OK, admit it -- you were at least peeking at the "snow panic" manual hidden underneath the coffee table.

You know, the one that gives protocol on how fast to drive to neighborhood food stores to stock up on potato chips and doughnuts (because calories don't count in a snow emergency) and raid the sterno aisle as you make sure to keep your arms raised above your head and sway side-to-side as you yell in panic, "I saw a snowflake on my windshield!"

Yes, for the first time since mid December, we're seeing a few snowflakes fly in some spots around the Puget Sound area. Snowflake reports have come in from the greater Tacoma area, Bellingham, Oak Harbor, Federal Way, Shoreline and even the U-District. And I guess we can be forgiven a little excitement since at this point, Houston is still ahead of us this winter in the snow accumulation department (1"-Trace, if you're keeping score.)

But I think when all is said and done, Houston is still going to remain in the lead, as this event is really nothing special, meteorologically speaking.

Some cold air moved in Sunday in the wake of our first true "cold front" since it seems Clinton was president. The air itself isn't quite all that cold -- we're mainly hovering in the low 40s, but there are two key ingredients hanging around that are conspiring to bring some snowflakes -- a few moderate showers and some dry air.

Those two can combine together to temporarily drop the temperature 5-6 degrees and get it at least close enough to the mid 30s to get us a fringe snow where these showers occur.



Here's the deal: It takes energy to evaporate water. When a passing shower moves into an area where there is dry air, the precipitation falls and starts to evaporate since the dry air can hold more moisture. However, evaporating water requires heat and energy. As more and more drops evaporate, the air is using up more of its heat energy, thus making the air cooler.

The heavier the shower, the better this engine can get going, and the cooler the air can become. This is how if you look at a city's observation and it says 42 degrees, it can still begin snowing a short time later, if the air is dry enough.

A good example this morning is at Tacoma Narrows Airport, where it was 41 degrees at 9 a.m., but with the dry air around, a shower dropped the temperature to 36 and it was just enough for snow. Compare to a shower that moved through the same area at 1:30 a.m. when it was 39 degrees, but the air was much more humid then, and thus that cooling engine didn't get going and it was a simple rain shower.



We don't have much moisture running around here today for a widespread event -- what we're dealing with Monday morning were a few lingering showers and a weak Puget Sound Convergence Zone. (See video of it in action here.) So a vast majority of us won't see anything - in fact, there's decent amount of sunbreaks out there too.

More unstable air is moving in this afternoon that could trigger some more showers in the afternoon that could briefly be this fringe snow type stuff, but accumulations will be light and brief with no road problems expected, and the temperature will bounce right back up to near 40 after these showers pass as the cooling engine ceases, and the snow will quickly melt.

These showers can also bounce back and forth between snow and rain as the intensity of the showers increases and decreases and with it, its ability to cool the air.

The showers end by overnight, but clearing skies will allow temperatures to plunge below freezing in many areas. In the outlying areas, lows are expected to be in the mid 20s while near freezing is expected in the city areas.

Thus, while snow itself isn't of much concern, anywhere where the roads get wet could be icy Tuesday morning, so definitely factor that in to your Tuesday morning commute and have some contingency plans if your school delays an hour or two.

Latest forecast models take our next storm and not only slow it down, but push the bulk of the moisture farther south. So while it might be a rainy day on the coast, the inland areas are now looking like they'll be dry, possibly all the way into Tuesday night. Some models continue to show a chance of some light snow accumulations right along the western Hood Canal area in that snowbelt by Brinnon/Hoodsport and Shelton, but accumulations are expected to be 1-2" at best. The rest of the area is dry.

The cold air is gone by the end of the week and we're back to just regular ol' rain showers. So feel free to tuck that panic manual back away under the coffee table and perhaps switch that store order to bagels instead of doughnuts :)