Tuesday, March 8, 2011

Cold and Wind

Look at the temperatures over the past four weeks: Today, was the first day since mid-February that we reached the normal high....three weeks! February was the seventh coldest at Sea-Tac since 1948. I suspect that if we looked at the period from Feb 15 though March 7th, it would be in the top three cold years at this location.

A series of storms is now on tap and the first one is off our coast. Here is nice infrared satellite image this evening. Infrared (IR in the business) pictures tell us how much infrared radiation the earth and clouds are radiating in a certain wavelength range in which the atmosphere is relatively transparent (called a window region). For IR images the wavelengths observed are typically 10-12 microns.

Cold clouds are shown as white, warmer objects dark. Since temperature usually decreases with height, cold clouds are generally high and vice versa, so we can tell the height of clouds with such imagery.

You see that well defined hook? The low center at the surface is right in the middle of this. And the cold front is associated with the long narrow cloud feature extending to the south.

This low center will move up the coast west of Vancouver Island..so no major windstorm here.... (see graphic for pressure pattern at 10 AM tomorrow)...

but there is another behind it for Thursday and this one is coming in much closer. Strong winds are in the cards with the next system. Remember the general rule of thumb: to get strong winds over Puget Sound the low center must cross the coast between the NW tip of the Olympic Peninsula and the middle of Vancouver Island.

6 comments:

Dave Eriksen said...

"Remember the general rule of thumb: to get strong winds over Puget Sound the low center must cross the coast between the NW tip of the Olympic Peninsula and the middle of Vancouver Island."

Geez! So damn obvious, now that you said it. Typical "Mass-ism." I remember providing A/V support for you, back around '82, for one of your Intro classes held in Kane Hall. You really had the knack for cutting to the quick of a clear explanation even back then. Some things never change...

Ferdi said...

So far March's weather isn't looking too benign. At least with this pattern the islands get some rain shadow relief. It is interesting how the average temperatures for the period from the middle of February to the middle of March do not rise appreciably. March is almost as cold as February and often more cloudy.

Donna & Chris said...

Just experienced a bit of a serious deluge in Fremont!

thomas said...

What would happen (wind)if the low center passed over central Puget sound?

Steven said...

I was just wondering if anyone has ever studied the idea that you can gauge what the summer will be like by the strength of the spring equinox storm?

Wx Enthusiast said...

February 15 - March 7 was the fifth coolest such period at Sea-Tac. Cold? Hardly - average temperature of 38.0 F. The years with the four cooler such periods were 1955 (34.8 F), 1956 (36.1 F), 1951 (36.8 F), and 1960 (37.5 F).