Thursday, December 24, 2009

Boring Weather

Picture by Reid Wolcott of low clouds over the Puget Sound lowlands, taken from Newcastle Golf Course

How many ways can a meteorologists spell "Boring"? For the past several days we have been stuck in the classic mid-winter ridge pattern, when high pressure over the region produces dry, low wind conditions. The problem is that such conditions produce the hated, yes even despised, persistent low clouds and fog. Why? With a ridge there is a lack of clouds aloft and the surface can effectively radiate heat to space without the clouds getting in the way. The atmosphere doesn't radiate as well and the result is an inversion, with temperature increasing with height. Low wind speeds with the ridge result in a lack of good atmospheric mixing in the vertical, and thus a strengthening of the inversion.

Inversions act as barriers to air motion and as the air progressively cools near the surface, fog and low clouds can form. Moisture collects below the inversion, strengthening the fog. And wait! It is even worse than that! The top of the clouds are very effective in radiating heat to space....so you get cooling there, which mixes down into the cloudy layer. If the cloudy layer is thin enough, some sun can get through to "burn" if off. Fog burns off in two ways----from the outside perimeter towards the interior and from the bottom up. We didn't understand how fog burned off from its edges until weather satellites showed this to us. The burning off from the bottom results in fog "lifting" into stratus.

When there is fog around, Sea Tac is often enshrouded (and operations affected), while Boeing Field and Portland are operational. Why? Sea Tac is high--roughly 450 ft up---and when the clouds start lifting in the region, they can still be in the soup while Boeing Fields gets enough low-level cleaning to allow the airport to open. Portland has the advantage of air jetting out the Gorge...which can mix things enough to stop fog formation. In any case, it is always wise to fly as late as possible in the winter from Sea Tac, when fog is least frequent.

And when fog and cold are around, there is another threat to think about ....black ice on the roadways....so be careful.

Computer models indicate this general pattern should hold into next week. Not my favorite weather pattern. And one that doesn't improve our declining snowpack. Right now the snowpack is below normal for increasing portions of the region (see graphic)...and with El Nino effects strengthening after Jan 1, a little pessimism is in order for skiing and water supply.

15 comments:

LorbeerTLC said...

After last year this time, I welcome boring! LOL. ;)
Merry Christmas Cliff! :D

OffBeatMammal said...

while I love the fact it's dry at the moment I can't help wishing for a little snow to make the holidays feel truely festive...

Though if the rain stays away as well I can live with that

Chris Christensen said...

Just thank Goodness we aren't in Minnesota right now!

JewelyaZ said...

What a truly GORGEOUS photo!! Reid, could you please contact me... BellevueBlogMom@ Gmail.com... I would really like to feature this photo on the Bellevue City News Seattle P-I blog if you'll give your permission.

Thanks, and Merry Christmas, all. Much better this boring weather than day two or three of a long stretch without power due to a big windstorm, or day two or three of not being able to travel further than you can walk because of a big snow/ice storm. ;-)

jay said...

While Seatac is more foggy, planes can always land there as it has the navigational equipment to let aircraft land in visibility as low as 400 ft. Boeing Field however requires much more visibility. On a normal foggy day, the UPS and DHL cargo airplanes that normal land at BFI are diverted to SEA.

Upupaepops said...

I echo the sentiments

A STUNNING photo the colors and line truly splendid

I too would wish for just a small touch of "convenient snow"

but agree , after last year getting snowed in alone at home for Christmas, today is welcome

Tim said...

Actually, only certain aircraft can land at SEA when the ceiling is below 200' and/or visibility less than 1/2 mile. Those are CAT III conditions in aviation-speak, and not all commercial planes or crews are equipped for it. Alaska Airlines is all CAT III capable as far as I know.

HarrisonCZ7 said...

High Wind Warning East Puget Sound Lowlands -- any spillover for the Eastside - Bellevue, Issaquah?

RLL said...

That picture has got to be one of the best. Hope it gets a lot of publicity, maybe even sales? I could be interested.

C.P.O. said...

50 degrees in Bellevue right now? Must be the notorious mixing down from the strong easterly winds that is no doubt covered in the book.

Must read blogs said...

i really ENJOY this weather, its so FUN having to deal with my 15 yo's asthma that flairs up despite being on singulair, allegra and advair!

Kenna Wickman said...

Nice temps near Sequim yesterday afternoon with the winds heating things up. Would you believe - 57F along Discovery Bay???!??

mainstreeter said...

On This Day, December 27, In 1998, Nearly 18 Inches Of Snow Fell Along Interstate 90 At Snoqualmie Pass, Before Changing To Sleet And Freezing Rain. Up To Ten Inches Of Snow Fell Along The East Slopes Of The Southern Washington Cascades, And Up To Three Inches Of Snow Fell In The Kittitas Valley. Washington Department Of Transportation Closed Interstate 90 Through Snoqualmie Pass And Highway 2 Through Stevens Pass By Early Afternoon Because Of Aavalanche Danger, Stranding Over 9000 Holiday Travelers In Ellensburg And Cle Elem.

Christopher said...

I agree that as far as weather goes, boring is beautiful. Not very exciting for meteorologists, not much for Cliff to blog about, but I for one am thankful for no worries about power going out, getting snowed in, trees falling on roads and houses, etc.

Ah, for the boring weather life!

Reid said...

Thanks for posting the photo Cliff!

If you guys are interested in seeing more from that morning you can view the gallery (and order them!) here:
http://www.reidwolcott.zenfolio.com
that gallery is currently featured.

Cheers,
Reid