Saturday, February 28, 2009

Warm Front


You see the increasing clouds aloft...these are associated with an approaching warm front aloft...one associated with a vigorous offshore system (see sat pic). But that system..and its strong winds will not make landfall in the NW and strong winds will not reach our interior.
With low pressure offshore and high pressure inland, strong offshore (easterly) flow has developed west of the Cascades. So I would expect breezy conditions as one approaches the passes today--on I90 east of North Bend. The Seattle profiler shows the easterlies aloft...and such flow often produces warm temperature over the lowlands...so I expect temps in Seattle to surge into the 50s today.
The precipitation should hold off until this evening...so today should be a fine one, expect for some high and middle clouds. Then tomorrow we will see considerable clouds and some showers...and mild temps on the south side of the warm front (50s).
The weather pattern this week is a familar one..with a major low/trough over the Pacific (see sample upper level chart on Sunday). Low centers will spin up the coast offshore and most of the precipitation will head into California..where they need it. A boring collection of clouds and showers for us through Wednesday, after which the models indicate the chance of a cool down again. But I will wait before talking about that...

PS: For those interesting, I will be on KCTS on Sunday at 7 PM, answering weather questions (see link at right). Also I wanted to note the NW weather workshop on March 20-21st for those interested...it is open to all, but you should register in advance--but this does include technical talks (see link to right).

18 comments:

andycottle said...

Hey Cliff.... you mentioned about easterly surface winds today and temps getting into the 50`s. Despite some cloud cover, maybe the a few areas of the Cascade foot hills could come close to 60? I know that when we have easterly winds, the foot hills are usually the warmest. Or of course it can be the other way around and be the coldest with cold air coming through the mountain passes.

Also, it appears the 6z/12z NAM-GFS still show a prety good cold front come through here early pre-dawn Mon with showers after the front comes through. Are you thinking that it`ll be through here by sunrise Monday?

I`ll be watching your show tomorrow night as I`m sure there will be some interesting tid-bits about our PNW weather.

As for the cool down later next week that you and other folks who like to look at weather maps are seeing, it does look cool and unsettled and hope it brings some interesting weather.

inkprincess said...

I see on some 10 day forecasts that there may be snow Wed night/Thu night. Or so they say....and I hope!!

seattle said...

We are definitely getting strong-ish easterlies here in teh cascade foothills. It was exactly this way last weekend, also.

I understand that descending air is compressed and warms but wondered if anyone could answer why it should be warmer than where it started (i.e. in eastern WA). That is, the air starts out cold, rises and cools some more (as it travels over the cascades), then descends and warms back up. But shouldn't its temp just return to the temp at which it started (which was presumed cold)? We had a day in early feb where it reached the mid sixties in Monroe.

Also, in my experience strong easterlies indicate the approaching storm will make a more direct hit on western WA than the models presently indicate (I could be totally wrong about this though...)

-Somewhere in Sultan

andycottle said...

Seattle...

That is a good question to be asking us here.

Perhaps Cliff or someone else may have a better answer, but I don`t think the temp would return to it`s original state as the easterly winds are zipping through the passes at a fairly good clip. And with the air rising and cooling and then rushing back down, it`s doing as what you mentioned. It`s heating back up to due frictional force of the descending air mass.

Guess the example to use here is to think of an object like a comment falling toward earth. It`s going to be WARMER on the end falling toward us. And again, it`s due to frictional force as it`s entering earth atmosphere. So basically anytime you apply frictional force to something, you add heat at the same time. Not sure if my answer helps you out or not, but I gave a shot at it. :o)

Gator said...

I'm curious about Seattle's question, too. In studying oceans, we can look at conservative tracers like potential temperature and salinity to help identify a water parcel; it's possible origins, and whether it has mixed with other water parcels. Is potential temperature a comparable conservative tracer in the atmosphere? Are there other atmospheric tracers?

Jay said...

I can think of several reasons that the temp could get warmer on the west side of the Cascades during an east wind.

The descending air on the west side of the Cascades can become warmer that the east side temperature if there is condensation (clouds and rain) occurring on the east side. The condensing moisture adds heat to the air. I would expect this to be a rare situation, however.

Another factor is that eastern Washington is higher elevation than Western Washington, giving an addition rise in air temp as it descends to sea level, about 5 degree/1000 feet.

Eastern Wa can be under a temp inversion during east wind events, especially in winter. The mountain passes act like a dam holding back the cold air under the inversion, while the east wind picks up warmer air aloft, which then compresses and heats further on its way to western wa.

Cliff Mass Weather Blog said...

All,
This is a very good question. It doesn't have anything to do with friction or the other proposed reasons...rather it is because the air that descends into western Washington is NOT from the lower elevations of eastern Washington, but from mid levels where pressure is less. Thus, the air is warmed as it descends to higher pressure. If you study atmospheric sciences, you would learn about potential temperature...the temp air would have if it descends to 1000 mb pressure (roughly sea level pressure outside of the mountain). Potential temperature actually increases with height...cliff

windlover said...

Left home around 7:00 pm...a little chilly (in the 40's) and just a little breeze....came home around 9:30 pm to a 55 degree temp with winds sustained at 15 mph, gusting to 35. wierd!

Kevin Purcell said...

And if you don't have a decent atmos sci text then Wikipedia does OK

http://en.wikipedia.org/wiki/Potential_temperature

Another thing to keep in mind is EA WA isn't at sea level either. Take a look at a topo map.

Gator said...

I'm looking forward to Cliff's appearance on KCTS9 tonight at 7pm.

In addition to Cliff's book, does anybody have recommendations for 101 textbooks in atmospheric science?

Also, are there tracer molecules/characteristics that atmospheric scientists use to track air parcels? In oceanography, conservative tracers are used to track currents and also answer all kinds of other cool questions. I'm guessing that since the atmosphere is so ephemeral that tracers may not be applied in an analogous way, but still possibly useful.

Thanks, Jeff

mainstreeter said...

I had a book called Introduction to Meteorology or Meteorology Today, which I think is still in print, probably several editions later.

mainstreeter said...

I think it's Meteorology Today, really high priced now.
http://www.amazon.com/Meteorology-Today-C-Donald-Ahrens/dp/0495555738/ref=sr_1_3?ie=UTF8&s=books&qid=1235965924&sr=1-3

But the college books stores sell used copies too.

letshavefun1536 said...

Cliff, can you stop continuing to tell people here on your show that drizzle and clouds are gloomy and bad? Gee, let people make their own decisions.

Teresa said...

Okay, I've been watching Cliff on KCTS, and I'm not sure I'm happy to hear that for every 5 seconds between seeing lightning and hearing thunder, the lightning is ONE mile away.

I always thought it was a mile per second....now I'm going to be more afraid of the lightning than I was.

Oh well, sigh ;-).

I'm enjoying the Questions and Answers.

Teresa in Sammamish

Richard Berndt said...

I enjoyed the KCTS special - the question and answer format worked well. Having you control the graphics with your Mac worked well, also.

I did think that KCTS did put you in an odd time slot - sandwiching the show between gospel and Doo-Wop shows was strange. KCTS should have your next show as a lead-in to NOVA or something more compatible.

andycottle said...

I liked your show as well, Cliff. Very interesting. And to hear of the lenticular clouds being UFO`s? LOL! But hey, I can see it being mistaken for that very reason. Those are one of the coolest clouds around and is perhaps the only type of clouds seen here in the Western US.

I know KCTS is doing their part to sponsor public tv, but I was really expecting it to be all Cliff with no 'breaks' in between question/answer segments. Hope to see more of ya on tv when time allows! :o)

Harrison said...

Lots of rain here in Spokane. It's 37F and raining very hard. Most our snow has melted off, which is nice, but the city looks awful. Since Jan. 1 many areas in Seattle have seen much more snow than Spokane. Spokane has been relatively dry and foggy, if not soggy in between (but not snowy) It's as if winter visted for 2 1/2 weeks and then left...hmm

Teresa said...

Cliff, please give more information about your Seattle Center talk.