Tropical Temps!

December 20, 2005

So close, but yet so far from warmth!

I’m on vacation now back in a frozen heck of a place (Corbett), but how about those temperatures on the Oregon Coast this morning?  If only we get our winds switched around to southerly at some point we’ll jump up close to 60.  I noticed Tillamook was 66 at daybreak before the wind went back to easterly.

The layer of cold air is only about 1,200′ deep now in the Western Valleys.  I live at 1,000′ and it’s finally up to 33 degrees and the ice is beginning to melt.  Last night’s drive was rough, but 2 years ago was much worse.  Maybe the worst was the 2 mile long line of trucks chaining up near Wood Village on the freeway. 

Also interesting this morning was the wind at TTD (Troutdale).  Check out this observation.

Notice how the wind sensor "broke free" from it’s ice at 2am?  Did any of us really believe it was only blowing 17 mph last night?  Turns out it was gusting close to 50 still.  In fact at one point yesterday evening all wind sensors at the west end of the Gorge and east metro were frozen up.   The PDX-DLS gradient was over 13 millibars though, which should have produced 70mph gusts east of TTD.

Okay…now I’m really on vacation…have a good Christmas!

And it Ends…11am

December 19, 2005

What a difference 2 degrees can make!  Over 3/4 of the metro area escaped any significant icing this morning.  It was really confined right around the entrance to the Gorge by 8am or so (Troutdale/Camas/Washougal).  During the morning rainfall, temperatures were right around 32-34 degrees from Hillsboro to Portland to Vancouver.  Obviously the "evaporative cooling" mentioned in my last post just didn’t drop the temperature more than a notch or two.

So I guess this ended up as the storm that was 2 hours early and 2 degrees too warm.  Ahh, the devil is in the details.

Of course temperatures aren’t exactly skyrocketing, that’s because the easterly flow continues…pressure gradients are still over 11 millibars through the Gorge at midday.  The only reason it’s warmer is the air over us has just warmed those few degrees.

An Ice Storm continues from Troutdale east into the Gorge through tomorrow morning.

The airmass above us is warm enough to support 55 degrees here in Portland (Newport hit 57 early this morning), but we have to wait until probably Wednesday to get temps well up into the 40’s.  No good south wind until that time.

Now the Freezing Rain…11pm

December 18, 2005

A quick changeover this evening to freezing rain.  I noticed a sensor at 2,000′ east of Silverton went from 24 to 43 in just a couple hours this evening.  As I mentioned on the 10-11pm shows, temperatures are a few degrees warmer than the ice storm last January, so now I’m thinking the surge due in at daybreak will be it.  Although models say it could contain up to .50" rain…that’s a lot of ice!  After that we should gradually warm, but of course the Gorge (east of Troutdale) should remain near or below freezing through later Tuesday.  There is no good westerly, warming wind through the Gorge itself until a system passes by to the north Thursday.

By the way, I made brief reference to "evaporative cooling" on the show, although I didn’t use those words.  Here’s a better explanation:  As rain or snow falls into a dry airmass, some of that moisture evaporates.   But to change a liquid back into a gas (water vapor), it takes heat, which comes out of the air.  So basically the temperature drops until it meets the dewpoint and the dewpoint rises too.  If the temperature is 35 and the dewpoint is 20…when precipitation falls through it, the temp may drop to 31 and the dewpoint comes up to 30.  That’s called evaporative cooling.  It happened when the snow fell today and should happen again when the heavier rain arrives near daybreak (or else the forecast busts and we get mainly plain rain).

It Has Begun…5pm

December 18, 2005

Well, now we know when the storm will arrive…about 2 hours earlier than expected.   Looks like lots of you cut it a bit to close today!  Drew mentioned around 4-5pm for a start, and it seemed to start around 2-3pm instead.   I couldn’t believe how many folks were at the local stores as it was beginning.

As of 5pm we have made it through one wave.  The next may not arrive until close to sunrise.  That one should be quite a bit warmer above and very wet.  I expect a lot of solid freezing rain with that one.  Forget the morning commute if you have a choice.

Wind should taper off (at least to regular windy instead of crazy windy) overnight after this first wave finishes going by.

Proceeding According to Plan

December 17, 2005

I’m not working tonight, but inbetween family duties…weathergeekness calls!  Amazing how well the models are handling the first system, basically falling apart over Western Oregon this evening.  So no reason to doubt steady freezing rain or ice pellets arriving as Drew said around sunset Sunday from Salem-Longview (earlier south).  We can’t rule out snow briefly at the beginning, but ice pellets are far more likely.  Significant snow accumulation is likely east of Multnomah Falls in the Gorge.

By the way, the peak wind at PDX today was East 52 mph, which is the strongest wind gust in 4 winters (at the airport).  The wind will die down some tomorrow everywhere away from the Gorge, but pick up in the Gorge dramatically by morning.  This seems to happen with every ice storm.  A non-scientific way of thinking of it is that as warm air moves in above, that moving layer of air through the Gorge is squeezed down into a smaller area.

I am a bit concerned about the amount of moisture coming…it’s looking wetter than last January’s storm and slightly colder.  But not nearly as cold as 2 years ago.  So we think it’ll stay solidly frozen across the entire metro area through Tuesday AM.  And even by Tuesday PM, freezing rain may still be an issue right near/in the Gorge.  By the end of that time there could be some pretty good glaze accumulation east of I-205.

One more note, Drew Jackson, our weekend meteorologist is one of only 3 forecasters in Portland who grew up in the area (I would be #2).  He knows the weather patterns here well, so pay attention to him when he’s on…he does a great job keeping on top of things.  In fact we almost always come up with the same forecasts in situations like this.

A wet and/or mild Christmas is now guaranteed, so enjoy the "silver thaw" while it lasts.

I’ll begin updating this regularly once the storm starts…Mark

Ice Storm Coming II

December 16, 2005

Satellite really shows us "in the squeeze" tonight as a fresh batch of cold/dry air is surging west across the Rockies into Eastern WA and moisture approaches from the SW.  We are in the middle, which is a classic ice or snow storm setup!  00z models have really come into agreement for no precip from system #1 Saturday night, but all have precip in here after sunset Sunday.  Not a lot, but that all day ice storm last January?  It only produced .17" of "rain" at PDX!  Doesn’t take much to make a mess when it’s freezing rain. 

We will probably not get above freezing Monday.  It’s a common error to bring the temp in Portland above freezing in the first 24 hours of an ice storm.  Very unlikely with air this dry.  As moisture falls into it heat in the atmosphere is used for evaporating the moisture.  For example, if it’s 32 with a dewpoint of 16 when the precip  starts Sunday evening, the temperature will probably drop to 27 and the dewpoint comes up close to 27 as the air saturates.  Then it takes a long time to raise the temperature 5 degrees as cold air continues to pour out of the Gorge.  It happens every time.

As mentioned last night, short term issue is cold and especially wind.  Speaking of "the squeeze".  PDX-DLS gradient is over 10 millibars this evening, and I would expect a 13-14 mb gradient Saturday night and again Sunday night.   This pattern in the past has produced 80+ mph winds at the west end of the Gorge, while it’s almost calm across 2/3 of the metro area. 

And just for you Longview folks:  Probably freezing rain or maybe briefly snow Sunday evening, then a change to rain by Monday midday.  High Monday near 34.

Columbia Gorge Ice

December 16, 2005

I took these nice pictures this afternoon at Latourell Falls.  Those are the first falls you come to after Crown Point on the old scenic highway.  I highly recommend a visit this weekend if you get a chance.  Some winters it never gets this cold so the falls don’t always freeze.  I’m working on the forecast and will have a fresh entry this evening.Dscf0011_5 Dscf0010_4