“Storm” Thoughts

November 29, 2006

As I mentioned earlier, National Weather Service has a Winter Storm Warning out for the metro area for late tonight through tomorrow morning.  My thoughts haven’t really changed much since last night’s post.

1.  Nice cold air over us, but not as dry as with our last few ice storms, so evaporational cooling won’t have as strong an effect (temps won’t dip much with start of precip).
2.  That dip in temp with precip may easily be countered by increasing southerly wind by midnight.  This is very different than when a normal ice storm starts and 70 mph wind are gusting out of the Gorge.  For example, we usually get gusty east wind here at the station at the beginning of ice storms.  That’s due to the easterlies coming down off the West Hills.  It’s calm here right now.  So I wouldn’t be surprised if at 6pm we are at our lows for the night.
3.  If so, then only spots close to the Gorge or in the hills will get freezing rain at the beginning.  Forget west of the West Hills, north of Hazel Dell, or south of a Downtown PDX-Gresham line.
4.  Cold front passes through around 4am.  A sharp switch to SW wind with this EVEN IN THE GORGE means a jump to a well-mixed atmosphere with a 4,000′ snow level.  That pushes metro temps into the low-mid 40’s by daybreak!  Hard to believe with this cold of air over us now, but I see no good reason to doubt it.
5.  As for snow…maybe briefly at the beginning, but seems unlikely with such strong warm advection above.

I don’t think this warrants a Winter Storm Warning in the metro area, but maybe in the Gorge.  I’m not sure why the NWS doesn’t just issue a Freezing Rain Advisory instead.  Maybe because snow or sleet could be mixed in?

Very simple forecast beyond tonight’s…ridging or split-flow through the foreseeable future.  What a dramatic change that follows the calendar….wet November to dry December?  Mark

UPDATE 11PM:  Moving in quickly now…but the Portland Radar died at 9pm!  Nice timing.  Looks like temps will stay about where they are.  If you are 32 or below, you’ve got ice in the next hour.  Drive carefully!  By the way…excellent timing by models…10pm to 1am arrival time right on.


Brief Comments

November 29, 2006

Just a brief post at mid-afternoon.  I’m going to wait until after 5pm to post again (after my busy schedule dies down and the early evening TV forecasts are already made).  I see the NWS has issued a Winter Storm Warning now for the metro area…isn’t that interesting…

Nice chilly airmass overhead.  PDX is only 34, easterly flow coming out of the Gorge at Corbett is only 27 degrees at about 700′.  Dewpoints are way down too.  Unfortunately PDX-DLS gradient is a weak 4 millibars, hardly ice storm material there.  This would seem to support snow or freezing rain tonight when precip begins sometime between 10pm and 1am.  But maybe not?  I’m making the forecast right now and I’ll be back in a couple hours.
I DO notice that Salem and Kelso are probably already out of the "danger zone" with 36 and a dewpoint of 29 (or 28 at KLS).  That is too warm for freezing rain even with evaporative cooling when the precip starts.  That doesn’t even account for warming from a south wind by midnight in both spots.   And forget about cooling tonight, we’ve got solid cloud cover overhead…Mark