Evening Update; Wind and Disappearing Cold Spell

November 16, 2011

Nice surge of wind just ahead of the cold front this evening, our first 40 mph wind gust at PDX since mid March.  Winter can’t be too far away!  Wind continues but gradually decreases after the cold front passes in the next hour.  Note it went from SW to W at Astoria when the front passed.

No change to my thoughts about Friday evening or early Saturday morning in the previous post, but now models are showing a much quicker switch back to southerly low level flow and very little dry north or easterly wind over the weekend.  As such I bumped up low temperatures farther.  By Sunday we should be back into the upper 40s.  Too bad, because I’ve been looking forward to some crisp and clear weather over the weekend.

Chief Meteorologist Mark Nelsen

 


Thoughts on Lower Elevation Snow

November 16, 2011

A few intriguing changes in the meteorological models this afternoon, so here are my updated thoughts on the possibility of low elevation snow the next few days.  First, for those that want the basics:

  • We can pretty much rule out snow in the lowest elevations through at least Friday afternoon now.
  • IF we get some sort of sticking white stuff down below 1,000′, it’ll happen sometime between the Friday evening commute and Saturday morning.
  • Right now I’d say a dusting is looking a bit more likely on the hilltops around 1,000′ maybe Friday evening and/or Saturday morning.
  • Quick warmup Sunday and beyond…very wet and windy at times next week
  • A hard freeze doesn’t look likely, maybe upper 20s here in the city either Saturday or Sunday morning.

Forecast for tomorrow is easy, strong and colder westerly flow coming in off the Pacific spells heavy snow in the mountains.  Our RPM shows 20-25″ by the time we get to late Friday, most of that falls late tonight through tomorrow night.  Snow levels drop suddenly with a secondary cold front coming through NW Oregon in the middle of the night, probably hanging right around 2,000′ through tomorrow afternoon.

Tomorrow night the snow level drops a bit further, down to around 1,500.  But then moisture appears to shift mainly to our south by daybreak on Friday.  Or 18z RPM shows just a few hundredths precipitation from late tomorrow night through Friday afternoon.   The other mesoscale model I rely heavily on, the WRF-GFS from UW, shows the same thing.  In fact they would both imply a partly cloudy day with just a few sprinkles Friday.  That combined with a continuing light southerly surface wind gives me more confidence that nothing interesting is going to happen Friday morning. 

During the day Friday and Friday night, a surface low moves from NW to SE from off Vancouver Island down to around Coos Bay, then pivots across Central Oregon.  This CAN sure be a good snow pattern for us as surface flow turns easterly.  So here’s the new wrinkle:  Some showers are shown on our RPM and WRF-GFS as the backside of the low moves by.  Our model implies a burst of showers as the sun sets Friday night.  The WRF-GFS just shows a smattering of showers around.  Something to watch closely.  And I think this increases the chance for at least a dusting of snow down to around 1,000′.  I should point out that in general models have warmed slightly.  The 12z GFS and ECMWF don’t show 850mb temps below -6.  And the 18z NAM is slightly warmer with temps staying above -6 now.  A minor detail, but significant that they don’t show it getting any colder.  I like to see a -7 or -8 with onshore flow to see sticking snow down to lower elevations.

On Saturday there is no significant change as a 2nd stronger surface low dives SE and offshore heading for Northern California.  Our RPM shows some of the stratiform precipitation making it all the way up over us by 10am Saturday; I think that may be overdone, the WRF-GFS keeps it farther south.  Once again though…something to watch closely. 

Another trend is for a quicker warmup Sunday and beyond.  850mb temps are already warmer by Sunday morning and southerly low-level flow is here by late Sunday already.  Due to that I bumped up overnight temps a bit over the weekend, and raised high temps slightly too.

Chief Meteorologist Mark Nelsen


Pathetic “Storm” So Far…

November 16, 2011

Yikes!  Sad precipitation totals so far and the radar is not looking impressive at all.  That ZERO at Hillsboro is a bit suspect, since even the driest locations west, south, and just east of there on the MADIS network have had at least .13″.  Here at the station (5 miles east of HIO) we’ve recorded .17″  Another disappointment is the very slow to appear southerly wind.  Funny that the 58 mph at Crown Point earlier is just about the strongest in the state so far, although I’m sure a few exposed coastal locations will still see the wind gust up around 60.  Definitely not a High Wind Warning worthy event for sure.  I’m finishing up the forecast and will have my latest thoughts on snow possibilities in an hour or so.