Cold Air Moving In

February 24, 2011

Real calm weatherwise this evening…the calm after the “storm” I suppose.

Cold and dry now as the last flurries seem to be just about gone on radar and east wind is picking up across the Metro area.  Our dewpoint just dropped about 5 degrees in the last hour at the station.  We’re freezing up nicely across the region as the modified arctic airmass moves in.  The low dewpoints will help dry out roads, so I don’t expect a major huge mess for the morning commute; just areas of ice and some leftover snow on the hills or shady spots. 

I’m really looking forward to the sunshine the next two days.  Though it’ll be chilly (and breezy tomorrow), it’ll be nice to be blinded by the bright late February sun.  Speaking of calming wind, perfect radiational cooling should drop us to right around 20 tomorrow night.  No snow cover to help for most of us after another sunny day in the 30s, but it’ll still be unusually cold for this late in the season.

I’m keeping an eye on the transition into wet weather…appears to be Saturday evening or night as precipitation arrives.  Good chance of a snow start with real nice evaporational cooling, but southwest wind picking up during the night means it can’t last that long.  There is not dry/cold air coming in from the east at that point.  In those situations it’s usually not a significant snow event.  I also notice the precipiation amounts are quite light for the first 12 hours; that doesn’t help if you want snow either.  The main message is that it doesn’t look real exciting right now, we should wake up to rain on Sunday morning.  At best rain with some leftover snow melting on the ground.

I’m also keeping a close eye on a deep low forecast to move north up the coastline late next Tuesday.  The last two runs of the GFS have been impressive, especially the latest at 00z.

In general, as March begins, we’re heading into classic La Nina early spring conditions; cool and wet.

Here are the snow total maps from today…click for a better view.  Notice how Clark County had more than the top of the West Hills!

Stay warm!

Chief Meteorologist Mark Nelsen


Midday Break, Then Evening Flurries/Freeze

February 24, 2011

The official total from the overnight/morning snow at the National Weather Service Forecast Office was a huge….0.7″  For those math-challenged, that’s about 3/4″.   Still the biggest snow of winter season…on February 24th!  And that total may rise this evening…maybe.

BUT, we have a Snow Totals posting here on the blog plus Facebook and it’s clear that official total was the low end.  Generally the inner/eastern part of the city had less than 1″.  But lots of SW, W, E, and Clark County had 1-3″ (almost everywhere else).

BETWEEN NOW & LATE AFTERNOON:  Pretty quiet.  Late winter sunbreaks, temps up around 35-37, plus just a few scattered snow showers means good driving conditions. 

THIS EVENING:  Could get messy again for two reasons:  Cold air moving through the Gorge will spread into the Metro area, freezing everything up at some point after dark.  EVERYTHING will freeze in all areas.  At the same time our models show a possible burst of snow showers.  So another Trace-1″ is possible during this time anywhere.

TONIGHT:  Hard freeze, but clearing skies…25  This means roads will be icy for GDO Friday AM, but blue skies.  Another snow day or two hour delay for lots of schools.

FRIDAY-SATURDAY:  Mostly sunny, but chilly…35-40 degree highs.

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The above note is what I just sent out to our newsroom folks.  Looks like another long day today with real sparse showers and sunbreaks keeping temps above freezing at least through 4-5pm.  The good news is that the south wind is gone, gradients are now flat in the Valleys and easterly through the Columbia River Gorge.  I see the dry arctic air is moving through the Gorge this morning, and the WRF-GFS plus our RPM both show it arriving by 4pm at Troutdale and spreading through the entire Metro Area soon after dark.  That’s at the surface; above there will still be the last of the showers rotating through our region.  Models seem so be hinting (WRF-GFS and our RPM) that the colder air arriving below will give us one last lift to the showers.  So I’ll say another Trace to 1″ anywhere around sunset or just beyond before the moisture runs out.  Otherwise little/no accumulation during the daylight hours with those forecast highs around 37.

Chief Meteorologist Mark Nelsen


Snow Totals Thursday

February 24, 2011

How much snow did you get (so far?).

1. Total

2. Location

3. Elevation (if you’re above 500′)

This is for snow totals only, KEEP WEATHER DISCUSSION IN OTHER POSTS.

Mark