ECMWF Monthly Run

December 19, 2013

The 4 weekly maps from last night’s ECMWF run show some sort of ridging wanting to remain just off or along the West Coast through the next 4 weeks!  Not a good sign for those wanting some weather action in January.  But just one run of one model of course.  Enjoy the pretty colors:

500za_week1_bg_NA

 

500za_week2_bg_NA

 

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12 Hours Away: Areas of Snow & Ice Pellets For A.M. Commute

December 19, 2013

7pm Thursday…

There are no watches, warnings, or advisories for late tonight and Friday morning, but anyone up and around in the late night and early morning hours may see either snow/sleet.  Either in the air or a dusting on the ground; this MAY end up just being a “conversational snow”, as we like to say, for a good chunk of us in the metro area.

Something should start falling out of the sky sometime between 3-7am.  It’ll start as snow; temps will be right around freezing, maybe slightly above.  Then right around sunrise warmer air moves in above, which means ice pellets (used to be called sleet)  are more likely.  That’s when snowflakes melt into raindrops up above and then refreeze into little chunks of ice before they hit the ground.  It has a “clinky” sound when it hits.

By 8am, the atmosphere will be too warm to support anything frozen since the freezing level will be jumping up to 8,000’.

The Highlights

  •  A brief “wintry” mix between 3-8am.  A dusting is possible anywhere from the metro area to Longview down to the valley floor.  But not everyone will get it.  It’s real light.
  • Snow to sleet, then probably straight to rain.  Freezing rain looks unlikely since temps won’t drop much below freezing (if they do).
  • Some areas may see sleet/snow on roads, depending on the temp.  Best chance would be West Hills, central/north Clark County, Scappoose/St. Helens, and Banks/Vernonia.  Those areas also have the best chance of seeing actual freezing rain at the end of the event around 7-9am.
  • It’s all over after 8am for just about all of us.
  • Gusty south wind tomorrow afternoon, maybe gusts 30-35 mph as temps climb into the 40s.

What We Don’t Expect

  •  A snowstorm; not enough moisture for more than 1-2” of snow even if it did that the whole time.
  • An ice storm; again, just not a whole lot of anything.
  • Widespread frozen roads and a hellish commute.  Probably not cold enough or enough moisture.  Different story up north as mentioned in the highlights
  • More than ½” for 90% of us in the metro area
  • Snow/ice pellets south of the metro area (Salem/Albany) or at the coast.

Here is the latest from this evening’s run of our RPM showing a changeover from snow to ice pellets already at 6am spreading west to east across the metro area

rpm_6am

Then at 9am all frozen precipitation is over in the lowlands unless freezing rain/ice pellets holds on up in northern Clark County.  And, actually it looks mainly dry at that time anyway.

rpm_9am

I’m getting the feeling that Amboy, Yacolt, and Battle Ground are the places to be for this event.  And finally the snow total graphic showing the main accumulation “action” in Clark County:

rpm_snow_9a

The evening NAM model has snow a bit farther south and west into the middle of the metro area.  This is snow accumulation from 7-10am.

nam_snow_10am

The sounding is definitely all snow through the 7am hour.

To wrap it up, here are the percentages I assigned to each of these events…

MarkSnow_PortlandOutlookPercentages2

By the way, for those of you that work the late shift and wake up around 9am like me?  You’ll miss the whole thing!  Go ahead and sleep in.

Chief Meteorologist Mark Nelsen