A Warm Easter Weekend?

April 2, 2012

That’s the challenge in the forecast today…will we see our first stretch of nice weather here starting this weekend?  Maybe not…more on that in a moment.

For the short-term, today was a classic nice spring day: easterly wind through the Gorge, light south wind developing up the Valley, more sun than clouds, and an approaching wet cold front.  Funny that it seems so warm yet only up to just a few notches above the 60 degree average for April 2nd.  Of course that’s because we’ve only seen 3 other days in the past month into the 60s.

Forget the 60s for awhile because the cold front that brings rain tonight is also associated with a large and cold upper level trough that’s going to sit over the West Coast tomorrow through Friday.  One significant difference with this trough compared to the past few weeks is that we don’t have all that much rain coming and it’ll be mainly in the form of showers.  Wednesday, Thursday, and maybe Friday afternoons will feature the classic showers, sunbreaks, hail, and maybe scattered thunderstorms pattern.  The strong April sun heats the earths surface each day and the air bubbles up quickly into the colder airmass above.  We should see some of those towering cumulonimbus clouds at least Wednesday and Thursday afternoons.

Beyond that is quite a challenge.  The 00z ECMWF and 12z GFS both showed ridging building strongly into the Pacific Northwest for Easter Weekend and early next week as an upper level trough digs offshore.  I almost bit off on that.  The 12z GFS with it’s +10 or +11 850mb temps plus easterly flow next Monday could put us into the mid 70s.  But then the 12z GEM and ECMWF came in with much cooler temps.  What’s going on?  Take a look at the 500mb ensemble anomaly from the 12z GEM, GFS, and ECMWF:

On Monday afternoon, the GFS has highest upper level heights much closer to us and the ECMWF has it centered over the Rockies.  This explains the warm temps on the GFS, and also shows brushes with precipitation and cooler temps for us based on the ECMWF.  For that reason we kept temps in the 60s, but still above average Sunday through Tuesday.   

So even though Saturday through the middle of next week brings pretty decent early April weather, I don’t see the beginning of a unusally warm spell at this point.  As of now, we can probably squeeze out a dry and warm Easter Sunday with temps above average though!

Here are the 12z ECMWF and 12z GFS 850mb charts:

On the ECMWF you can see that it’s just around average (green line) for the next 10+ days, chilly of course for the first 4-5 days, then warmer after that. 

The GFS is, well, a little extreme.  Note the blue line (operational run) is the warmest from Sunday PM to Wednesday PM next week.  But even this run is about “average” over the next two weeks or so going from cool to warm to normal or cool again.

By the way, since I left on the last day it snowed in Portland and haven’t blogged about it, here are the final numbers for Portland snow this winter:

Winter Total: 3.1″

November = 0.0″  
December = 0.0″  
January = 2.3″  
February = Trace  
March = 0.8″  

…and the actual days snow was measurable in the city:

Jan 17:   1.3″ (just before midnight)
Jan 18:   1.0″ (after midnight, same event)
Mar 1:    0.3″
Mar 21:  0.1″ (just before midnight)
Mar 22:  0.4″ (after midnight, same event)

That March 22nd snow is the latest measurable in the city, at least through PDX’s history (1940).  Many of us are aware (and now you are) that the downtown Portland observation site has seen snow the first week of April 1933 & 1935…several inches during the latter!  The latest measurable was 0.1″ recorded at that site on April 14th, 1926 as well.  That may have been a hail observation…maybe not.

Chief Meteorologist Mark Nelsen