Brief Rain This Week, Then Back to Dry

February 4, 2013

A weak cold front is sitting offshore this evening; that plus a second wetter and stronger front give us rain off/on through Thursday.  This appears to be another short & wet break in our prolonged drier and calmer than normal pattern that has persisted since Christmas.  The 00z GFS only has about 1/2″ rainfall the next 3 days, our RPM

RPM_RAIN_NWOREGON

has closer to 1″.  Either way, not a hugely wet set of days ahead, just, you know…the usual.

Beyond Thursday…BORING!  This has been a very slow winter with just a few interesting weather events here and there, mainly before Christmas.  I don’t see anything exciting for the next 10 days either.  That will take us to Valentine’s Day (a week from Thursday). 

Why so dead?  We keep seeing a similar pattern of upper-level ridging developing near or just off the West Coast.  When it was right over us in mid January we saw a strong inversion with cold air in the valleys and warm air in the mountains.  Well now we are heading towards the 2nd week of February.  Inversions can definitely still set up this time of year, but the increasing sun angle means more energy reaching the earth’s surface compared to a month ago.  The result is that the same freezing level (for example 8,000′) in February will produce warmer temps down here at sea level compared to last month.  It’s easier to get into the 50s as we head into mid-February.   Often in mid-late February we get some sort of “false spring” weather with high temps up around 60 or even above.  Right now I don’t see that between now and Valentine’s Day.  But we probably have more weather like Saturday’s on the way for this weekend and early next week.

Looking farther ahead…

Interesting maps at times the last 2 days with some models and some runs of those models indicating that somewhere beyond Valentine’s Day we’ll see the upper ridge back farther offshore and let colder air come down from the north.  The 12z ECMWF, GEM, and GFS all showed this on their ensembles around Day 12-16 (beyond today).  Now the GFS has backed off, in fact the 00z GFS keeps ridging over us throughout the entire 16 day period after Thursday!  It’s a bit of an outlier showing no rainfall for the following two weeks.  The GEM this evening has flatter ridging, but still no cold air nearby around the 14th (the farthest I get maps out so far).  Here is the 00z GFS ensemble chart, still showing some pretty decent spread in solutions, but generally signficantly warmer than the 12z run:

tseries_850t_000-384_Portland

The 12z ECMWF ensemble is here, notice quite a few very cold members beyond the 14th:
tseries_850t_000-360_Portland

So as of now, we can rule out any big cold spell, low elevation snow, or stormy weather before Valentine’s Day.  Beyond that is still very much up in the air.  We may be finished with any big snow/cold chances, or we may have the best of winter still awaiting us in the last two weeks of the month; it’s just too early to know.

Chief Meteorologist Mark Nelsen


Monthly ECMWF Maps

February 4, 2013

This is for the hardcore folks only, the Sunday night 30 day run of the ECWMF model.  Each map represents the one week average of 500mb heights.  Ridging is shown by positive anomalies and troughing by negative.

500za_week1_bg_NA
500za_week2_bg_NA

500za_week3_bg_NA

500za_week4_bg_NA


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