Long Range Outlook: First Wet & Cold Pattern In 2 Months?

February 16, 2015

We are now in our 7th week of upper-level ridging and/or split flow giving us warmer than normal weather.  In fact most of the past three months we’ve seen ridging over the West Coast or just a little bit to the east or west of us.  The only significant breakdown of the ridge was around Christmas when several cold and wet storms moved through the region.

It appears that this pattern will persist another 8-10 days, but all long-range models show a change in the last few days of February.  Models have been showing this for the past 4-5 days too.  To highlight:

  • Mild and dry weather continues for about one more week across the Pacific Northwest
  • Wetter and cooler weather arrives the last couple of days of February…plan to finish dry weather projects by that time.
  • Ski areas may see their best snow conditions since Christmas NEXT weekend (Feb 28/Mar 1).  But nothing will change for this coming weekend; lots of thin spots down low still.
  • It’s possible some closed ski areas could open up again by the first full weekend of March

Today was great, tomorrow looks the same, and then a mix of clouds and sun coming up the last few days of this week as the ridge breaks down a little.  Then the ridge pops back up quite strong to our west over the weekend.  Look at Sunday:

gfs_sunday

With the ridge slightly to our west, we get a cooler push of air out of southwest Canada Sunday and Monday.  Not an arctic blast by any means, but we likely won’t see 60 degree days.  More typical low-mid 50s instead with the gusty east wind.  I noticed both the GEM and ECMWF (12z runs) had a very strong pressure gradient on Sunday, but the 00z GFS does not.  The 00z GEM on the other hand has a significantly colder push of air, one that would give us high temps in the 40s with more of a winter feel Sunday/Monday.

Beyond that, the upper-level ridge then takes a few days to flatten, then redevelop much farther west.  Here’s the 00z GFS for Saturday the 28th, and the following Wednesday the 4th of March.  gfs_sat28

gfs_wed_4 Wow…quite a change from what we’ve seen in January and February!  This can be a great pattern for mountain snow, the GFS would give us snow levels 2,000-4,000′ through period.

Is there much confidence in this pattern change?  I think so…take a look at the 00z GFS, 00z GEM, and 12z ECMWF ensembles.  It’s 500mb height and anomaly:  gfs_mar3 gem_mar3 ecm_mar3

They are all in almost perfect agreement by Tuesday, March 3rd…two weeks from now.  At least the ensemble averages are…this leads to high confidence of a pattern change towards colder and somewhat wetter as we head into March.  The first significant rain and mountain snow arrives a week from Thursday, the 26th.

A huge question is whether it’s a temporary change…like back at Christmas.  Or is it the classic switch to wet/cool as meteorological spring arrives?  Good question.  The monthly run of the ECMWF from last night implies it’s going to last longer than a week.  Here is the map for week 3, March 1st-8th…pattern is the same.

500za_week3_bg_NA

Then week 4 which takes us into mid-March:

500za_week4_bg_NA

Still the same pattern with the upper level high out over the Aleutian islands.

Chief Meteorologist Mark Nelsen


Record Highs Today…Feels Like Spring!

February 16, 2015

What a string of warm days…4 out of the past 5 days we’ve seen temps above 60 in Portland.

Today the dry east wind pushed Salem up to 66 degrees, your warmest February day since 2005!  Here are the other records in the Willamette Valley:

MarkRecordHighTempsMetro

Tomorrow should be exactly the same as the east wind keeps the fog away.  There will be a dramatic change Wednesday though…a marine push in February!  It’ll be coupled with a weakening front dragging through in the afternoon.  The combo of the two means cloudy skies, maybe a sprinkle, and temps 10 degrees colder. Check out our RPM model showing the clouds surging up from the south and inland:

MarkRPM_Cloud_Snow_Fcst

MarkRPM_Cloud_Snow_Fcst2

MarkRPM_Cloud_Snow_Fcst3

Beyond that, no dramatic changes for the next 8-10 days.  The upper-level ridge pops up just to our west again late this weekend and early next week.  That means more east wind, although it’ll be cooler since we’ll have chilly Canadian air seeping south.  The GEM and ECMWF both show about a 20 millibar pressure difference from Spokane to North Bend Sunday afternoon as this cooler air arrives.  This could lead to a decent downslope wind event Sunday/Monday.  Either way, expect dry weather and sunny skies.

More on the long-term forecast later…the new ECMWF monthly maps are in and still show a big change in the pattern late next week…

Chief Meteorologist Mark Nelsen