7 Day Forecast: Winter to Spring to Winter…Then Repeat

March 6, 2012

Clear skies along with very dry air over us means no morning fog but a nice hard freeze.  We haven’t been below 29 degrees in March here in Portland since 2002.  We MIGHT do it tonight.  For sure the outlying areas will be well down into the 20s with light wind.  Still, this is no mid winter arctic blast, just a chilly late winter or early spring night.

Tomorrow we have a nice day with temps a bit warmer than today; sunshine from sunrise to sunset.

Thursday is THE DAY YOU NEED TO GET SICK.  All signs point to a perfect spring “east wind day”.  Look at the surface map for Thursday morning: 

About 4-5 millibars easterly gradient through the Gorge in the morning with high pressure east of the mountains goes almost flat by sunset, so we get the downslope warming through most of the day, then the wind dies down as the strong March sunshine warms us up late afternoon.  850mb temps somewhere between +7 to +9 could push us as high as 65 in parts of the metro area.  We’re going 62 at PDX.  Either way, our first real springlike day.  And you really need to savor it because we go back into wet weather this weekend and most of next week.  In fact all models pushing Friday’s front inland midday at the latest, so we’ve gone from a 64 forecast for Friday to around 50.  Figured I should jump on that quickly to avoid too much disappointment.

Speaking of next week, a cold upper-level trough develops again nearby, but this one will be different.  It digs down to our west, in the eastern Pacific, and sends waves of rain and mountain snow our way.  The last few have swept right through us in northwest flow with a ridge well offshore.  West or southwest flow is much milder than those systems that come in from the northwest.  That said, one pocket of cold air rotates around the low and moves through the Pacific Northwest Sunday night and early Monday.  The GFS says cold enough for snow in the hills again, ECMWF (at least so far) is a bit warmer.  It is an unusual pattern to get low snow levels with a deep low way offshore.  Beyond that, the 00z GFS shows a deep surface low tracking offshore Monday, up towards Vancouver Island.  This would give us a chilly, wet, and stormy March day on the Coast, and real wet inland too.  Here is the WRF-GFS for Monday afternoon:

More wet weather through much of next week…check out the 00z GFS ensemble chart, then the 12z ECMWF chart:

 And for comparison, you see the unusually warm winter temps turning into warmer than average spring temps in Chicago’s chart:

Chief Meteorologist Mark Nelsen