WrfSnow

It was another chilly night with most of us well down into the 20s.  But this morning clear skies are allowing GOES-17 (will become GOES-WEST this week) to see exactly where snow fell yesterday.  It’s just about all east of downtown Portland; I drew in the red line and dotted line is West Hills

Sat

We have just about lost the cold easterly wind coming through the Gorge and it goes away by midday.  Then a very gusty southerly wind arrives late this afternoon and continues through about 10pm or so.  What does that mean in your life?  In the next 12 hours we transition from a “continental airmass” (cold & dry) to our normal “marine airmass” (mild and wet).  Even though the snow is a lot of work for me professionally, I hate to give up the beautiful thick snow cover and blue skies we’re seeing this morning.  When you wake up tomorrow morning, all our snow west of the Cascades (and west of Bonneville Dam in the Gorge), will be a soaked and heavy mess under gray skies and a steady 40+ degree rain…

Sometimes we get an ice storm or snow storm during this transition back to milder weather, but that’s definitely not the case this evening and overnight.  Here’s what I expect for the next 48 hours west of the Cascades and the western Gorge from around Multnomah Falls westward.

NOW THROUGH MONDAY A.M. COMMUTE

  • We’ll be sunny through midday, then clouds arrive in the afternoon.  Right around sunset showers show up, likely mixed with snow at first, especially from the metro area north.
  • We’ll quickly transition to all rain west of the Cascades during the evening as the sticking snow level rises to around 2,000′ during the night from the metro area south and around 1,000′ up in Clark and Cowlitz counties.
  • No sticking snow in any of the lowland cities from Longview down to Eugene.  Temperatures rise to around 40 degrees during the night

MORNING MORNING COMMUTE WILL BE RAINY WITH TEMPS AROUND 40 DEGREES

A strong southerly wind picks up from 4-10pm as well.  Expect gusts 25-35 mph, maybe even a gust to 40 mph somewhere during this time.  Wind backs off after midnight

MONDAY

A very rainy day!  We’ll get at least an inch of rain and temperatures rise into the mid 40s.

MONDAY NIGHT & TUESDAY

Rain continues, may be heavy at times, then it backs off to showers Tuesday.  By Tuesday morning there could be sticking snow down to around 1,500′ again, but that’s not in the metro area.


WHY AM I SO CONFIDENT ABOUT RAIN ONLY TONIGHT?

Because atmosphere warms today/tonight with that gusty southerly wind, and in 27 years forecasting here I’ve never seen snow in this setup.  Note the relatively deep low pressure passing by just to the north at 10pm.  Also interesting; as it moves by it’s trying to develop a west wind in the Gorge, a sure sign those areas west of Bonneville will struggle to maintain sticking snow instead of rain

slp.18.0000

And the WRF-GFS snow forecast is pretty clear…

wrf_snowthruMonday4am

WHAT ABOUT THE CENTRAL/EASTERN GORGE?

I still expect a big dumping of snow tonight through Tuesday from Cascade Locks to The Dalles.  It may become a very wet snow later tonight if there’s any sort of west wind push.  But in the next two days you should see 12″ to 20″, most likely the 20″ would be above river level.  Part of that cold airmass east of the Cascades (and eastern Gorge) is going to get wiped out by tonight’s system.  Here’s the total snow forecast by Tuesday morning.  Ignore the blips over the metro area.  This model tends to over-do cold showers-type snowfall (Tuesday) down around 1,500′ and below.

wrf_snowthruTuesday7am

THE RAIN

This morning’s Euro is the 2nd one to show a stationary front over us from Monday through Tuesday afternoon.  It’s going to be a HUGE soaking for Northwest Oregon and Southwest Washington.  It gives some areas 3″ of rain during that time, luckily snow levels only rise up to 3,000′, so I don’t anticipate any big river flooding.  That said, I’m sure creeks will be rising rapidly

ecmwf_precipthroughTuesdayPM

WRF-GFS agrees, although not quite as heavy; everyone west of the Cascades getting around 1.5″ or more

or_pcp72.84.0000

Chief Meteorologist Mark Nelsen

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