11:30am Monday…

Are we going to wake up to a flood Tuesday? And have a bunch of snow at the same time? What? Whew…weather fatigue! Here’s the scoop

WHAT’S HAPPENING

A very wet stationary front sits over us tonight and early Tuesday, then moves to our south. It’s gonna pour between this evening and Tuesday morning’s commute, maybe up to 2″ of rain in 12 hours or so! That’s the major weather story for the next 24 hours.

  • We’ll see localized flooding of creeks, low areas, basements, etc… for Tuesday morning’s commute. Could be messy!
  • Then tomorrow’s rain will be more off/on
  • At the tail end of the system late tonight, temperatures MAY cool just enough that heavy rain changes to heavy/wet snow for a few hours in some part of the metro area. There’s a relatively low chance of this happening (see models below), but obviously a big deal if it happens in your area.
  • The NWS has issued a Winter Storm Watch for that possibility. It’s a WATCH which means it’s just a possibility. At this point this doesn’t appear to be a metro-wide snow event.
  • After evening models come in (around 8pm or so) we should have a much better idea if there’s going to be any brief changeover to snow.

TECHNICAL TALK

All models agree that we’re getting a huge soaking tonight. Check out the 24 rainfall from this afternoon to Tuesday PM on the WRF. 1.5 to 2.5″ in the metro area all the way down to Eugene!

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So that’s the easy part of the forecast. Snow levels climb up to around 3,500′ this afternoon and tonight; no chance for snow through midnight except in the central/eastern Gorge.

Of course the big question is whether we get an “isothermal atmosphere” on the back side of the front. That means precipitation is so heavy that the column of air overhead cools right down to freezing from 3,000′ or more on down It allows those huge snowflakes to make it all the way down to sea-level, or at least to your home. All morning models are in and only the WRF and HRRR models are showing that happening in any sort of widespread fashion. ECMWF says it may happen in western Washington county (Hillsboro westward to Coast Range). Other than that, ECMWF, GEM, GFS all say forget about it. All three models here

I have seen this happen in the past, Halloween 1993 and November 2003. Both those times it was the east/southeast metro area, spots like Gresham, Corbett, Sandy, Damascus, Estacada and south as the back edge of steady/heavy precip moved through. IF it happens, I think that would be the most likely area as the WRF-GFS shows, although it shows temps cold enough for hills in the entire metro area to get in on the action

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To wrap it up, there’s no reason to suspect we’ll have a white, snowy, hellish AM commute tomorrow. But there’s good reason to think we’ll have a watery, messy, AM commute. And keep a very close eye on this blog and FOX12 through the evening and morning hours tomorrow. I’ll be on TV much of the time between 5:00-11:30pm tonight. I’ve got you covered!

BTW, this entire time a huge snowstorm continues in the Cascades and to a lesser extent the central/eastern Gorge. Possibly up to a foot of extra snow east of Bonneville Dam in the Gorge. It appears 20″ have fallen since midday yesterday on Mt. Hood! More “feet to go” up there. Please be careful and ski with a friend, stay away from tree wells which can be dangerous during these massive snow storms.

Chief meteorologist

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