Flooding Rains For Some of Us Friday

1pm Thursday…

Plenty of rain is moving through the region this morning…radar image is lit up like a Christmas tree

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For many days weather forecast models have been forecasting an “atmospheric river” to develop across the eastern Pacific, sending tropical moisture northward into the Pacific Northwest.  Models have been in excellent agreement showing this basic setup and that heaviest rain would occur from late today through early Saturday.  But an atmospheric river is a narrow corridor; like a hose in the atmosphere.  It also tends to move north/south throughout an event as weather disturbances ripple northward.  So forecasting exactly which part of the region gets nailed by heavy rain is tough. But finally this morning models are good agreement.  The heaviest rainfall the next 36 hours will be between Pacific City and Hoquiam along the coastline (centered around Astoria), and into Southwest Washington (Woodland/Kalama to Olympia).

The Highlights

  • Rain continues at times through this evening in the Portland metro area and most areas west of the Cascades
  • After sunset and through the night, a band of heavy rain develops from around Astoria to Chehalis.  That heavy rain may extend as far south as Forest Grove, Scappoose, & Woodland.
  • Most of the metro area will NOT see heavy rain tonight or Friday morning
  • South of Portland, rain will be very light or even dry at times through Friday evening!
  • A warm southwest wind (a Chinook!) this evening through Friday morning brings gusts 30-40 mph in the valley and temperatures into the 50s
  • Cascade snow changes to light rain at times tonight and Friday at all ski resorts.  Avoid Friday skiing, although it may briefly dry out at times up there.
  • Steadier rain resumes in metro area Friday afternoon/night, but it’s unlikely we see any sort of widespread flooding from Portland south.

Local flooding is possible anywhere north & west of Portland tonight and Friday.   The NWS has a flood watch in effect which means flooding is possible.  This could be an event similar to February 12th when several inches fell in Banks, Vernonia, Scappoose, Kalama etc… but very light rain central/south/east metro.

For the weather geeks…

It was good to see models come together the past 24 hours.   I love this graphic; the integrated water vapor transport or IVT.  Shows where the “river” is aimed this evening at 7pm, 10pm, and again Friday at 10pm.

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The ECWMF is probably farthest north showing the intense rain band developing this evening to our north; hitting Centralia/Chehalis and Olympia with the biggest downpours.  Six hour rain ending at 10pm

ecmwf_6hr ending 10pm

Then 6 hours later ending at 4am Friday

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and 10am-4pm Friday

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The 24 hour total ending Friday afternoon shows very little rain south of Portland, just an inch in the city, but a solid 3-5″ up north

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GFS model is similar this morning although an even more stark cutoff to rain in metro area.  It pours in Forest Grove but sprinkles in Molalla

gfs_24hrfridaypm

And finally the GEM (Canadian)

canadian_24hrfridaypm

Of course if models are 50 miles off on placement, heavy rain could still show up in the metro area.  Good reason to keep the Flood Watch going!

What about Mt. Hood?  Is the meager snow pack going to wash away?  No, although we sure won’t gain much.  It’s very early in the season, but snow pack is running at less than 50% of average in much of northern Oregon

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Warmer air is surging into the Cascades right now and will push the snow level above 6,000′.  The bad news is that with the fire hose aimed north of Mt. Hood, snow levels stay high until early Saturday.  Anything that falls from this afternoon through Friday evening should be in the form of rain, not snow.  The good news?  The main band of rain is so far north that I don’t expect a dumping rain on Mt. Hood Friday, just light rain at times.  That said, a warm/humid airmass eats snow more quickly than any sunny 40 degree day in December.

Then as the whole system slides south and east Friday night, snow levels drop and we should see at least 6″ on the back side of this system.  Very tough to get additional terrain and/or ski areas open for Christmas Vacation without a good dumping.

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That’s it for now.  I’ll be at work all afternoon/evening.  We have lots of newscasts, you can catch us at 4, 5, 6, 8, 9, 10, or 11.

Chief Meteorologist Mark Nelsen

18 Responses to Flooding Rains For Some of Us Friday

  1. Anonymous says:

    I personally love these type of weather events. When you only have a weather event that’s tens of miles wide for the worst of the impact zone. Even when it’s a close miss, is still exciting. This reminds me of the close snowmageddon on superbowl Sunday a few years ago.

  2. W7ENK says:

    The wind is really howling out there tonight. The stand of 100’+ Dougies to my South are just screaming right now! 😱

  3. Joshua Lake Oswego says:

    The 00z NAM-WRF is comical. 38”!!! for a portion of the north Oregon coast and south Washington coast through Sunday morning. Essentially the whole I-5 corridor in Washington gets hammered. Portland metro gets around .50”. Bustaroo! Watching the radar will be an excruciatingly frustrating experience.

    • Mr Realist says:

      Oh the butthurt on here is hilarious, get real folks. Things happen and don’t happen. Just think, fake cold is only 10 days out. Are you guy’s going to whine and cry when that doesn’t happen. We are having a true PNW winter, enjoy it and stop blaming forecasters for your lack of excitement!!

    • W7ENK says:

      Then don’t watch the radar. Maybe go do something else, rather than torture yourself like that?

  4. runrain says:

    Gettin’ pretty windy out there. And warm!

  5. We’re expecting 6 plus inches in the next four hours.

  6. rmlounsbury says:

    I am highly entertained by the the news channels saying that you can’t trust your weather app because it has no human interpretation.

    Followed by human forecasters predicting apocalyptic rain fall totals from an AR event only to have it scoot north leaving us with your standard PNW all-day-rain.

  7. rmlounsbury says:

    I am highly entertained by the the news channels saying that you can’t trust your weather app because it has no human interpretation.

    Followed by human forecasters predicting apocalyptic rain fall totals from an AR event only to have it scoot north leaving us with your standard PNW all-day-rain.

    • Tanis Leach says:

      In all fairness most of them did say up to x inches was a possibility. X is a different number for each meteorologist. I wouldn’t call that an exact prediction.

  8. WEATHERDAN says:

    After this non event it looks to get quit cool. Almost enough to call it cold. In fact I expect to see the snow level down to 1k feet at times between the 23rd and January 4th. Mainly dry but with a light rain shower or snow flurry or two here and there. At the very least more Christmas like than this week. Peace and Merry Christmas.

  9. Joshua Lake Oswego says:

    Thanks, Mark. I await your apology, W7. I have been looking at every common weather model and then some at least 10 times a day since this event first showed signs of happening. In fact, I talked about the threat of flooding possibilities late this week before any local weatherperson that I am aware of. Rain is my thing.

    So… when I said that most of us will be too far south and east of the hose for big-time precipitation, I knew what I was talking about (as much as possible with weather forecasting). I know there are variables involved and things can change, but trending and near-100% model agreement gives a relatively high degree of certainty.

    • W7ENK says:

      lol

      Ehhhh, no. You’ll get your apology after Sunday, but only if it’s warranted.

      Meanwhile, I’m closing out the day with 0.74″ of rain. That gives me a 2 day total of 0.84″ with two more days to go before this event is over.

      If we hit 3 inches by Sunday night, you bust.

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