Flood Watch Through Wednesday

December 6, 2015

10pm Sunday…

Most of the FOX12 viewing area over and west of the Cascades is under a Flood Watch (from the NWS) through Wednesday.  It’s pretty straightforward…too much rain is coming in the next 3 days!

I’m at home this evening and not real sure if I’ll make it to work tomorrow.  I can barely talk with some annoying form of a cold & laryngitis.  Hopefully I’ll feel better tomorrow and, more important, sound like a normal human being on-air.

But it doesn’t keep me from posting weather info and charts/maps!

We are in a classic wintertime strong westerly jet stream regime.  We haven’t seen much of this in the past two winters.  But it’s here for another 5 days or so.  Here’s the 250mb jet stream windspeed map for 4pm today:

gfs_jet_250_npac_2

Note the speeds over 200 mph in the central/western Pacific.  It’s pretty much a straight shot from Japan to Oregon the next few days.

So we’ll see one system after another racing eastward with plenty of moisture and areas of low pressure to produce wind tracking along with them.

Between right now and early Wednesday morning, we’re under the influence of a very warm airmass…snow levels jump to 7,000′ or so through daybreak Wednesday.  As a result, keep in mind that all precipitation will fall as rain at ski resorts and mountain passes through that time.

The biggest surge of rain appears to be tonight, tomorrow midday/afternoon, and again Tuesday evening through daybreak Wednesday.  There will be a break for most of us during the day on Tuesday.  That said, models are painting a very wet 72 hour rain total picture for us.

I would estimate we’ll see at least 3-4″ in the “driest” parts of the northern Willamette Valley the next 3 days.

The Oregon and Washington Cascades along with the highest parts of the coast range will receive the brunt of the rain and strong westerly wind runs into the north/south oriented ranges.  Expect 6-14″ on the west slopes of the Cascades and Coast Ranges.  Here are 4 different model forecasts of 3 day rain, this evening’s run of the GFS, ECMWF, & WRF-GFS (UW):

These forecast totals are similar to the big event that started the wet season with a bang back in late October, back then soils were very dry from summer.  This time soils are already wet and there is snow on the ground up above 4,000′ too.  A bunch of that snow is going to melt since a 1 or 2 foot deep snowpack can’t absorb 8″ or more of water dumped on it.  As a result I would expect some river flooding in our area.  Of course if we get too much rain in a real short amount of time that’s when we get the localized urban flooding too.

For the skiers…is it time to panic?  Definitely not.  As mentioned in previous posts, all signs point to a cooldown with COLDER systems after Wednesday.  I have a feeling we will see FEET of snow before we get to Sunday the 13th.  Check out the 3 day total from the WRF-GFS ending Friday morning…maybe 8-12″ on Mt. Hood.

or_snow72.108.0000

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Then 3 days later…2 feet or more additional!

or_snow72.180.0000

The ECMWF model also has a good 2-3 feet of snow on Mt. Hood Thursday through next Tuesday (not shown).  This could set us up nicely for Christmas Break…Ski Season begins AFTER the warm rain this week.

Chief Meteorologist Mark Nelsen