Wednesday’s Storm: Very Low Confidence So Far

December 12, 2016

9:30pm Monday…

Forecasting specific totals for Wednesday’s event would be a very risky endeavor this evening.  This is the one time I think we don’t have a good idea what’s going to happen over the metro area just 48 hours ahead of time.  We need to give it more time and several more model runs to see if they come together and tighten up their forecasts.  This is quite similar to what happened in early February 2014.  Just two days ago it appeared that Wednesday’s system would be totally missing us to the south.   Then in the past two days models have trended north and wetter over us.  But again this evening there has been a southward trend again; several show LITTLE OR NO PRECIPITATION OVER US WEDNESDAY!  Take a look at this compilation of the evening runs.

marksnow_pdx_models

I made a rough conversion of rain to snow, assuming a 1 to 10 ratio.  On average 1″ of rain can give you 10″ of snow.  Wetter snow a bit less, drier snow more for each inch of rain.  Do you see why it would be nuts to forecast a snow total right now?  You can see the closest approach of the precipitation at 4pm Wednesday on our RPM model:

rpm_cloud_snow

I do have high confidence with three points

  1. Central Oregon and the Central/Southern Oregon Cascades are going to get hammered!  That .87″ at Bend could give them 8-10″ snow since cold northerly flow will be pushing south into that part of the state.
  2. IF we get precipitation (likely in the form of snow) then it would arrive Wednesday afternoon at some point.
  3. Wednesday will likely be a dry day in most of Western Washington.

Stay tuned, I GUARANTEE there will be more twists and turns the next 24 hours!

Chief Meteorologist Mark Nelsen

 


Another Busy Weather Week!

December 12, 2016

11:45am Monday…

This will be very short; I’ll have time later today for a more in-depth posting.

I’m real busy the first part of today:  Fixing a faucet, a weather school visit, & a meeting.  Then I need to figure out the forecast for the later shows.  Here are a few things I notice right away:

  1. Cold east wind returns Tuesday, but it’ll be dry and reasonably comfortable…highs around 40.
  2. We probably have some sort of snow/ice event coming later Wednesday & Wednesday night as a very wet system will move directly across Oregon from west to east, mainly across the southern portion of the state.
  3. As of now, it could be a BIG deal, or it might be only flurries because models haven’t decided on the exact track and how much moisture makes it this far north
  4. Parts of our viewing area could even be dry!  Check out this mornings WRF-GFS 24 hour precipitation forecast ending 4am Thursday, when the “event” is over:

or_pcp24-72-0000

This is only ONE run of ONE model so this is only one possibility.  In this case Astoria and Kelso would see nothing…a dry afternoon/evening, Portland gets maybe an inch of mainly snow,  and Redmond/Bend get hammered with a major snowstorm.  The more trusty ECMWF is juicier, showing between 1/2 and 1″ of precipitation!  That would obviously be a big deal.

I’m very confident we’ll see something different on the next 3 main model runs (each 12 hours).  This event is still 48+ hours away.

So you should be thinking and preparing for the possibility that SOMETHING frozen may fall Wednesday afternoon/night.  Otherwise just chilly and dry until that time and AFTER that time too (Thursday-Saturday).

Gotta go…I’ve kids to educate and meetings to attend…but at least the kitchen faucet is working.

Chief Meteorologist Mark Nelsen