11pm: Looks Snowier For Metro Area

February 5, 2014

I think there is a good chance now that widespread snow will fall in the metro area tomorrow afternoon.  If so, it could be a mess since it’ll be dry in the morning and most schools/businesses will be in session.  We sure don’t need an Atlanta repeat in Portland tomorrow evening, so please think carefully before you head out in the morning.

The big story this evening is that models have shifted farther north with the precipitation and the evening ECMWF model (what I was really waiting for) still runs a ton of moisture with a surface low directly into northwest Oregon.  That gives me enough confidence to say we’ll have our first widespread snow event in the metro area since December 2008.  Here’s what I used at 10pm:

MarkSnow_PortlandOutlookPercentages

 

MarkSnow_PortlandOutlookPercentages

Here is our latest RPM model snow forecast:

RPM_SNOWACCUM

 

I don’t have graphics showing how much the ECMWF model gives us snowfall-wise, but it appears to be enough for 3-5″ possibly.

Chief Meteorologist Mark Nelsen


Winter Storm Watch: Western Lowlands of Oregon Thursday

February 5, 2014

The NWS has put up a winter storm watch for most of northwest Oregon.  Remember a watch means something COULD happen and we’re WATCHing it closely.  You can read my posting below for a bit more detail.  Here is our forecast (as of 5:30pm)

MarkSnow_PortlandOutlookPercentages

This is enough of a risk that if you have a choice to drive a “snow car” or “non-snow car”, take the one that can handle snow for Thursday.  For sure do it from Salem south.  But even here in Portland.  There is an unusually high level of forecast uncertainty on snow amounts here in the metro area tomorrow, so I assigned these percentages to several “events”:

MarkSnow_PortlandOutlookPercentages2

There is a very good chance this forecast will change as new models come in between 8pm and 10:30pm.  If those models come in much wetter like this morning’s ECMWF, my snow forecast is going way up for the metro area.

Stay tuned!

Chief Meteorologist Mark Nelsen


Snow Possible in Valley Thursday & Friday

February 5, 2014

The National Weather Service has issued a Winter Storm Watch for the south Willamette Valley for Thursday, that includes Albany/Corvallis down to Eugene.  In the valleys, a winter storm watch is issued when 4″ of snow is possible.

The Highlights

1. We have a greater than normal level of uncertainty with the forecast for the next 3 days.  Models are in quite a bit of disagreement about how much snow falls where and when.

2. Whatever falls in the valley from Kelso to Portland to Eugene through Saturday should be frozen (snow or freezing rain).

3.  You should be flexible with work and other plans Thursday, Friday and Saturday.  And assume the forecast could change with just 24 hours notice.

4. A very good chance areas south of the Portland metro area get a decent snowstorm in the next 2 days.

I mentioned this in last night’s posting, but now it’s even worse.  A wide variety of model solutions for the next 2-3 days.  ALL models show some surface low pressure systems tracking along the arctic air boundary draped across the middle of Oregon.  ALL bring moisture at least through southern Oregon.  But SOME bring it much farther north, right into the Portland metro area and even Longview/Kelso.

Here is our RPM model forecast (it isn’t always right on!) for noon tomorrow.  Light snow that starts in the southern valley slips north and starts showing up tomorrow afternoon in the metro area.

rpm_noon_thu

and then at 4pm tomorrow showing the heavier snow down the valley.

rpm_4pm_thu

and the total snowfall forecast by Friday morning.  The 2″ line cuts across the south side of the Portland metro area with 4-8″ south of Salem!

rpm_snow_4amfri

But look at the snow accumulation forecast from UW’s reliable WRF-GFS model:

or_snow48.48.0000

much farther south!  In this case there would be NO snow in the valley tomorrow, but a nice snowstorm at Roseburg.  Now these are only two models, we have more, but I wanted to illustrate what a tough forecast it is for tomorrow.  I should also point out both were “initialized” at the same time, early this morning.  Just 1/2 hour ago another very trusty model came in, the ECMWF (the European model).  It has decided to run the surface low pressure directly into the north valley instead, plunging the metro area and valley into a midday/afternoon snowstorm with gusty east wind and temps in the 20s!  Here is the 4pm precipitation forecast (with surface pressure lines too):

ecm_4pm_thu

This could produce 2-4″ in time for the afternoon commute…hmmm.

Luckily we have a few more models that come out this afternoon, then a whole bunch more this evening.  Hopefully they will come into better agreement.  We don’t need an “Atlanta-Style” commute  Thursday afternoon.

The main message:  There is a very good chance for at least some snow in the central/southern valley (and central coast) tomorrow, and it MAY spread farther north into the metro area, but we’re not sure yet.

Chief Meteorologist Mark Nelsen