9pm Update…Not Much Has Changed

All the evening models except the ECMWF are in and I don’t see anything to change my mind about tomorrow.  The main change was two models being a little drier and kept the heavier stuff to our south.  That could mean the Gorge gets less than our current forecast.  We’ll see what the ECMWF shows around 10:15pm.  These graphics summarize what I’m saying on the evening newscasts:

  Here’s another version of the same thing:

The National Weather Service has a Winter Storm Watch out for most areas west of the Cascades, although that’ll probably become a warning soon.  The Gorge is where the main action is going to be though!

Why am I still not going for big snow?  Most models still show a wedge of above freezing air around 3,000-5,000′ tomorrow morning.  That would argue for more ice pellets or freezing rain, cutting way down on snow totals.

Keep in mind if models are running just a few degrees too warm up above we have a snowstorm on the way tomorrow!  Luckily everyone starts at home tomorrow morning so it’s not like half the population will be trapped at work at 3pm when snow/ice hits.  It you wake up at 7am and it’s snowing like crazy…stay home!

I’ll be getting up early tomorrow to see how things are going

Chief Meteorologist Mark Nelsen

Snow/Ice Thursday? Noon Update

Is there going to be a snow/ice storm in Portland tomorrow?  I’m not sold on that for now, but you should make (worst case) plans for tomorrow morning’s commute.  We’re only talking a few degrees between wet roads and icy roads!

A few minor changes in models/maps have made the forecast even more challenging now for the Portland Metro Area.  It would be a poor choice to forecast all rain tomorrow in our area.  Last night I pointed out that was a possibility we’d see spots of freezing rain and/or spots of snow (far westside) and now the chance of SOMETHING frozen has increased in both cases.  That said, I’ve never seen a major snow/ice event in an airmass that sees high temperatures around 40 degrees (today).  Salem in the mid-upper 40s this afternoon?  That doesn’t inspire a lot of confidence in a snowy/icy day tomorrow either.  But here we go…

The National Weather Service is going all-out for a MAJOR event tomorrow.  A winter storm watch for much of northwest Oregon, a blizzard watch for the Gorge, and a winter storm watch there as well.  You can see the area in the blue/green, they have it all the way down to Salem.  They are thinking 4-6″ snow for us, that IS the official forecast!  And 1-3″ snow plus possible freezing rain in Salem.

This is my forecast as of early this afternoon.  We get another run of models in between 7-9pm tonight, so that will be the “final call” and my forecast may change!

METRO AREA

• A SNOW STORM IS DEFINITELY NOT ANY SORT OF A “LOCK” AT THIS POINT. Don’t get mad at me if at noon tomorrow it’s raining with some icicles hanging off a few trees and a wet dusting of snow on the ground.
• Light snow/freezing rain/rain (a wintry mix) arrives around daybreak tomorrow and continues throughout the day.
• Temperatures dip to right around freezing or even a notch below around sunrise, then rise into mid 30s by noon
• 1-2″ snow is possible, but more likely a sleet/snow/freezing rain mix.
• 3-5″ snow is possible in western Washington/Yamhill counties (Carlton, Forest Grove, Banks, 2-4″ Scappoose)

IF temperatures only dip to 32 (most likely scenario), many roads may stay wet, especially if we get freezing rain only.   You need temperatures around 30 or lower to freeze icy onto roadways during the day. Snow will more easily stick to roads, so if I’m a couple of degrees off and it’s all snow?  It’ll be a real mess! 

Iciest roads are likely to be in West Hills and near the Gorge if it ends up being a minor marginal event.

WILLAMETTE VALLEY

• Probably too warm for either snow or freezing rain (except for a pocket or two)
• Up against the Coast Range (western side of valley) a better chance for a couple inches of snow…maybe Sheridan area?

COLUMBIA RIVER GORGE

• Looks like a winter storm!
• Mainly snow all day tomorrow
• 5-8″ totals
• Mainly freezing rain or ice pellets around Corbett, Cape Horn…could be thick glazing by late in day
• Snow ends Friday morning and it stays cold through the weekend, much of the snow is going to stick around
• I-84 will be a real mess, might want to put off travel for 1-2 days

CASCADES

• It’s going to snow on Mt. Hood
• 8-12″ by Friday morning

So why did I change my forecast towards colder/icier?

1. Soundings on WRF-GFS and NAM-MM5 are SLIGHTLY colder

2. Once WINTER STORM WATCH and BLIZZARD WATCH show up on people’s phones/email I can’t ignore it in a situation like this that is a close call.

3.  ECMWF (my favored model) still shoves a ton of moisture in over us, hard to ignore that

What points toward no big snow event?

1.  Surface temps are marginal (as mentioned above) ..even with evaporational cooling it’s going to be tough to get us below 32 tomorrow morning.  If model soundings are correct and it’s only ice pellets or freezing rain, most streets will remain wet  Our big snow/ice storms happen in an airmass where the high temp is 35 or lower (under sun) the day before.  There isn’t any colder air coming…this is it.

2.  Worried about all models (except ECMWF) shoving moisture farther south now.  12z NAM says we are on the northern edge of the precipitation…Hmmm

3. Still don’t like those soundings.  The WRF-GFS has done quite well in the past with soundings predicting precipitation type.

4.  This isn’t a biggie, but our RPM is saying all rain with just freezing rain spots.  We’ll see, not always a stellar performer in the past.

I’ll try to blog again after the 00z models come out.

Chief Meteorologist Mark Nelsen