Spots of Ice Metro Area Wednesday AM

December 26, 2017

9:30pm Tuesday…

OVERNIGHT

This cold episode has just about played itself out in the metro area.  The cold air layer is quite thin, so I’m thinking it’s going to be tough to get precipitation in the form of snow as all models show warming above about 2,000′ during the night.  Most (light) showers should be in the form of sleet (ice pellets) or liquid rain.  So of course to get freezing rain you have to get surface temperatures below freezing.  Note the current temps:

2017 Current Temps PDX Metro Area Earth Scene

Thick cloud cover has moved in, stalling metro area temperatures right around the freezing mark.   We’re not going to see any significant additional drop.

The flow of cold/dry air out of the Gorge has weakened dramatically.  Only 3+ millibars PDX-DLS is not typical ice storm material for us.  It’s just a breeze from the east right now even in the usual windy spots; evidence the cold pool is shrinking and turning shallower eastside.

Dewpoints have also risen a bit, so if/when precipitation arrives, temperatures will only fall maybe 1-2 degrees with evaporative cooling.

That means almost none of us drop below 30 degrees.  Which leads me to believe that most roads which are thawed right now are unlikely to re-freeze tonight.  Freezing rain typically needs air temps down to 30 to get new ice on roads that aren’t already frozen.

SUMMARY

  1. It’s doubtful we see a widespread icing of already-thawed roads in the metro area
  2. There may be a few new spots of icing, but the main highways/freeways WEST of I-205 and south of Milwaukie/Happy Valley should be clear tomorrow morning.
  3. Frozen roads in the hills and east metro will remain that way through the morning commute.

We continue the slow thaw tomorrow with almost all roads in decent shape by late afternoon, still some ice east of I-205 though.

South wind arrives Thursday afternoon/night.  Until that time no dramatic warmup, just a slow thaw.  We should be around 50 by late Thursday evening.

Chief Meteorologist Mark Nelsen

 


S-L-O-W MELT CONTINUES, FLURRIES OR FREEZING RAIN SPOTS TONIGHT

December 26, 2017

2:30pm Tuesday

Temperatures warmed…slightly…today.  It appears the airport hit 34 or 35 degrees.  Snow & ice doesn’t melt fast, even with morning sunshine, at that temperature.  Cool air is still pouring out of the Gorge, although the wind is relatively light.  The airmass within the Gorge has modified a bit further, with Hood River now about 5 degrees warmer than before things got started Christmas Eve midday.

Rumors of more freezing rain, sleet, or snow abound; here’s the deal.

  1. IF this was a typical winter afternoon and the weather pattern was exactly the same but 40 degrees right now?  I’d forecast cloudy skies tonight with a few sprinkles or showers.  Then more widespread sprinkles or showers at times tomorrow.  There’s no big storm headed our way, just a few showers.
  2. But it isn’t a typical winter afternoon and temperatures will still be cold enough for either snow/liquid rain to stick or form a glaze on surfaces tonight IF PRECIPITATION ACTUALLY FALLS OUT OF THE SKY.  IT COULD REMAIN MAINLY OR ALL DRY.  I think it’s unlikely we get more than 1/2″ snow.  Just a dusting in many spots.
  3. Not all of the metro will see cold enough temps for frozen roads tomorrow morning.  Lots of cloud cover SHOULD keep some areas only right around freezing.

So here’s my forecast:

Mark Snow Metro Forecast

FOR THE AM COMMUTE

Mark Road Condition Forecast

  • I think there will be additional icy areas that were not there this evening, assuming showers do show up.  Expect lots of slippery areas in the West Hills and eastside where temperatures will be coldest.  We may not get a total freeze of roads westside, but ANYWHERE could see a dusting of snow or fresh ice.  With scattered showers it’s tough to know exactly where that happens.
  • Roads will improve a bit more tomorrow.  Today my drive on the freeways was just dry or wet in spots, no ice from Troutdale to Beaverton.  Actually out in Beaverton you wouldn’t even know there was ice/snow two days ago…almost nothing left except on barkdust/grass in spots.  But I know many areas eastside and in the hills still have ice on roads.  That should improve tomorrow.

By the way, Thursday and Friday we’ll be around 50 or above.   The cold weather is just about finished…More later.

Chief Meteorologist Mark Nelsen