Back to a White Christmas

December 24, 2017

7pm Christmas Eve

Merry Christmas from the FOX12 Weather Team!  Today has sure been a challenging day for us.

WHAT WORKED OUT RIGHT TODAY

  1. Cold air remained in place.  Temperatures stayed near/below freezing in most of the metro area as cold east wind kept coming out of the Gorge.
  2. 1st band of light precipitation came in as freezing rain/sleet/snow mix 9am-Noon.
  3. 2nd main band of precipitation arrived in mid/late afternoon as expected.
  4. West Hills and east metro roads remained frozen as expected.
  5. Typical west and south metro life resumed since roads turned mainly wet.  The shopping center near the station here on the westside was a zoo at 2pm.
  6. All roads central/eastside remain a frozen mess this evening as freezing rain has returned for many spots.  With the cold air we knew that would happen and I mentioned that this morning.

WHAT WENT WRONG (IN A GOOD WAY!)

  1. The 2nd band of precipitation was mainly snow instead of a mix.  That’s because  warming wasn’t as much as expected a few thousand feet up; the snowflakes didn’t melt into rain drops on the way down.  A trace to 2″ snow fell across most of the metro area (lightest west and heaviest east).
  2. I figured some snow would fall in north metro (Clark/Columbia counties), but not that much.  It was snowy all day up there with 2-4″ on the ground now.

Of course hardly anyone would complain about getting frozen precipitation in the form of snow instead of freezing rain, especially on Christmas.  As of 5pm the official snow total was 0.6″ in Portland, I’m guessing that will be higher when they measure later.

Latest temps show almost all the metro area is below freezing and it’ll stay that way tonight with no change in the low-level airmass.

2017 Current Temps PDX Metro Area Earth Scene

We’re into light off/on showers the rest of the night with a mix of freezing rain, snow, & sleet.  South of the Columbia River with thinner cold air above I think we’re mainly done with accumulating snow.  Once you get south of Wilsonville it’s a little too “warm” for anything frozen tonight.

MarkWarningsWinterWeather Polygons

North of the Columbia River more than likely it’ll remain as snow.

MarkWarningsWinterWeather Polygons2

The ice/snow that is on roads now isn’t going anywhere and will still be there when you wake up Christmas Morning.  With precipitation ending after sunrise, it should be a quiet weather day with temperatures gradually rising into the upper 30s.  That means a slow thaw with decent road conditions AFTER the noon hour.  Plan to visit friends during the afternoon/evening hours, not in the morning.

Chief Meteorologist Mark Nelsen

 


It’s Christmas Eve! Silver Christmas For Parts of Metro Area

December 24, 2017

8:30am Sunday

For the first time in about 20 years I’m sitting here on Christmas Eve figuring out how a “classic” snow/ice event will proceed for the Portland metro area.

Of course in 2008 we had all the snow on the ground and expected a little more the next day, that was easy.  You have to go all the way back to 1998 to find a couple of inches of morning snow Christmas Eve; then it melted by evening as the cold east wind died.  This time it appears the cold air is here to stay THROUGH TONIGHT.  That’s a problem for many of us in the metro area and Gorge.  It’s also a change from my post 24 hours ago.

RIGHT NOW

A band of light precipitation is moving through the North Willamette Valley and into the south metro area.  It appears to be mainly rain/freezing rain with some sleet (ice pellets) mixed in.

Temperatures are near/below freezing throughout the metro, Willamette Valley, and of course in the Gorge.  A layer of cold/dry air pouring out of the Gorge is about 2,000′ thick in the metro and thinner south of us in the valley.  It’s a few degrees colder than I was expecting.  Where it is above freezing (by 1-4 degrees), the air is dry enough that when moisture falls into it, temperatures fall (evaporative cooling).  This means ANYONE could get frozen precipitation of some sort the next few hours from Longview to Salem/Albany.  This part of the forecast hasn’t changed.  We thought there would be scattered icy areas if/when that first band of precip arrives.

THE MAIN MESSAGE

Models are bringing in this afternoon/evening’s system a bit farther south, prolonging the period that at least 1/2 of the metro area will get freezing rain (and icy roads) the next 24 hours.  It appears more of the metro area will see freezing rain than I was thinking 24 hours ago.

WESTERN VALLEYS FORECAST HIGHLIGHTS

  • Oregon Coast will be too warm for frozen precipitation, all clear out there
  • After patchy areas of freezing rain this morning, some weak daytime “heating” in much of the Willamette Valley south of a Newberg-Wilsonville-Sandy line will be enough to keep roads mainly clear through tonight; temps will hover just above freezing.  AFTER late morning, most of the Willamette Valley should be done with icy roads.
  • IN the metro area the cold temps mean precipitation with this first band could ice up roads anywhere before noon.  As we go through midday and early afternoon, main roads should be fine away from the Gorge as pavement temperatures stay above freezing.  Near the Gorge and in the West Hills icy areas will stick around all day.
  • After sunset and into this evening, more solid precipitation arrives.  It should be mainly freezing rain across the entire eastern half of the metro area north of Oregon City and in the West Hills.  Expect widespread icy roads for all these areas through the night and into Christmas Morning.  A Silver Christmas for many of us tomorrow morning.
  • West of the West Hills and Clark County there may be more snow mixed in with slightly deeper cold air.  Temperatures may go a few notches above freezing.  Ice on roads should more patchy in those areas.
  • Christmas Day temperatures will gradually go above freezing and ice even near the Gorge will melt off.  High temps reach into the upper 30s.

IN THE GORGE

  • Light snow arrives midday, then picks up a bit this evening and overnight.
  • Expect 2-4″ fresh snow central/east Gorge
  • West of Multnomah Falls, it’ll be more freezing rain & sleet than snow.  Expect glaze ice on roads around Cape Horn and Corbett/Bridal Veil areas as we go into the overnight hours
  • Not much melting Christmas Day since cold easterly wind will just weaken a bit.

 

There are 2 reasons the forecast has changed back to more ice the past 24 hours.  First is that the cold air pouring through the Gorge is a few degrees colder than expected.  That gives more of us an “opportunity” to enjoy frozen precipitation.  And second, sure enough the ECMWF model is looking like the smarter one, bringing in low pressure farther south.  Check out morning WRF-GFS low position at 10pm this evening:

There it is…right around Tillamook.  This is far enough south to keep the cold easterly wind going in the metro area through the night.  But it’s also just far enough north to push mild air over the top of the cold air, that mostly eliminates the snow chances keeping our precipitation in mainly a liquid form.  Of course that liquid can refreeze into sleet (ice pellets) or freeze on contact (freezing rain).  Notice there is no southerly wind in the metro area even by 7am Christmas morning; temps will rise a couple of degrees in the valley overnight, but we’ll stay frozen through the entire night in that easterly flow out of the Gorge in the entire eastern half metro area.

Be careful on the roads today and if you live on the east side of the metro area I’d plan to stay at home this evening through Christmas morning.

Chief Meteorologist Mark Nelsen