Ice Storm Near & In Gorge Tonight

January 17, 2017

10:15pm…

At least the forecast ice thickness panned out, but just in a much smaller part of the metro area.  Check out how thick the ice is!

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…An inch of freezing rain in just about 8 hours in Troutdale.  There could easily be 1/2″ additional before temps rise much more by sunrise.

Farther into the Gorge the ice storm continues through Wednesday, likely going slightly above freezing at the west end though.

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Chief Meteorologist Mark Nelsen

 


5pm: Most of Metro Dodges Ice Storm

January 17, 2017

It’s become clear the past two hours the very cold air pouring out of the Gorge is very shallow, more so than we expected.  The result?  Even most eastern metro locations will NOT be seeing a big ice storm tonight (Whew!) Sub-freezing air is mainly confined to right along the Columbia River and doesn’t extend more than 1-2 miles north and south.  You can see that in the latest temperature map, blue temps are below freezing.

plot_temps_nolabel_metro

Where the temperatures are below freezing, the ice accumulation has been very thick so far:

markfreezingrain_icetotalssofarpdx

That’s almost 1/2″ in Troutdale already.  If temps were 2-3 degrees colder eastside, this would have been the case for many more of you.

So only the areas right along the Columbia River will see additional icing tonight and of course it’s a big ice storm in the Gorge.

There will be no refreezing of roads tonight and the AM commute should be just fine (ice-wise) everywhere except right in downtown Troutdale and into the Gorge.

For the geeks like me…the Troutdale profiler shows us what’s going on.  The cold layer is VERY thin, less than 1,000′ deep over the west entrance to the Gorge!  Looks like abourn 50 degrees at the 2,000′ level.  Typically in a normal ice/snow event (even for east metro), the cold layer is around 1,500 to 2,000′ thick.  I thought it looked a bit strange this morning, but now we know what happened; something to remember for future storms.  A cold layer that thin, even with 10-11 millibars easterly flow,  will remained confined quite close to the Columbia River.  It is still 20-21 at Hood River and The Dalles, which typically would keep the entire east metro below freezing with the east wind.  This makes me think the current setup (cold air right along the river) could continue through the night and into midday Wednesday.  It’s still going to be a huge ice storm, but only in a very narrow ribbon along the Columbia River, both north and south.  I-84 will be close for a day or two I think.

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Chief Meteorologist Mark Nelsen


2pm: Heavy Rain is Here, Ice Storm East Metro

January 17, 2017

That accelerated quickly!  Moderate to heavy rain suddenly arrived in the metro area in the past hour and now ice is accumulating (technically accreting) where temps are below freezing.  I-84 immediately closed in the Gorge.  1/2 hour before that time I drove it westbound just as rain beginning and there were a LOT of semi-trucks flying through at 50-60 mph.  I’m guessing that didn’t go well once the heavy rain started at 25 degrees.  Where will the ice storm continue?  Take a look at the map:

plot_temps_nolabel_metro

Yep, in the areas exposed to the cold east wind coming out of the Gorge.  The cold air is only 1,000′ over Troutdale.

HIGHLIGHTS

Within the blue area above an ice storm has begun and will continue tonight.  Remember that temperatures have to be below 31 degrees for roads to turn icy, so in much of east Portland this will be a damaging event for trees/powerlines but not terrible on the roads.

ALL OTHER AREAS west of the Cascades are IN THE CLEAR for additional icing on roads.  This includes all of north/west/south metro areas.  Once you go south of the Multnomah County line in the east metro area you are mainly out of the freezing air.  You can resume your normal activities in those areas

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markfreezingrain_icedetails3a

Chief Meteorologist Mark Nelsen

 

 


9am: Incoming Showers = More Spotty Freezing Rain

January 17, 2017

I hope most of you in the central/east part of Portland chose to skip work/school today!

That first band of freezing rain passed through the metro area before sunrise, but was light enough that most roads don’t appear to have been affected much.  Don’t be fooled, check out radar…

Here come more showers and they look quite wet this time!  They are sneaking in due to that ridiculous huge gap in the radar coverage off the Oregon Coast.

codnexlab-nexrad-rtx-n0q-20170117-1656-024ani

Except for the timing of the heavier rain speeding up, the rest of the forecast is still on track.  Let’s check current temps:

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I hope you enjoy my graphics talent…  The yellow shows the areas that are at risk of widespread road icing BEFORE NOON.  This is roughly the “blue area” I showed on-air last night and in the previous blog posting.  This is going to quickly become an event centered on those areas that typically see cold outflow from the Gorge.  I find it very interesting the top of Mt. Scott appears to be busting out of the cold air.  This tells me the cold layer is VERY shallow and will mix out easily anywhere in Clackamas/Washington/Clark counties.  I left Clark county in the “scary yellow box”, but even there after noon it should be warming above freezing.

To summarize

  1. In the next two hours a light glazing of ice is still possible anywhere in the metro area still below freezing.
  2. But for a large part of the metro area (outside of yellow area above+most of Clark County), you will be “in the clear” after the noon hour.
  3. Ice Storm is still on for central to eastside of metro area…roads likely turn very icy the next few hours there.
  4. Loading of ice on trees/powerlines will become a big issue this evening and tonight east of I-5 in Multnomah County, especially east of I-205

Chief Meteorologist Mark Nelsen