10pm Update

January 5, 2010

Gradient is increasing rapidly this evening with gusts to around 40 mph already at Troutdale and Corbett. I noticed the 12z WRF-GFS showed about 6 millibars at 10pm and that’s about where we are. Colder and drier air is coming south down the east slopes of the Cascades and Central Basin of Washington too. The main issue this evening for the Gorge is whether there is even any moisture left for freezing rain or snow by 4am or so. I notice our model and WRF-GFS dry out quickly after daybreak, so this may just be an event where we see very light amounts of snow and freezing rain out there and it really doesn’t turn into a big deal.

I see the NWS evening discussion mentioned the possibility of freezing rain even to the Metro area Thursday night or Friday. It’s definitely something to watch, but I’m not to excited about it since we don’t get a nice period of cold/clear nights to cool the valleys down.

Next week is looking a bit wetter, but not much cooler in the mountains. I see Timberline has seen well over 3″ of rainfall in the last 30 hours or so. We haven’t seen such a dump of rain at that elevation in midwinter for 2 winters!

Chief Meteorologist Mark Nelsen


Meteorological Fun Ahead

January 5, 2010

It’s still pouring in the Cascades this morning; I see Timberline Lodge has received more than 3″ of rainfall.  I don’t think that happened last winter and I know it didn’t happen during the cold snowy winter of 2007-2008.  Not a perfect pineapple express of course but plenty of very warm rainfall.  The rain will taper off tomorrow morning, but until then it stays very wet up in the mountains with a good surge coming through tonight.

As the rainfall finishes up, we get a glancing blow of arctic air from the big surge headed into the middle of the country.  Models have been very insistent on a dramatic surge of cold/dry air into the Columbia Basin this evening and overnight.  We go from no easterly gradient through the Gorge this evening to 10 millibars or so by midday tomorrow (see image on the left).  On the right you can see the WRF-GFS 5,000′ temp forecast and then you really see the reason for the wind.  Notice a 23 degree temp over Hood River and The Dalles at 5000′ but it’s about 20 degrees warmer over the westside?  So that thick pile of air cascades down into the Gorge west of Cascade Locks like a waterfall (a very loose analogy I know, but that’s how I think of it).  So obviously precipitation type after midnight tonight is a real pain east of Multnomah Falls.  It’ll probably be an instance where it’s light rain, then drops below freezing in spots in the western Gorge, then turns to all snow east of Cascade Locks.  Depending on the changeover time the east end of the Gorge could see an inch or six inches!  Tough call of course.  I do notice the meteogram for The Dalles and Hood River shows temps below freezing all day over there.  It sure wouldn’t hurt to get several inches of snow in 1/2 of the Columbia Basin either since we have many days of easterly wind ahead.

What about here in the Metro Area?  That rainy sloppy junk continues today and tonight, then we gradually just break up tomorrow as the rain ends by midday.  Should brighten up quite a bit later in the day with a bit of downsloping wind.  I’d give it a 10% chance of something frozen (freezing rain only) here in the Metro tomorrow morning, increasing to 50% chance just east of Troutdale/Gresham (Corbett, Washougal hills).  If anything the cold air will be slower to move in than expected.  Then it’s on to a windy and chilly day.  Temps will hold in the lower 40’s all day.  Gusts to 65 mph are likely at the west end of the Gorge and 45 mph Troutdale/Camas/Gresham.  Not sure if we get the “slop-over” of cold air down the west slopes of the Cascades; this model would indicate some.  If so, all of the metro area will be windy, not just east of I-205.  Either way we’re going from warm, humid, and calm today to chilly, dry, and windy tomorrow.

Chief Meteorologist Mark Nelsen