If we can’t get “real” snow, this morning’s flakes are the next best thing!
After a very cold weekend, temps have warmed (slightly) here in the metro area a bit this morning; most of us are right around 30 degrees. The fog layer has lifted up into a low cloud (stratus) layer around 1,500′ at the base of the clouds. Radar just barely shows a little lifting of the low cloud layer has allowed flurries to develop and drop right over us. Here’s a link to the radar loop, but by 10am you probably won’t be able to see anything. In some spots it’s been enough to turn the ground white, not much different from a heavy frost, but it’s sure fun to watch it fall! Here’s a pic from Rian Muleback in Gresham:
The one thing that has changed this morning can be seen on the visible image,
the low cloud deck has lifted up and the top is now over 2,000′ ; that’s part of the reason temps are a little warmer at the lowest elevations and a little cooler higher up in our little “westside cold pool”. It’s really cold up on the TV tower, around 22 degrees at 1800, just about the coldest I’ve seen without arctic air or a cold air mass coming through the Gorge. The past few days have sure been interesting for the weather geeks with regard to the air mass temp! As a result today should just be gray and a couple of degrees warmer than the last few days. Maybe a high around 35-36 at PDX.
Check out what happens in the next 36 hours. Our 850mb temps go from this morning’s -5 to a +11 overhead! That means at 4,000′, temperatures which are in the mid 20s right now soar to 50 or so by Tuesday evening. Even a little warmer Wednesday. And the warming doesn’t really “move in” from anywhere, it is from subsidence. That’s subsiding warmer and very dry air as a strong upper-level ridge builds right over us. It’s a little tricky for forecasting, but here’s what I see happening… The subsidence warm and dry air will “dry up” the 1500-3000′ low cloud layer sometime later Tuesday (maybe not until after dark) and then a new much stronger inversion forms much closer to the surface. I could see the low clouds dissipating and then a new fog layer developing in the lowest 1,000′ of the atmosphere by Wednesday morning. If so, the foothills should be dramatically warmer Wednesday but we stay below 40 degrees here in the lowest elevations. This would be our more typical inversion setup. I think I’ve decided to call this the STRATUS REPLACEMENT CYCLE; inspired by the eyewall replacement cycle. There is no help from dry east wind the next 3 days, so if we stay clouded up or fogged in Wednesday, then we’re stuck in the muck. For several days, the WRF-GFS has shown this whole process quite nicely:
The green is relative humidity, and time goes from right to left. Look how the dry air works down later tomorrow and by Wednesday morning it’s extremely dry except right at the surface. SUPPOSEDLY it makes it all the way to the surface, or within a few hundred feet, but I’m assuming that will be wrong. And look at all the beautiful dry and warm air up above 1,000’…Spring skiing time!
What about the next 7 days and beyond? A snoozer… Next chance for real precipitation is still over a week away…
Chief Meteorologist Mark Nelsen