Today was the windiest day in about 3 weeks in the Northern Willamette Valley:
Combine that with clouds, rain a good chunk of the day, and cool temps and it sure felt more like early April rather than late May.
We get rid of the wind tomorrow, but keep the rest. Although I suppose the showers will be a bit lighter.
A cold upper level trough drops through the Pacific Northwest on Thursday; this is likely to give us a round of heavier cold showers with some hail or thunder. Lifted Index (measure of stability in an air mass) is right around zero all day Thursday…usually a very good sign, along with a chilly air mass, that we’ll see some active afternoon convection.
As that upper low drops off to the south Thursday night and Friday, we get a very dry northeasterly flow through the lowest 10,000′ of the atmosphere. This is very similar to a cold and dry northeast flow in wintertime as arctic air moves down behind an upper-level trough. But since we’re in the warm season, pressure gradients remain light through the Gorge and over the Cascades. So no gusty east wind. Just a breezy afternoon north or northeast wind here in the Portland Metro area. The result will be a 10-14 degree jump in high temperatures and a mostly sunny day.
Still some leftovers of that northerly flow Saturday for a second nice day, but then it’s back to onshore flow and more cloud cover for the 2nd part of the holiday weekend coming up. This is where I made a change to the 7 Day forecast this evening. The trend in models is to push a cool upper-level trough farther south into the Pacific Northwest by Monday. In fact 850mb temps around 0 to +2 are quite cold for May 28th…I sure wouldn’t camp in the Cascades Sunday and Monday unless I had some solid sleeping bags, gloves, and a hat to wear overnight. One more reason I don’t mind working Memorial Day Weekend most years. This year I’ll be here Sunday and Monday.
Each model and model run has been a bit different, but the trend is still there for a downhill slide weatherwise Sunday and Monday. I’m not real confident we’ll actually see measurable rain here in Portland, but it’s far safer to go a little pessimistic on a big holiday weekend and be surprised by decent weather than have things turn out the other way around. Here’s a graphic I used on-air tonight, the warmer temps refer to Friday and/or Saturday, the coolest temps on Monday:
Chief Meteorologist Mark Nelsen