A Week of Warm Afternoons & Chilly Nights

October 14, 2018

7pm Sunday…

Weather forecasting is VERY simple this next week.  A strong upper-level ridge of high pressure has moved over the West Coast and should remain in this general position through NEXT weekend.  This is what it looks like today overhead:

Jet Stream Forecast 2017 and next Saturday, not much change is there?

Jet Stream Forecast 2017_a

This is a very stable pattern, especially when I see the same thing on just about all the models and good agreement on the model ensembles themselves.

The east wind showed up, but far weaker than what models were showing Thursday night, the last night I was at work.  They were indicating 6-7 millibars easterly flow through the Gorge or at least from the Columbia Basin to Portland.  Instead it peaked at a paltry 4 mb. this morning.   Crown Point had a gust to 52 mph, weak sauce even for October

Wind Peak Gust Gorge Crown Point

We DID get the downsloping wind today though, dropping dewpoints well down into the 20s for many areas west of the Cascades.  There is one good way you can tell the difference between a regular “Gorge gap wind” and a more unusual downslope wind.  The wind direction with a typical easterly wind event in the cool season is ESE or even SE at PDX.  A downsloping-type wind is E or NE at that location; something I noticed early in my career here.  To summarize the weather pattern the next week?  We’re living in “Central Oregon” right now weatherwise; warm sunny days and cold nights.

This general setup continues through next weekend.  The result will be light frost in spots away from the wind tonight.  The Olympia to Eugene pressure gradient (northerly) is still around 5 millibars this evening which leads me to believe there will be areas of northerly wind at times all night in the Willamette Valley.  That also makes me think frost will be patchy.  We’re going to see some spots (in the breeze) stay in the 40s tonight and calm areas drop to around 30.

Forecast Tonight Metro FOX12PLUS

How much longer will we remain dry?  Models seem to want to break the ridge down early next week (around Tuesday the 23rd), bringing in more typical late October rains at that time.  Check out the rain on most of the ECMWF ensembles suddenly showing up at that time

KPDX_2018101412_eps_precip_360

The top chart shows each of the 51 ensemble members as a horizontal line with accumulating rainfall.  Notice almost all of them produce 1″ or more total rainfall by the 29th.  The average is 2.30″ or so, seen on the bottom chart.  So this EPS shows a very wet pattern for NEXT week.  I noticed the GFS doesn’t seem to want the ridge to disappear through the next two weeks; showing just a bit of a breakdown next week but it doesn’t totally go away.  I’m pretty confident we can forget any chance of a cool & wet pattern through the end of the month, but we may have a mild & wet pattern ahead!

Short-term, offshore (easterly) flow continues through Wednesday, then turns weakly onshore Thursday.  That upper-level ridge rebounding late Friday through Sunday gives us another round of gusty east wind.  Temperatures warm a few degrees tomorrow through Wednesday.  Back off Thursday/Friday with onshore flow, then models are pushing us up to +18 to +19 850mb temps Saturday…that would put us into the upper 70s!

Enjoy the sunshine!