Nice Week Ahead: Memorial Day=Uncertain Forecast

May 19, 2014

6:00pm Monday…

We’ve got an easy forecast for the next 3-4 days…lots of sunshine and warmer than average temperatures.   Enjoy the nice workweek again!

PLOT_Rain_Metro_Autoplot_YESTERDAY

Quite a soaker for some us on Sunday as the cold upper-level trough moved through.  Some areas saw thunderstorms with downpours and even hail.  It appears the middle and eastside of the metro area got the biggest soaking.  Portland’s total was a record for the day, and the wettest day since early March.  That’s heading away from us now, replaced by a weak ridge of high pressure that peaks over us on Thursday.

Here’s the issue with the 4-7 day part of the forecast;  another cool upper-level trough approaches the Pacific Northwest this weekend.  So in general the weather appears to head downhill from Friday through Monday.  At least that’s what the GFS is showing.  First chance for rain on that model is Sunday, and Monday too of course.  Here’s the 18z GFS model ensemble chart, showing the 20+ different ensemble members’ temperature at 5,000′.

tseries_850t_000-384_Portland

It shows pretty decent agreement on the cooling temps with the approaching trough.  If this is correct, camping at those 4,000′ elevation mountain lakes will see high temps from from 50s Saturday to 40s Sunday and Monday…Brrr!  Of course that would be a wet 40s!

The ECMWF is a bit different.  Take a look at the 500mb map for Friday.  ecmwf_fri  It brings a piece of that cold trough swinging by just to our north Friday, giving us a few sprinkles/showers even on Friday.  But then it deepens the main trough farther offshore, building a temporary ridge with much higher heights overhead Sunday:

ecmwf_sun

Then the Sunday chart showing the temporary ridging and 580dm heights.

ecmwf_sun

That would say warm weather with temps in the 60s and some sun camping up there in the mountains.  Probably highs well into the 70s here in the lowlands too.  This is where the ensemble chart can be useful…from the 12z ECMWF:

tseries_850t_000-360_Portland

Wow, look at the spread suddenly developing starting on Saturday!  By Memorial Day itself, a good chunk of the ensemble members show 850mb temps around +1 to +6, the cool weather pattern the GFS is showing.  But there are about a third of the members showing anything from +8 to +20!  That’s why I say the weekend forecast is very uncertain.  My gut feeling is that the slowly approaching trough is the best bet, more like the GFS.  So our 7 Day forecast reflects that right now.

By the way, I’m pretty confident it won’t be THIS bad during the upcoming weekend…remember these downpours?

MarkMemorialDay_Rain_Records

You can go back through the weather blog archives and check out details on each of these events over on the right side.

More tomorrow when the forecast (I hope) becomes more clear…enjoy the sunshine during the week!

Chief Meteorologist Mark Nelsen