From 90 degrees to 100% chance of rain in Seattle in the same week?

Sun fans have sure had their fill these last couple of weeks with Seattle notching its second 90-degree day of the year Tuesday. That was the peak and while it’ll still be fairly hot Wednesday in the Seattle/Puget Sound area with highs in the mid-upper 80s, we’ll cool down to around 70 for Thursday as marine breezes kick in.

And then, fellow rain fans… feel like it’s our turn? There’s an unusually high amount of confidence that indeed, we’re about to flip to the other, wetter side of the meteorological coin for Friday and the weekend.

How high of confidence? How does 100% chance sound?

100% CHANCE OF RAIN? IN JUNE? REALLY? I DON’T EVEN GIVE 100% ODDS OF SPELLING MY NAME RIGHT

Indeed, the National Weather Service in Seattle in their Tuesday afternoon forecast update lists their probability of precipitation (POP) for Thursday night and Friday-day at 100%.

A low pressure center is forecast to come into Western Washington on Thursday night into Friday and spin through the area into the weekend.

It’s been consistent in the forecast models for the past few days and there’s enough rain in the forecast that measurable rain should be easily achievable.

But I have to admit seeing *100%* chance in summer is… well, exciting for one. But seems rare. We see 100% chances on those forecasts when we get our big atmospheric rivers in the fall and winter, but most storms I’d say usually come in around 70-90% juuuuuust to hedge. There was one time a few years ago when I was covering a landfalling hurricane for the Southeast and an NWS office under Hurricane Warning STILL only went with an 80-90% chance of rain that day (Fun fact: It, um, did indeed rain…) But I don’t really remember 100% POPs very often in the summer here, even on our rainy day forecasts.

BUT IT JUST MIGHT BE WARRANTED!

The 100% doesn’t mean it’s going to be particular stormy or a potent storm, just illustrates a good confidence it’ll rain…something. And I agree that the models are themselves VERY confident.

Pick the European Model or the American GFS, going back their last four ensemble runs which combined would be 320 model calculations, and ALL 320 show plenty of measurable rain in Seattle with this system. Not one says “nope”. And they’re all pretty equal on the amounts – -the Euro a little wetter at about 0.40-0.50 inches of rain in Seattle by Sunday; the GFS a little drier at closer to a quarter inch.

SO *WHEN* IS IT GOING TO RAIN?

The rain will first start along the coast Thursday evening then push into the Seattle/Puget Sound area overnight Thursday.

Friday will feature widespread light to moderate rain through the first half of the day, then move to more showery weather, though this looks like a pretty robust Puget Sound Convergence Zone will keep rain going in the North Sound into Friday night and even early Saturday.

There is even a chance of thunderstorms inside the Convergence Zone areas Friday evening/night so those between Seattle and Everett need to keep tabs on the skies. Anyone going to the World Cup match that night will also need to pay keen attention though the zone may stay just to the north of the stadium.

It will also be about as far on the cold end of the summer temperature spectrum as we’ve been on the hot end to start the week. After just missing a record high Tuesday (high was 90; record was 92), Friday and Saturday’s highs are in the low 60s — within shouting distance of setting a record for lowest high temperature for the dates (62 degrees both days.)  100% chance of BRRR or AAAAH depending on your perspective.

Showers will linger on Saturday though be fewer in number and coverage than Friday. We could eke out a mostly dry day Sunday — still can’t rule out a few stray showers.

Another much weaker system may toss a few scattered light showers our way Monday and Tuesday but its main effect will be just to keep highs in the 60s.

The long range forecasts do show a drying and warming trend as we head toward the 4th of July holiday but so far fairly moderate with highs in the 70s. And really, getting a nice soaking rain just days before the 4th is really something I’d think 100% of us can get on board with.

-Scot Sistek

(D’OH!)