I’m back at work this evening and it appears I missed nothing weatherwise the past week. Just rain and some mountain snow.
This first week of May sure looks interesting. The #1 thing we’ll all notice? Summer temps arrive Wednesday and Thursday. Then a chance for thunderstorms later Thursday and Thursday night both east & west of the Cascades. Last year we saw 9 days in the 80s in May, but we had a very warm spring.
In the short-term, a warm front moves overhead tomorrow…that means gloomy skies and drippy conditions at times. Temperatures will remain a bit below normal. Then on Wednesday a warm upper-level ridge builds overhead with the warmest airmass so far this season. 850mb temperatures reach +15 or +16…midsummer values for our area. The combo of thick cloud cover tomorrow and then the sudden break to sun Wednesday plus warming atmosphere means a dramatic jump in our temperatures here at sea level. We’ll jump at least 20 degrees in one day. We won’t see any records set since they are around 90 this time of year.
By the way, assuming we hit 80 on Wednesday as forecast, it’ll be the first time we’ve seen the first 70 AND first 80 degree day at once here in Portland. We have been close…on April 14th 1984 we hit 79 degrees in Portland and that was our first 70 of the season.
We don’t get any sort of decent offshore flow Wednesday or Thursday, which means we likely won’t reach the upper 80s; that’s possible with such warm 850mb temps in May.
There are two other parts to our mini warm spell; Humidity and Thunderstorms
Humidity: Plenty of moisture gets left by the warm front (along with our wet ground) so all models are pointing to relatively high dewpoints Wednesday and Thursday. That means a humid feel for our first warm spell and very warm nights. Low temps will likely be within a few degrees of 60 both Tuesday and Wednesday nights.
Thunderstorms: All models also develop strong instability in the warm and humid airmass later Thursday afternoon & night. This plus the southerly flow is usually a good setup for thunderstorms. We could see some good weather action! I’ll be keeping a close eye on that.
Chief Meteorologist Mark Nelsen