May Turns Wet; Metro Downpours Tonight

May 18, 2020

9pm Monday…

Suddenly it feels like a normal May weather pattern is back, like an old friend.  All of us have seen at least a bit of rain the past few days, but some of us have seen tremendous gully-washers.  This is overdue, not just because we’ve been dry the past 9 months, but we’ve had quite a run of dry May weather.  We’ve seen 5 consecutive years with drier than average May rainfallRain May Recently

We’ve seen measurable rain in Portland each of the past 8 days.   Yesterday afternoon/evening thunderstorms moved over the Salem area and Colton/Estacada/Sandy.  There were some 1″ totals around Colton at that time.  Then a weak “deformation zone” sat over the area this morning and midday.  That dumped up to 1/2″ rain in some spots around the Portland metro area.  Finally, a batch of showers moved south through Clark county and central/eastern Multnomah county this evening.  It appears that the area from Troutdale to Happy Valley was nailed with the heaviest rain totals.    This was the radar view around 7:45pm

KPTV 2017 Default Earth

Daily totals at 9pm look like this; these are from official airport locations

Rain Metro Today Databound

But these small/intense showers have dumped even more in a few spots.

Rain Totals Metro Area

The good news is that these showers are making up for what has been a very dry spring.  The bad news is that we have a lot of cloudy/wet weather ahead.  The cool upper-level trough over the Pacific Northwest right now heads east tomorrow

euronow

But by Thursday/Friday another cool upper-level low is right over the region once again

eurothursdaynight

In-between we get strong onshore flow both tomorrow and Wednesday.  This means almost solid cloud cover west of the Cascades, although not many showers.  Once we add in the showers Thursday and Friday from the new low, rain totals look something like this for the next four days

7Day Interactive 4

This will be a strongly “orographic” rain setup the rest of the week.  Areas just downwind from the Coast and Cascade ranges will be relatively dry (Hillsboro, McMinnville, The Dalles, Maupin).  But in the constant westerly flow the “upslope” areas will be wet…wet…wet.  If you live in the Cascade foothills or western Gorge, I hardly see any dry weather through Friday.  Yes, that sunshine in March, April and early May was nice, but it’s make up time now.

What about Memorial Day Weekend?  A weak ridge will be over us Saturday/Sunday then get “squished down” a bit toward Monday/Tuesday.  That means Saturday looks dry, but showers possible Sunday/Monday.  But that’s way out there in time.  We’ll nail down that weekend forecast as we get closer.

Enjoy the showers!