A Big Soaking For Some Tonight

May 11, 2015

Monday 5pm…

I was out working in the yard/garden this weekend and it’s pretty obvious we could use a soaking.  Here comes a night with some good downpours, but only for some of us.  The issue is that we don’t know exactly who is getting the soaking tonight; although we have a general idea it’ll be in the far northern part of Oregon and SW Washington.

An “upper-level low” will track from just off the central Oregon coastline at this moment to around Burns by tomorrow afternoon. The combination of moist southeasterly flow ahead of and to the north of it running into the northwest flow behind it will likely form what we call a “deformation zone”.  It’s a solid area of rain that develops in that location, generally north-northwest of an upper-level low.  Here’s the WRF-GFS rain forecast for the next 24 hours:

or_pcp24.36.0000

It’s soaking the Portland metro area with around an inch of rain, possibly even higher.  The pink area indicates 1.28″ or more.  The band of heavy rain appears to be centered from the central Oregon coastline across to Mt. Hood.

Our RPM forecast has similar, or slightly higher totals, but has the main action farther north.

RPM_12KM_Precip_NWOR

Notice just south of the metro area the totals are significantly lighter.

The HRRR model, which only goes out to 15 hours, has the soaking rains even farther north.

HRRR_RainTotal

Note only a few sprinkles south of the Columbia River by sunrise…seems too far north to me based on what we’re seeing on radar so far.

So the big picture is that a large area somewhere between Eugene and Olympia should get a soaking within the next 24 hours.  Regardless of the totals, Tuesday appears to be a rainy and cool day for most of us.  In fact I don’t see a good chance for dry weather activities (that need many hours of dry weather) until the 2nd half of the week.

MarkMowLawnForecast

We have two more upper-level lows that move inland over the West Coast, one on Thursday and one Sunday.  Both of those are moving into California, which means not a lot of rain here.  We could still see showers after Wednesday, but they should be far more spotty.

Chief Meteorologist Mark Nelsen