6-7 Wet Days Ahead

April 21, 2014

11pm Monday…

The forecast for the next week is pretty clear; wet with cooler than average temperatures for late April.  This has been well-advertised on models and in forecasts, so I got my lawn mowed, burned some debris, and planted a few things that could use a week-long soaking.  Hope you all got anything taken care of that needs to be done outside too!

A chilly upper-level trough is about to move inland this evening.  It’s quite a pocket of chilly air; snow levels should dip down to around 3,000′ by sunrise.  Not a whole lot of moisture left at that time for big Cascade snowfall, but for the first time this month we should solidly white pass highways right at daybreak.

Then we’re into the showers/sunbreaks routine tomorrow as the strong April sunshine heats the ground, contributing to weak instability in the atmosphere.  With such a chilly air mass it’s possible you could see brief hail or thunder at your house if you live inland between the Coast Range and Cascades.

Wednesday and Thursday look WET!  Take a look at our RPM rain accumulation graphic:

MarkRain_RPM_NEXT24HOURS

Several surges of rain move through along with gusty southerly wind; looks more like early March than late April.  But we’ve been a bit above average so far this month temperature-wise so now it’s time to be a bit cooler (thus an “average”).

What about Cascade snow?  Quite a bit up around 5,000′, not too much below:

MarkHeadlines_SpringBreak

The milder than average temps the first part of April have accelerated the normal spring melt below about 5,000′ in the Cascades.  Note the snow water equivalent at 4,800′ Santiam Pass (Hogg Pass SNOTEL):

hogg

The solid blue line is this snow season’s SWE, the light blue is average.  You can see the plummeting values the first half of this month.

Up at the lower elevations of Timberline Ski Area at 5400′ the story is a bit better:

hood

With all the snow coming the next week at that elevation we’ll probably see the highest values of the season coming up, a “second peak”.  Interesting that at that site the average does linger at the maximum for a little over a month, then there is a quick fall-off as temperatures warm rapidly in late May.

Enjoy the rain…

There is some hope on the horizon.  Models give us at least some brief ridging about a week from now (NEXT Tuesday/Wednesday).  Take a look at the 850mb chart from the 00z GFS showing temperatures at the 5,000′ elevation returning to normal or a bit above after next Monday.

tseries_850t_000-384_Portland

You can see how the very warm 00z GFS operational run is quite an outlier.  I doubt we’ll be seeing a +17 deg C. temperature on the last day of April.  That would be a high temperature well into the 80s.  But it appears it will be warmer and drier right after our 7 Day forecast ends.  The 12z ECMWF was very warm as well and warmer than most of its ensemble members.  Here is the operational run showing high temps up around 80 at the same time:

KPDX_2014042112_dx_240

 

Chief Meteorologist Mark Nelsen