April Is Here; But Lots of Rain Ahead

April 2, 2018

7pm Monday

Spring Break is finished in Oregon, but now it’s Washington’s turn.  It appears both will turn out wet…not really a surprise if you grew up in this area.

I had a great time travelling through Idaho & Utah with my son (mountain biking), then met the rest of the family in Nevada.  Lots of red rocks and sunshine!  This is Gooney Bird rock along the “Mag 7” trail system near Moab, UT

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We had one last run-in with snow in the higher elevations this morning.  I woke up to a little slush left over on the deck and greenhouse at home.  I had mentioned on-air last night that some areas in Northern Clark county up through SW Washington, under heavier showers, could see sticking snow down below 1,000′.  It happened in a few spots.

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Lynn Hayes sent this pic from above La Center at 900′ elevation.

There is no sign of hilltop snow in the next 10 days.  In fact temperatures move uphill to more typical upper 50s and lower 60s for highs the next week…after tomorrow.  Here’s a confusing-looking chart from the ECMWF model.  But you can glean a few tidbits from it.  The lower section shows 6 hourly maximum temperatures for the next 10 days at Portland.  Time goes from left (right now) to 10 days from now on the right.  Note the uphill trend in general, with a peak around this Friday and next Monday.  The green is the average of all 51 “ensemble members” from that model.  The black is the actual operational model.  Ensembles are often safer because they even out any one member showing some sort of extreme high or low on its own.  On the upper half of the chart each thin horizontal line is one of the 51 members.  Note the areas of yellow/orange.  When you see a whole column of yellow, there’s pretty good confidence that day is going to make it into the 60s if the model is correct.  Note again that’s Friday afternoon and again Monday PM.  It’s a nice visual way to quickly isolate warmer days in the model run.

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A wet westerly or southwesterly flow will be over us Thursday through Sunday and it looks unusually wet for early April.  Check out rain accumulation at PDX from the same model:

ECMWF 12z Rain Graph Next 10 Days

You see the heaviest rain on Thursday, and again Saturday plus Sunday.  Don’t make any big outdoor plans for this coming weekend.  But at least it’ll be a “warmer rain”!

Mt. Hood just had a 7-15″ dumping from a winter storm last night, but now April warmth is going to turn much of the coming precipitation into rain.

ECMWF Snow Level From 850mb Temps LONG TERM

See the snow level going above the passes from tomorrow through Saturday?  That’s a lot of rain falling on top of the snow.  Rivers will be running high over the weekend, but there is still LOTS of storage available in the Willamette Basin due to the lower than normal snowpack.

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I see most of those reservoirs are a bit lower than normal for early April, so this coming weather pattern should top things off nicely.  Typically water managers aim to have the reservoirs at full summer levels by May 1st.

To summarize:  The first half of April looks like a soaker

Chief Meteorologist Mark Nelsen