Let the Heat Begin!

July 9, 2007

SnapshotIt’s very nice to take a few days off and have the forecast change very little during that time.  4 days ago we were wondering if the models were once again overdoing ridging for the upcoming week (right now).  Apparently they were right on this time…so…let’s have a heatwave.   I decided to blog early today since I don’t think much is going to change in the next 6 hours.
     Perfect setup for 100 degree weather west of the Cascades in the interior.  Drew Jackson reports from 7,000′ on Mt. Hood (hiking, but still with phone apparently) that easterly wind has already begun up there.  As those winds increase overnight, low pressure at the surface develops on the lee side of the mountains.  That means a thermal trough develops over the coastline since the easterly flow at 850 mb. will be strong enough to push all the way across the Coast Range.  With that in place tomorrow and 850 mb. temps forecast to be in the 23-25 degC. range, we should be able to just touch 100 degrees.  And even the coast will see easterly wind for one day, which means the beaches make it to 90 and areas slightly inland into the mid 90’s.  That makes for a very hot westside forecast.  The thermal trough is sitting from about Astoria to Eugene Wednesday morning, then slides east of the Cascades by Wednesday evening.  I’m assuming models are slightly fast on this with no obvious upper-level shortwave to suddenly shift it east.  That’s why I went slightly warmer Wednesday instead of cooler.  We should have a warmer start Wednesday too since the easterly flow continues all night tomorrow night in the Cascades.
Wednesday evening and Wednesday night could be fun since models are bringing a shortwave north along with moisture over the hot atmosphere.  Southeasterly upper-level flow has thunderstorms written all over it if you ask me.  And this pattern can bring storms all the way to the beaches too with all the instability above the chilly marine layer.  Assuming that we get a lot of cloud cover Wednesday night after a 100 degree day, I have a low temp near 70 since the clouds will bounce plenty of heat back down over us.

Something else sticks out on the Thursday-Saturday timeframe.  After that wave passes Wednesday night, upper-level heights stay very high through Saturday, so I think it’ll be a slow cooldown.  We’ll be above or near 90 through Friday at least with increasing humidity.  No good easterly flow or marine push to get rid of lingering low level moisture will make for a hazy/humid couple of days.  I wouldn’t be surprised to see 64-68 degree dewpoints after Wednesday for a day or two.  Of course I could be clueless, but that’s my gut feeling looking at maps.

Stay cool the next couple of days and hope for some good (wet) lightning the 2nd half of the week!  Mark