First Hot Weather

May 28, 2007

SnapshotIt’s very gratifying to take 3 days off work, come back, and find almost the exact same forecast you left the week before.  That’s the case tonight.  The cold trough that over the weekend moved through the Northwest is now into the Northern Rockies.  An upper-level ridge of high pressure is developing just to our west and it moves directly over the West Coast over the next few days.  This gives us another round of downslope easterly wind.  Of course in the warm season, this is a hot wind so today’s 68 degree high will be just a memory by tomorrow afternoon.  Remember that a couple weeks ago we went from 59 to 81 in just one day in the same quick switch from onshore to offshore windflow.  It appears that a thermal trough develops over the coastline by daybreak, then shifts over the Coast Range later tomorrow afternoon.  That gives a brief period of offshore wind even to the beaches in the morning.  That’s why I had such high temperatures in the Coastal forecast tonight.  Inland temperature forecasting is a bit simpler.  850 mb temp of +15 to +16 with "perfect" offshore flow (tomorrow), can give us as high as 90-91 at PDX.  However, I think the wind may be quite breezy even all the way to the airport, which can reduce heating, so I left it at 88.  Wednesday should be warmer since we still have easterly flow in the morning, then it goes calm in the afternoon.  But still no onshore flow at that point, so 91-94 is a good bet then.  A decent, but not major, marine push for Thursday drops us down into the mid 80s.  Same thing for Friday with a few degrees more cooling.
The weekend looks interesting with a sharp trough developing way offshore Saturday, then swinging onshore later Sunday.  That setup will pull the thermal trough back over the westside or at least over the Cascades for a warmer day.  Then when the trough arrives sometime later Sunday or Monday, we get a major marine push west of the mountains.  This will probably be one of those 20-25 degree one-day temperature drops.  Also, it can be a severe thunderstorm pattern east of the Cascades too.  Enjoy the warmer temperatures the next few days…I know my freshly sprouted corn and cucumbers will!  Mark