July 1st: One Day Heat Wave Ahead!

June 30, 2014

The next 48 hours should be fun as we see an abrupt switch to strong offshore flow (rare in July) tonight through Tuesday afternoon, pushing high temps into the mid-upper 90s in the valleys.  Then just as quickly we get a surge of wind off the chilly Pacific Tuesday evening through Wednesday, so high temps will drop 14-18 degrees in one day.  Further cooling Thursday means highs in the mid 70s.  So I think everyone can find something they like in the next 3 days.

The Details

  • We’re forecasting 97 for a high at PDX Tuesday, at least a 10 degree jump from today.  That is the warmest we saw last summer too.
  • That will be the warmest so far this season, we hit 91 back on May 14th, the first 90 of the year.
  • It will not be a record because there was a heat wave during this time in 1942 and we hit 105 on July 1st!
  • No high humidity…we’ll see dry east wind, our typical hot weather pattern.
  • Gusty east wind develops at the west end of the Gorge and over the Cascade foothills by sunrise, then it’ll surface in some areas in the lowlands
  • The Oregon Coast should be very warm, especially north of Pacific City, but light west wind after the noon hour should cap Lincoln City and Newport’s high temps below 80.
  • There is only one very warm and sunny day coming at the coastline…that’s tomorrow.

BMAC Summer Highs 10 years

 

June has not seen any temperature extremes, in fact until today (June 30th) we didn’t even get above 81!  A bit weird considering the month was average temperature-wise.  One would think at some point we would have seen an 85 or 90 but no.

Tomorrow’s forecast high temperature has been steadily creeping upward the past few days, partly due to confidence in a sharp thermal trough setting up west of the Cascades, but also due to 850mb temps warming in successive model runs.  The 12z suite of models (NAM, GFS, ECMWF) are all showing +22 to +23 deg. C over Salem tomorrow afternoon.  Looking at my chart of past cases with easterly flow at that temperature, we should see a high between 96-100 degrees, so my 97 might be slightly low.  Everything appears perfectly aligned for maximum heating tomorrow, including a drop off of the wind at max temperature time around 4-6pm.  There is even a chance we hit 100 tomorrow afternoon at PDX.

Since the upper-level trough is shifting east rather quickly later tomorrow and Wednesday, the center of warmest weather will shift quickly east of the Cascades tomorrow night and Wednesday.  That means a pretty decent onshore flow will immediately follow tomorrow’s offshore flow.  And that equals a quick cooldown.

The rest of our 7 day forecast has ridging to the east and upper-level trough to the west, with us in the middle.  That pattern will bring us the morning clouds and afternoon sun routine.  Here is a glance at the 12z ECMWF 850mb ensemble chart:

tseries_850t_000-360_Portland

Note the huge spike tomorrow followed by cooler temps through the 5th, then a bit warmer than average next week.  The GFS disagrees

tseries_850t_000-384_Portland

showing temps near average through the 8th, and the operational run is the chilliest of all the members.  So (normal operating procedure) I ignored the GFS.

Chief Meteorologist Mark Nelsen