Minor Heat Wave Ahead

It is almost like clockwork.   

Sometime in May, generally between the 7th and 20th of the month, there is a minor heat wave, with temperatures getting above 80F. 

And this year will be true to form, with temperature near 80F, or even the lower 80s, on Thursday, Friday, and Saturday.

 Don't remember the past May heat waves?  To jog your memory, take May 1997.  Spike to around 80F mid-moth,

 2016?   A jump to 87F!

 I could show you a dozen more of these, but you get the point.  After the mid-month spike, things generally cool down as we going into the doldrums of the June gloom period, characterized by lots of low clouds and temperatures in the upper 60sF.

Our "heat wave" is being forced by the development of an impressive  upper level "ridge" of high pressure and heights over the eastern Pacific.  Here are the forecast upper level (500 hPa) maps for 5 AM Thursday and 5 PM Friday.  Huge ridge over the eastern Pacific on Thursday morning and a trough of lower heights/pressure over California.

Later Friday, the ridge weakens a bit, but is still over us, while the trough has deepened over California.  Because of that. there will be some rain from San Francisco down to LA--which should help delay the wildfire season a bit.

This pattern will bring a warming atmosphere and offshore flow over the Northwest on Thursday through Saturday, resulting in substantial warming.  To show this, here is the National Weather Service ensemble (many forecasts) product for surface air temperature.   The many model runs are on the same page, indicating four days of warming, before temperatures start to cool on Sunday.

And don't worry about warm/dry conditions lasting forever.  Recent model runs suggest a major switch to cooler/wetter conditions after the 15th.

What do I think will be the smoke outlook for the summer?  That will be the topic of a future blog.






from Cliff Mass Weather and Climate Blog https://cliffmass.blogspot.com/2019/05/minor-heat-wave-ahead.html