Friday, June 01, 2018

Look Ahead Into Early June

First a look at PW and SST as the new month starts. High values of PW (above for 13 UTC this morning) remain mostly south of 20 degrees north (i.e., near and south of Cabo Corrientes). Sea surface temperatures (below for today) indicate warm temperatures well into lower GoC, but temperatures of 30 C and higher currently extend southward from the mouth of the GoC. However, above normal SSTs prevail over a large region of Pacific to our southwest.

Second below shows CG flashes detected over Mexico for 12-hours ending about midnight last night (from Atmo and Vaisala). The Mexican thunderstorm activity has shifted northward over western Mexico, but still remains mostly in mountains along Continental Divide. 

The week ahead appears interesting - the 500 mb pattern (subtropical anticyclone currently over north-central Mexico) is forecast by the global models to evolve into a pronounced summer pattern as the high strengthens and shifts northward toward the Texas Panhandle by 00 UTC on 8 June (average forecast from the GEFS is below for that time - oranges indicate 500 mb heights about 100 m higher than average for this time of year).

This is an excellent mid-level pattern for thunderstorms - given moisture and Cape. During June this type pattern often brings increased moisture from the east and also up the river valleys of north-central Mexico. The mountains of southeastern Arizona, and especially Cochise County) can be the focus of very high-based thunderstorms that produce sprinkles, gusty winds, and dangerous dry lightning flashes. The actual onset of the low elevation, summer thunderstorm season (aka "the monsoon") usually begins when PW reaches above 30 mm for several consecutive days - which looks to be a ways off, but perhaps occurring earlier than usual because of the favorable positioning of the subtropical anticyclone.

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