From the Central Valley of California to the deserts of California and Arizona and north into parts of Utah and Nevada, heat has been the main weather story for days. Records have been established. Both Fresno and Bakersfield, California, hit 110 F for the first time this year on Monday also setting records for the day. Phoenix also hit 110 F Monday and Las Vegas has been running 7-9 degrees above normal for the past four days.
The ridge that has caused this heat started to break down Tuesday in California allowing at least some cooling to get into the Central Valley. Well cooling is probably not the best word to use here. Let's just say it wasn't quite as hot. Highs Tuesday have been running 5 to 10 degrees below the extreme heat of Monday. More cooling is likely through Thursday, and the drop in temperatures to more normal early June heat is likely to spread into Nevada and Arizona over the next few days as well.
This map shows the 500 mb height anomaly over the next five days. Basically if you are in the red, heights are averaging higher than normal and one can typically expect warmer-than-normal temperatures. In the blue, heights are below normal and temperatures tend to run cooler than normal.
California and the Southwest being in the white means near-normal heights and thus near-normal temperatures. If you live in the Northwest, a cooler-than-normal pattern is in you future, probably starting on Friday.
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These is the possibility that another surge of tropical moisture could move into Arizona and Southern California by the middle of next week.
I still believe the greatest amount of rain, at least partially relating to Norbert, occurs from southeast California to Arizona
The effects on Southern California are very much in question.
With low wind shear and warm water in its path for a while longer, it is likely that Norbert intensifies into at least a Category 2 storm.
For much of the last week the monsoon moisture flow into the Southwest has been completely shut down by dry westerly winds. This is about to change.
A big pattern change is underway, one that will completely shut down any chance of showers and thunderstorms for an extended time period.