Temperatures have been limited the past few days due to heavy cloud cover. Our high temperatures on Monday, not having reached at least 100° through late afternoon, has apparently brought an end to Heat Wave #2. That event lasted 4 days with the highest reading of 106° last Friday. But even though one heat wave has ended, another one will begin on Tuesday.
Heat Wave #3 should start very hot on Tuesday with highs expected to soar well above 100 degrees. I'm expecting 106 to 109 degrees in the south valley on Tuesday with palpable humidity levels. The discomfort index is predicted to reach about 12, and that indicates extreme heat stress for a time during the afternoon. Both Tuesday and Wednesday will see extreme heat stress. Heat Wave #3 should persist through next Monday, but some moderation is expected for Thursday through the upcoming holiday weekend.
There will be a slight chance for afternoon showers or thunderstorms in the mountains, especially Wednesday and Thursday. But rainfall from the monsoonal moisture plume has been very light. The reason for this is our upper level wind pattern. The dynamics have been very weak, so that building cumulus clouds have not been encouraged by the wind pattern. There will be a slightly better thermodynamic pattern for a few thunderstorms, mainly in the mountains, for the middle of this week.
The huge upper level high pressure system bringing all this heat to the western US is now expected to shift east by this weekend. That will mark the start of a modest cooling trend into next week. Upper level winds will shift from southeasterly to southwesterly by the Fourth of July. That should summarily cut off our monsoonal moisture source. Consequently, I'm forecasting dry conditions with completely clear skies for this weekend into most of next week.
6-29-15 6:30 pm Chief Meteorologist MILES MUZIO