The well advertised heat wave is still on track to hit with a vengeance starting Sunday, and lasting through the middle of the upcoming week. Current forecasts show record breaking temperatures likely for Sunday-Tuesday. However, there are a few interesting features that could hinder temperatures from reaching that toasty 120 degree mark. More on that shortly.
SATURDAY AND SATURDAY NIGHT
The center of the building high pressure system responsible for the heat is over Southeast Arizona, with a slow movement to the west and north expected through Tuesday (as depicted by the dotted yellow line below) . The circulation of wind around this high pressure cell (depicted by the red arrow below) is bringing an increase in high level moisture and clouds across our area today. This has helped keep most areas under 110 degrees so far today.
Periods of high and mid level clouds will continue the remainder of today and tonight. The airmass in the lower levels is extremely dry, with dewpoints in the 20's and 30's today continuing into tonight and Sunday. Some computer models show a slight amount of instability associated with these clouds tonight and Sunday morning. This could be enough to create some virga (rain falling from the clouds but evaporating before it hits the ground), or even a random stray sprinkle or bolt of lightning at some point tonight or early Sunday. Most likely it will simply create an amazing sunset and sunrise.
Sunday should see a 5-10 degree jump in temperatures. Highs are expected to climb to 112-118 degrees. The only caveat that could save us from reaching the high end of this spectrum is if the clouds linger a bit longer into the morning or early afternoon. If they do, it is likely temperatures will remain under about 112-114 for most areas. Otherwise, expect a hot and dry day with low humidity. Low temperatures Sunday night should be toasty 79-89 degrees.
Monday will likely be the hottest day of this heat event. With sunny skies and dry air in place, temperatures are expected to reach 117-122 degrees. Low temperatures should be 80-90 degrees. The highest temperature ever recorded at PSP in the month of June is 122 degrees.. so there is a remote chance we could reach that. Stay hydrated and out of the sun during the afternoon and evening hours if possible.
TUESDAY AND WEDNESDAY
By Tuesday and Wednesday, the high pressure system should be centered over southern Utah. This should allow upper level winds to shift to east or southeast. High temperatures are still expected over the deserts, but two factors MAY come into play that could take a bit of the edge off the temperatures and drop us back into the 108-118 range, or possibly a bit lower depending upon what plays out.
First, there is the possibility a weak system, currently near Louisiana, could get entrained in the easterly flow and move west through Arizona and Southeast California. If this occurs, we could see increased cloudiness once again and increased humidity by Tuesday night.
Second, low level humidity levels are rising along the west coast of Mexico, with dewpoints into the 60's and 70s up and down the Gulf of California (associated with the beginning of the yearly "monsoon", which is a wind shift to the southeast that occurs each summer in this area). Southeast flow may allow some of this more humid air to flow north, with some indications it may reach the deserts around Tuesday or Wednesday.
Together, these two factors could allow temperatures to drop into the 103-110 range, instead of the 108-118 range currently predicted. The increased moisture would be more uncomfortable, with higher dewpoints possibly rising into the 50s, 60s or 70s, and even a remote chance of an isolated shower or thunderstorm. These two factors will be watched the next few days to see if they need to be added into the current forecasts for next week.
Moral of the story - it's hot, use common sense, drink more water than usual and don't walk pets on hot pavement in this type of extreme heat.
Enjoy a pool or an air conditioned space and hunker in for the next few days!
And as a sidenote, the summer solstice is on Monday, June 20th at 3:34 pm. This means we get to enjoy 14 hours and 25 minutes of daylight. We also get to enjoy a full moon that coincides with the summer solstice.... something that doesn't happen all that often!