Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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374 FXUS65 KPSR 040929 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 229 AM MST Thu Jul 4 2024 .SYNOPSIS... A very strong high pressure system will overtake the region over the next few days resulting in unseasonably dry conditions and even hotter temperatures. This will lead to excessive heat conditions building across the majority of the region starting today and likely lasting through at least the early part of next week as high temperatures across a good portion of the lower deserts reach or even exceed 115 degrees. && .DISCUSSION... A very strong high pressure ridge meeting climatological record H5 heights off the California coast of up to 599dm has overtaken the majority of our region. Very dry air has surged southward through southern California and all of Arizona except for the southeastern portion of the state. Aside from some very shallow boundary layer moisture reemerging since late last evening, daytime surface dew points will drop into the 40s to around 50 degrees this afternoon and then plummet to between 25-35 degrees on Friday. This amount of dry air will push PWATs down to as low as 0.5" in the Phoenix area on Friday, well below the 1.4" or above typically needed for monsoon activity. Given the very high heights aloft and the drying of the atmosphere, air temperatures will respond over the next couple of days with readings easily topping 115 degrees over much of the lower deserts of southeast California and southwest Arizona to 111-116 degrees across the south-central Arizona lower deserts. The hottest day is likely to be Friday when we see the lowest dew points. It would not be surprising to have some areas west of the Colorado River reach 120 degrees on Friday. This building heat will cause the areal coverage of Major HeatRisk to expand considerably through Friday with the majority of the lower deserts crossing over the threshold considered for excessive heat. Forecast temperatures through at least next Tuesday do not vary much more than a couple degrees with highs each day generally ranging from 113-120 degrees across southeast California and far southwest Arizona to 111-116 degrees across south-central Arizona. Lower level moisture is likely to rebound slightly over the weekend into early next week as we get brief bouts of moisture off the Gulf of California, but all that will do it make it feel a little less dry. Clear skies are likely to persist through the weekend and possibly longer depending on how the proximity of any storm activity over New Mexico and far southeast Arizona. The strong high pressure ridge is forecast to very slowly shift eastward through California reaching western Arizona at some point early next week, but it will also weaken some during that period. H5 heights for our region should stay very steady at between 594-596dm through at least early next week, likely longer. As the ridge center moves into Arizona (likely northern Arizona) by the middle of next week, this should allow for some additional moisture to begin seeping into southeast Arizona to as far north as the Mogollon Rim. This should provide for a modest return of showers and storms over the higher terrain as early as next Tuesday, but that timing may be a bit optimistic. A north to northeasterly steering flow will likely prevent any activity from reaching the south-central Arizona lower deserts for the first few days, but gradually (late next week or next weekend) chances may spread into the Phoenix area. Forecast temperatures during the latter half of next week do gradually lower, but it still seems probable that the Excessive Heat Warning will have to get extended further, especially across the western deserts. && .AVIATION...Updated at 0505Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major weather issues will exist through Thursday night with daytime cloud decks relegated to mountains well east of the terminals. West winds should predominate for the majority of the TAF period with only a brief period of light easterly or variable winds around sunrise. Occasional gusts up to 20kt will be possible. Southeast California/Southwest Arizona including KIPL and KBLH: No significant weather concerns will exist through Thursday night under clear skies. A SE wind component will be preferred at KIPL with some variation between SE and SW at KBLH. Occasional afternoon/early evening gusts around 20kt should be expected. && .FIRE WEATHER... Hot and dry conditions will prevail across the area through at least the weekend as strong high pressure settles in from the northwest. Excessively hot temperatures with highs generally between 112-117 degrees are expected across the lower deserts each day through early next week. Daily MinRH values through the weekend will fall between 5-15% across the lower deserts, while higher terrain areas in Arizona will mostly see 10-20%. Winds will follow diurnal trends, occasionally gusting to 20 mph during the afternoon hours. The combination of the very hot and dry conditions will lead to an increased fire danger threat. && .CLIMATE... Record Highs Phoenix Yuma El Centro --------- ------- ------------ July 4 118 (1989) 117 (1957) 117 (1969) July 5 116 (1983) 116 (1905) 115 (2007) July 6 116 (1942) 117 (2018) 118 (1966) July 7 118 (2017) 118 (2017) 121 (2017) July 8 115 (1985) 118 (1958) 117 (1942) July 9 116 (1958) 119 (1958) 117 (1958) July 10 115 (1958) 118 (1959) 116 (2021) && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Tuesday for AZZ530. Excessive Heat Warning from 10 AM this morning to 8 PM MST Tuesday for AZZ531>555-559. CA...Excessive Heat Warning until 8 PM PDT Tuesday for CAZ562-566-567- 569-570. Excessive Heat Warning from 10 AM this morning to 8 PM PDT Tuesday for CAZ560-561-563>565-568. && $$ DISCUSSION...Kuhlman AVIATION...18 FIRE WEATHER...Kuhlman CLIMATE...Kuhlman