Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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280 FXUS65 KPSR 231700 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1000 AM MST Mon Sep 23 2024 .UPDATE...Updated 18z Aviation Discussion. && .SYNOPSIS... Strong high pressure will build into the region over the next couple of days resulting in a quick warm up and temperatures reaching well above normal by Wednesday. High temperatures topping 105 degrees are expected over a good portion of the lower deserts by Wednesday and likely lasting through the rest of the week. An Excessive Heat Watch has been issued for the Phoenix area for Wednesday through Saturday. Dry air will also remain entrenched over the area this week with clear to mostly clear skies persisting all week. && .DISCUSSION... Record high temperatures later this week are looking even more likely, particularly in the Phoenix area. The broad troughing over the region that has brought several days of cooler temperatures will begin to collapse today, while an unseasonably strong high pressure ridge shifts onshore across the Pacific Northwest and northern California. The ridge is then forecast to spread over all of the Interior West starting Tuesday with the ridge center tracking across the Great Basin. For our region, heights aloft will quickly rise into Tuesday allowing the heat to quickly build under continued dry atmospheric conditions. Forecast H5 heights for our area are expected to rise from the current 583-585dm to 587-589dm on Tuesday before even climbing a bit higher later this week. Highs today are likely to top 105 degrees over portions of the western deserts to between 100-104 degrees in the Phoenix area. As the ridge settles over our region starting Tuesday, even more of the lower deserts will see highs topping 105 degrees. Moderate HeatRisk will also expand over the majority of the area starting Tuesday. Over the past few days, NBM forecast temperatures have continued to trend up for this heat event, particularly for the latter half of the week. Starting Wednesday, NBM guidance now shows the majority of the lower deserts reaching between 105-110 degrees with expansive areas of Major HeatRisk across south- central Arizona centered over Phoenix. As a result, we have issued an Excessive Heat Watch for the Phoenix metro area from Wednesday through Saturday. Daily record highs for Phoenix starting Wednesday and likely through the upcoming weekend are likely to be threatened with NBM probabilities of tying records between 60-80% each day. Records in Yuma and El Centro are roughly three degrees higher than Phoenix during the period, so the probabilities of those two cities tying records are closer to 20%. This early fall heat episode will last for several days, likely at least into the weekend as the weather pattern becomes blocked with cut-off lows developing on either side of the ridge. The ridge center could meander a bit through the period, but ensemble guidance shows a high correlation of H5 heights staying around 588-590dm through at least Saturday, possibly longer. Some members are still trying to have the upper level low move closer to or even into southern California starting this weekend, but overall trends have been more toward keeping the ridge the dominant feature over our region into next week. At this point, it is difficult to say how long this heat episode will last, but there is at least some hope as the NBM highs for now start trending away from the 110 degree mark by around Sunday. Either way, we should keep temperatures well above normal into next week with little to no change in moisture levels. && .AVIATION...Updated at 1700Z. South Central Arizona including KPHX, KIWA, KSDL, and KDVT; No aviation weather concerns are expected during the TAF period. Winds will be light out of the E before becoming more variable during the afternoon hours. Low confidence exists regarding a W`rly shift this afternoon/evening, but if this were to occur, it would likely only last a few hours before winds switch back to the E again. Clear skies will prevail through Tuesday afternoon. Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns expected during the TAF period over the next 24 hours. Variable winds will eventually become established out of the W at IPL, while NE winds will shift out of the NW at BLH this evening. Clear skies will prevail through Tuesday afternoon. && .FIRE WEATHER... High pressure will build into the region over the next couple of days resulting in warmer temperatures and continued dry conditions. Above normal temperatures with lower desert highs topping 100 degrees are expected today with many locations topping 105 degrees by Wednesday, or near 10 degrees above normal. MinRHs will fall to around 10% over the lower deserts to 15-20% over higher terrain areas. Winds are expected to remain light through at least mid week, generally following diurnal wind patterns. Much of the same is expected through the rest of the week as the high pressure system keeps above normal temperatures and dry conditions over the region. && .CLIMATE... Record highs this week: Date Phoenix Yuma El Centro ---- ------- ---- --------- Sep 25 108 in 1989 112 in 1963 110 in 2015 Sep 26 108 in 1989 111 in 2010 110 in 2010 Sep 27 107 in 2009 111 in 1963 111 in 2009 Sep 28 108 in 1992 108 in 1994 109 in 2009 Sep 29 107 in 2003 110 in 1980 110 in 1969 && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Watch from Wednesday morning through Saturday evening for AZZ537-540>544-546-548>551. CA...None. && $$ DISCUSSION...Kuhlman AVIATION...RW FIRE WEATHER...Kuhlman CLIMATE...18