Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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659 FXUS65 KPSR 252005 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 105 PM MST Wed Sep 25 2024 .SYNOPSIS... An unseasonably strong high pressure system building over the region will strengthen through the weekend bringing a return of excessive heat to much of the area. In fact, temperatures resembling the middle of June will be more common through early next week. Dry air will also remain entrenched well into next week resulting in mostly clear skies and a lack of rainfall. && .DISCUSSION... High amplitude ridging has now become established from the SW Conus into southern Canada with a blocking pattern across the southern tier of states ensuring this feature will move little through at least the middle of next week. Objective analysis depicts H5 heights very near 588dm early this afternoon with the high pressure center over southern Colorado. As a shortwave and jet energy lifts from the Pacific NW over the ridge axis into southern Canada in the next 48 hours, models are in excellent agreement depicting modest retrogression and strengthening of the positive H5 anomaly upwards of 592-594dm with the anti-cyclone center settling directly over the CWA. Correspondingly, ensemble guidance remains resolute showing H8- H7 temperatures reaching at or above the 99th percentile leading to surface readings at or above daily records. Numerical guidance remains very narrow advertising high temperatures 8F-15F above normal through the remainder of the week with the most anomalous heat occurring Friday and Saturday. Undoubtedly, a prolonged string of records will be broken at Phoenix Sky Harbor including the latest 110F in the period of record, with more scattered daily records in Yuma given the higher record thresholds. With a zonal northern stream jet retreated into southern Canada and a continuation of blocked southern Conus flow, little will change in the synoptic pattern through the first half of next week. A majority of ensemble members indicate H5 heights at or above 590dm being maintained over the forecast area with little impetus available to budge this anti-cyclone. The official NBM forecast continues to play catch-up to match the synoptic pattern with each successive run prolonging the excessive heat temporally. Thus, even though the official forecast depicts slightly lower temperatures during the first part of the week, it is very likely forecasts will continue to trend upward the next several model runs likely resulting in an eventual extension in the Excessive Heat warnings. Already in the latest model output, more expansive areas of major HeatRisk are evident through Tuesday and an extension in time and space will probably be realized within the next 24 hours. There is some ensemble support that Pacific energy will partially dislodge or dampen the subtropical ridge during the middle and latter half of next week finally bringing an end to the excessive threshold, but possibly not relieving the region from above normal temperatures. Nevertheless, there is no indications of increased moisture over the next 7-10 days and rain chances should continue to stay near 0%. && .AVIATION...Updated at 1740Z. South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Easterly winds, with speeds aob 8 kt, will continue before becoming more southeasterly early this afternoon. Early this evening winds may favor more of a northwesterly component before going westerly for a few hours this evening. Winds will be light and variable at times, especially around wind shifts. Winds will then go back easterly during the overnight hours. Skies will be mostly clear with FEW-SCT clouds with bases around 12-14 kft. Southeast California/Southwest Arizona including KIPL and KBLH: Extended periods of light and variable winds will continue at both terminals. A period of light southwesterly winds is expected at KIPL this evening and during the overnight hours. At KBLH, a period of light southerly/southwesterly winds is expected this evening and during the overnight hours. Clear skies will persist. && .FIRE WEATHER... Strong high pressure will persist over the region through at least the weekend resulting in well above normal temperatures and continued dry conditions. Lower desert highs temperatures are likely to reach 10-13 degrees above normal starting today and through the weekend. MinRHs will continue to dip down to around 10% over the lower deserts to 15-20% over higher terrain areas through the rest of the week, while winds remain light generally following diurnal wind patterns. && .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 Sep 30 107 in 2010 109 in 2012 108 in 2020 Oct 1 107 in 2020 110 in 1980 110 in 1980 && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning from 10 AM Thursday to 8 PM MST Saturday for AZZ530-533-534. Excessive Heat Warning until 8 PM MST Sunday for AZZ537>544-546- 548>551-553>555-559. Excessive Heat Warning from 10 AM Friday to 8 PM MST Saturday for AZZ531-532-535-536. CA...Excessive Heat Warning from 10 AM Thursday to 8 PM PDT Saturday for CAZ569. Excessive Heat Warning from 10 AM Friday to 8 PM PDT Saturday for CAZ566-567-570. && $$ DISCUSSION...18/Kuhlman AVIATION...Berislavich FIRE WEATHER...Kuhlman CLIMATE...18