Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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510 FXUS65 KPSR 061134 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 434 AM MST Sun Oct 6 2024 .UPDATE...Updated 12z Aviation Discussion. && .SYNOPSIS... Lower desert high temperatures near 110 degrees are expected for at least two more days before finally trending slowly downward. Unfortunately high temperatures will still be near daily records through most of the week for many locations with minimal relief from a midweek disturbance. Temperatures are forecast to cool more, but still remain above normal, as another disturbance moves in heading into next weekend. && .DISCUSSION... Only two more days of lower desert high temperatures near the 110F mark are expected before temperatures finally begin a slow downward turn across the region. Despite the downward turn, afternoon high temperatures are still forecast to be near or breaking daily records - which are in the lower 100s - through the coming workweek as highs reach around 10 degrees above normal (see CLIMATE section below). Normal highs this time of year are in the lower 90s. Abnormally strong high pressure and fairly stagnant dry air continues to drive the 110 degree heat. The H5 height field and 850mb temperatures lower slightly by the middle of the week as a very weak trough pushes in from the west and draws a little bit of moisture and clouds into the Desert Southwest. The NBM adds very low PoPs (<10%) to the region Tuesday and Wednesday, but any rain shower will be most favorable over higher terrain areas and likely low impact. The clouds could help block the sun at times and temporarily alleviate afternoon heat. However, the clouds and slight uptick in moisture do not look like they will be enough to keep some areas, like Phoenix, from reaching Major HeatRisk again on Tuesday. For this reason the Excessive Heat Warning has been extended through Tuesday now just for the Phoenix area. By the end of the week and into the weekend global models remain consistent in showing a trough moving into the Western CONUS from the Eastern Pacific, but uncertainty increases considerably in what this trough will do once pushing inland. The majority of ensemble members at least have this trough influence the weather conditions in the Desert Southwest, but they also keep the trough pretty weak. Looking at the latest ensemble clustering the biggest variance in the large-scale synoptic pattern for the Western CONUS appears tied to the uncertainty in amplification of upstream PacNW ridging and Eastern Pacific troffing behind the trough moving inland at this week. Ridging in the Northwest would open the door for the trough late this week to close off somewhere in the Desert Southwest, which is being hinted at by individual global models, including both the latest GFS and ECMWF deterministic runs. While this sounds like a nice change and may bring rain and cooler temperatures to the region this is still a week away and reality may still be temperatures well above normal and little to no rainfall for much of the region. Time will tell. && .AVIATION...Updated at 1135Z. South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns are anticipated through the TAF period under mostly clear skies. Overall wind pattern will continue to exhibit the typical diurnal tendencies with light speeds mostly aob 7 kts. There will likely be extended periods of very light/calm and variable winds, especially during the periods of diurnal transitions. && .FIRE WEATHER... Very dry and extreme heat conditions will continue for many areas through Tuesday, with lower desert highs ranging between 104-112 each afternoon. MinRH values in the afternoons in the 5-10% range will be common through at least Tuesday, while MaxRH readings are expected to be between 20-30%, with locally higher values in Yuma and Imperial Counties. The driest conditions are expected today through Monday afternoon, with RH values under 25% in most areas for the next 36-48 hrs. An increase in winds above the surface during the overnight hours, this morning and again tonight/Monday morning, may lead to very localized elevated fire weather conditions in South-Central AZ. Easterly winds during the overnight hours on and near ridgetops will be capable of reaching 25-35 mph at times, mostly in the mountains east of Phoenix. There will be a very slight increase in moisture beginning midweek that may keep MinRH values from falling into the single digits, but most areas will still see 10-20% readings in the afternoon through the end of this week. There will also be potential for some regional rain showers with the moisture increase, but at this time the chances are very low (5% or less) across the lower deserts and CWR is near zero. Winds, beyond Monday, will follow familiar diurnal trends, with occasional afternoon gusts near 15-25 mph. && .CLIMATE... Record highs through Friday: Date Phoenix Yuma El Centro ---- ------- ---- --------- Oct 6 105 in 1917 108 in 1980 106 in 1964 Oct 7 104 in 1991 108 in 1987 105 in 1991 Oct 8 104 in 1987 107 in 1996 106 in 1996 Oct 9 103 in 1996 106 in 1996 104 in 1996 Oct 10 105 in 1991 107 in 1991 105 in 1996 Oct 11 102 in 1991 107 in 1950 106 in 1995 && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Monday for AZZ530>536-538- 539-553>555-559. Excessive Heat Warning until 8 PM MST Tuesday for AZZ537-540>544- 546-548>551. CA...Excessive Heat Warning until 8 PM PDT Monday for CAZ562-566-567- 569-570. && $$ DISCUSSION...Benedict AVIATION...Whittock/Lojero FIRE WEATHER...Benedict CLIMATE...18