Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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941 FXUS65 KPSR 120839 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 139 AM MST Wed Jun 12 2024 .SYNOPSIS... Very hot and dry conditions will continue over the next couple days with the Excessive Heat Warning in effect through Thursday across much of south-central Arizona and high temperatures between 107 and 112 degrees across the lower deserts. A dry weather system will then move across the area later Thursday into early Friday potentially leading to some light showers across higher terrain areas, mostly cloudy skies, and breezy conditions. The coming weekend should see temperatures around 110 degrees across the lower deserts before temperatures cool back to around normal early next week. && .DISCUSSION... The sub-tropical ridge, which extends north to south from the Great Basin into Mexico, is bringing H5 heights as high as 592dm across the eastern half of Arizona. Lower heights down to around 588dm are seen across the western deserts through southern California as it remains in closer proximity to a cut-off low that has been nearly stationary west of Baja. For today and Thursday, this set-up will again bring very hot temperatures across the majority of the area with highs between 106-110 degrees across southeast California to 108-112 degrees across the south-central Arizona lower deserts. An Excessive Heat Warning remains in effect through Thursday for Maricopa, Pinal, and portions of Gila County as these temperatures represent a Major HeatRisk for portions of the counties. During the daytime hours Thursday, guidance shows the cut-off low beginning to track northeastward closer to southern California before moving through southern California into western Arizona Thursday night. Southerly flow is forecast to increase on Thursday into Arizona leading to some increased moisture advection in the mid to upper levels. Model soundings show this moisture layer down to around 13-15K feet by Thursday afternoon which should be enough to lead to some high-based shower activity across southern and central Arizona Thursday afternoon and evening. Given the very dry air below the cloud bases, the most the lower deserts can expect is some sprinkles, but some very light measurable rainfall with PoPs of 10-20% will be possible over the Arizona higher terrain. Also can`t completely rule out some localized gusty winds mainly across western Arizona due to these possible virga showers. The cut-off low will continue to weaken and move into northern Arizona on Friday while the rebuilding sub-tropical ridge moves in behind from the southwest. Forecast temperatures are a few degrees cooler across Arizona on Friday due to the low, but the building heights across the western deserts should lead to highs around 110 degrees across southeast California and far southwest Arizona. As H5 heights once again rise to between 590-592dm Friday night into Saturday, temperatures will heat up further on Saturday as NBM forecast highs are mostly between 109-114 degrees. These temperatures will once again flirt with Major HeatRisk in some areas. Starting Sunday, ensemble guidance heavily favors a fairly strong upper level trough digging across the Northwest U.S. with the southern fringes of the troughing extending as far south as the Desert Southwest. This will begin to lower heights across our region, but the cooling will be subtle on Sunday before becoming much more noticeable by Monday. The core of the trough is expected to miss us to the north as it likely moves through the Great Basin on Tuesday, but it is expected to bring some modest relief from these very hot temperatures. NBM forecast temperatures lower back to around normal for the first half of next week with lower desert highs mostly between 102-107 degrees. && .AVIATION...Updated at 0535Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT; VFR conditions at all terminals under some passing high clouds can be expected through the TAF period. Winds will continue to exhibit diurnal tendencies with speeds generally remaining aob 10 kts, although some occasional afternoon/early evening gusts into the mid-teens cannot be ruled out. Winds will again have tendencies to have variability characteristics in direction and speeds during the transition periods, especially at KPHX. Southeast California/Southwest Arizona including KIPL and KBLH: VFR conditions at both terminals under some passing high clouds can be expected through the TAF period. At KIPL, winds will be out of the westerly direction into the overnight hours before light winds settle in into the morning hours. At KBLH, winds will generally be out of the south to southwest. Wind speeds will remain aob 10 kts through tomorrow morning, with afternoon winds generally around 10 kts, but cannot rule out sustains reaching up to 15 kts, with occasional gusts above 20 kts at both terminals in the later portions of the afternoon and into the evening hours tomorrow. && .FIRE WEATHER... Well-above-normal temperatures along with dry conditions will prevail over the next couple days. Lower desert high temperatures will top out between 107-112 degrees through Thursday. Winds will continue to favor diurnal tendencies with occasional afternoon gusts up to 20 mph today and to around 25 mph on Thursday when some high based virga shower activity could bring a brief enhancement of the winds. MinRH values will range between 5-10%, while poor overnight recoveries can be expected with MaxRHs only reaching towards 15-35%. Above normal temperatures will continue through the upcoming weekend, while winds increase further with afternoon gusts of 20-30 mph likely. The combination of the increased winds and continued low RHs will create even higher fire danger across the area this weekend. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Thursday for AZZ534- 537>555-559-560-562. CA...None. && $$ DISCUSSION...Kuhlman AVIATION...Young/95 FIRE WEATHER...Kuhlman