Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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986 FXUS65 KPSR 251705 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1005 AM MST Sat May 25 2024 .UPDATE... 18Z Aviation Discussion. && .SYNOPSIS... Widespread breezy conditions and below normal high temperatures can be anticipated this afternoon as a weak area of low pressure moves over the region. Daily highs are forecast to increase starting tomorrow, with a ridge of high pressure building over the Desert Southwest early next week. Triple digit highs return across much of the lower deserts by Memorial Day and are expected to persist through the middle of next week. && .DISCUSSION... The axis of a shortwave trough is moving onshore along the Southern California Coast early this morning. West southwest winds aloft have increased ahead of this trough (currently 30-35 kt down to ~650 mb as observed in ACARS soundings at Sky Harbor) and are expected to peak this morning before daytime heating can mix down this higher momentum air to the surface. As such, winds will increase earlier in the day today than they did yesterday, and peak gust values around 20-25 mph are forecast over much of the lower deserts this afternoon. Peak gusts may be closer to 25-35 mph across portions of Imperial County late this afternoon and early this evening. The South-Central AZ high terrain east of Phoenix will be more breezy than the lower deserts, with HREF probabilities of 30+ mph gusts ranging between 10-40%. HREF probabilities for gusts to 35+ mph drops off significantly to near zero in these locations, though some isolated gusts to 35 mph are possible. As a result, locally elevated fire weather conditions will exist along the South-Central AZ high terrain east of Phoenix this afternoon. Aside from widespread breeziness, the trough passing over the region today will bring cooler temperatures. Highs this afternoon will range from the upper 80s to lower 90s across the lower deserts - values which fall between 5-10 degrees below normal for the date. These below normal temperatures will be short lived. In the wake of the trough, temperatures are expected to rebound to near normal Sunday and continue increasing through the middle of next week as a ridge of high pressure builds over the western CONUS. Triple digit highs are likely (>70% chance) in Phoenix by Memorial day, with Tuesday shaping up to be the hottest day this week. Locally moderate HeatRisk will accompany the higher temperatures this upcoming week - as early as Monday in Southeastern California and Tuesday in the Phoenix Metro Area. Though global ensembles are in excellent agreement on the ridging pattern over the western CONUS through the middle of next week, solutions begin to diverge late next week. By the Thursday-Friday timeframe, disagreement exists over the evolution of a troughing feature over the Pacific Northwest. Recent GFS model runs show a trough moving onshore late Wednesday into Thursday, remaining far to the north and potentially sending some transient disturbances over the Desert Southwest along its base by Friday. This solution would be consistent with the deterministic NBM temperatures decreasing to near or slightly above 100 degrees late next week. The uncertainty in the upper air pattern late next week is reflected in the NBM temperature spread, with inner quartile values ranging from 100-105 degrees for Phoenix on Thursday and Friday. Dry conditions with near- zero rain chances can be expected with more certainty through the end of the month. && .AVIATION...Updated at 1705Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Breezy conditions will be the main aviation concern during the TAF period. Winds will follow familiar diurnal tendencies with afternoon gusts between 20-25 kts before speeds start to diminish after sunset. Clear skies can be expected through Sunday morning. Southeast California/Southwest Arizona including KIPL and KBLH: Breezy conditions will be the main aviation concern during the TAF period. Winds at IPL will remain out of the W through Sunday morning, with gusts this afternoon and evening around 25 kts, with occasional higher gusts. At BLH, VRB winds will eventually emanate out of the SW and gust near 25 kts this evening. Speeds at both terminals will begin to diminish after sundown. Clear skies will prevail through the forecast window. && .FIRE WEATHER... Locally elevated fire weather conditions will exist today, particularly over the high terrain of the eastern districts, as a weak system helps to generate widespread breezy conditions. Gusts over the high terrain of the eastern districts will peak between 25-30 mph, with isolated gusts potentially up to 35 mph. Gusts will peak mostly between 20-25 mph this afternoon elsewhere across the lower deserts. MinRH values will range between 10-20% today and locally higher in the high terrain, and will drop to 10-15% tomorrow. Overnight recoveries will be fair tonight at around 30- 50% and drop to 25-40% Sunday night. Hot and dry conditions will persist after today, with generally lighter wind speeds and typical afternoon breeziness each day. Daily highs will reach the century mark in many lower desert locations by Monday and values generally top out between 100-105 through the middle of next week. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Whittock AVIATION...RW FIRE WEATHER...Whittock