Sunrise 5:47 AM   Sunset 7:29 PM Moonrise 4:44 AM   Moonset 6:14 PM

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FXUS65 KPSR 060551 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 1050 PM MST Sun May 5 2024

UPDATE
Updated Aviation

SYNOPSIS
A dry weather system currently moving just north of the region will promote breezy to windy conditions along with slightly cooler than normal temperatures today. The weather pattern heading into the upcoming week will feature seasonably dry conditions and temperatures gradually rebounding to near normal range as well as breezy conditions each afternoon.

DISCUSSION
Latest water vapor satellite imagery depicts a potent upper-level low pressure system moving across the northern Great Basin with its base extending into the Desert Southwest. This is leading to a tightening of the pressure gradient and thus enhanced winds through this afternoon into the early evening hours. Peak wind gusts upwards of 30 to 35 mph are likely across most of the lower desert communities, with localized gusts upwards of 40-45 mph across portions of southeast CA, especially Imperial County, as well as the higher terrain areas to the north and east of Phoenix. The strong winds will result in some elevated fire weather concerns as well as areas of blowing dust, especially across the western deserts. In addition to the gusty winds, high temperatures this afternoon will be noticeably cooler with highs topping out in the mid 70s to low 80s across the western deserts to mid to upper 80s across the south- central AZ lower deserts, including the Phoenix metro area.

The upper-level low pressure system by Monday will have quickly moved east-northeastward into the Plains states. Winds will be noticeably lighter compared to today and temperatures will be noticeably warmer across the western deserts with highs rebounding in the middle 80s while remaining steady state across the south- central AZ lower deserts in the mid to upper 80s. The weather pattern heading through the middle of the week will feature a broad trough extending from the Plains states through the Pacific northwest with the southern fringes clipping the Desert Southwest.
Under this pattern, our region will be situated in mostly zonal flow with temperatures only gradually rising into the lower 90s while at the same time the flow aloft will be strong enough to produce breezy conditions with afternoon and early evening gusts in excess of 20-25 mph.

Both the deterministic and ensemble model suite by the latter half of the week are indicating that as an upper-level ridge begins to build near the Pacific northwest coast, a piece of energy from the aforementioned trough is expected to break off and retrograde close to our region heading into Thursday and Friday. Not much in the way of sensible weather impacts are expected from this feature other than continuing the breezy conditions as well keep the upper-level heights suppressed to maintain temperatures from rising even further. Eventually, as the upper-level ridge axis builds further east and displaces the shortwave trough eastward sometime next weekend, heights aloft will rise accordingly. This will lead to temperatures rising further, with latest NBM guidance showing widespread highs in the upper 90s across the lower deserts with a 20- 40% of approaching 100 degrees.

AVIATION
Updated at 0550Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Westerly winds prevailing well into the overnight hours will be the greatest weather issue under clear skies. Forecast confidence is very good that winds will continue to weaken with a west component persisting much later into the overnight than is typical. Some locations (such as KPHX) potentially may never truly switch to the traditional morning easterly wind forcing runway configurations to remain the same throughout the period. Regardless, widespread westerly winds will prevail over the entire metro again by late morning with only limited afternoon gusts.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather concerns should exist through Monday evening under clear skies. Any lingering wind gusts should quickly weaken overnight with trends in directions veering to a more N/NW direction. Wind speeds should weaken even further during the day with moderate confidence of becoming more variable in direction by the afternoon.

FIRE WEATHER
A weather system moving just to the north of the region today will bring breezy to windy conditions areawide. Wind gusts of 25-35 mph are likely in many areas this afternoon with upwards of 40-45 mph possible across portions of southeast California and over the high terrain north and east of Phoenix. The strong winds and dry conditions with humidities as low as 20% today could lead to elevated fire weather conditions. Lighter winds are expected by Monday with MinRHs lowering to around 10%, with overnight recoveries of 20-50%. Weak high pressure will then remain over the region through much of the coming week as temperatures return to slightly above normal by late week. Seasonably dry conditions are expected this week with MinRHs dropping to around 10% each day starting Monday. Winds this week will be fairly light most days, except for Tuesday and Wednesday when winds will be more elevated with afternoon gusts between 20-30 mph in some areas.

PSR WATCHES/WARNINGS/ADVISORIES
AZ...None.
CA...None.

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