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FXUS65 KPSR 291131 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 431 AM MST Wed Nov 29 2023

Update
Updated Aviation

SYNOPSIS
A weather system will move into the region from the west later today bringing decent chances for light precipitation over the Arizona higher terrain and the beginning of a cool down. A second fast moving system will then quickly follow behind late Thursday into the first part of Friday bringing better widespread precipitation chances focused across south-central and eastern Arizona. Below normal temperatures will also settle in across the region starting Thursday, lasting through the weekend. High pressure and warmer conditions are expected to return starting early next week.

DISCUSSION
The upper level ridge that brought a couple days of above normal temperatures has exited to the east with a trough of low pressure now moving into California from the eastern Pacific. For the first part of today, there will be little change in sensible weather conditions with some high clouds moving through and highs reaching into the lower 70s, or right around normal. As the low continues to move southeastward across California later today, winds will become quite breezy across portions of southeast California with gusts above 30 mph possible this evening across the western half of Imperial County.

By later this evening, the fast moving neutrally tilted trough is expected dig across our region with the main area of PV tracking across southern Arizona. Moisture will be fairly limited across our area as the system passes through with low level mixing ratios at around 0.5 g/kg, but there should still be adequate forced ascent for some scattered showers to develop over the higher terrain east of Phoenix late this evening through just before sunrise. The limited moisture and brief window of shower potential should only result in rainfall amounts generally 0.1" or less across Gila County tonight.

As today's shortwave exits into New Mexico tomorrow morning, a second shortwave will quickly follow behind reaching southern California Thursday afternoon and over Arizona by the evening hours. Additional mid and upper level moisture is likely to be added to our area just ahead of this next disturbance as forecast PWATs increase to 0.6-0.7" (150-175% of normal), while low level mixing ratios stay between 5-6 g/kg. System dynamics with the shortwave on Thursday don't look impressive at all, but models are fairly optimistic with rain chances across south-central and eastern Arizona likely due to modest 20-25kts of southwesterly upslope flow somewhat coinciding with the passing jet streak across the region. Both the latest 00Z GEFS and EPS show better potential for precip Thursday night compared to previous runs allowing QPF to be bumped up to 0.2-0.35" across the Phoenix area and to 0.4-0.6" over much of the higher terrain north and east of Phoenix. Any shower activity is likely to wind down across the Phoenix area by mid morning Friday and then by mid afternoon across higher terrain areas as the trough lifts to the northeast.
Forecast snow levels of around 6000 feet through the event will likely keep the precip all rain for the majority of our area, aside from the highest peaks in southern Gila County.

Temperatures will fall further starting Thursday with highs only reaching into the mid to upper 60s across the lower deserts.
Highs Friday should even be a couple degrees cooler with most areas only topping out between 62-65 degrees, or around 5 degrees below normals. These below normal temperatures will persist into the weekend as ensembles show our region staying under broad troughing aloft, keeping the cool air mass in place. Overnight lows will fall further over the weekend as we dry out and winds become light. The coldest overnight lows are currently forecast for Sunday morning with lower desert readings mostly between the mid 30s to lower 40s. Some of the more typical coldest lower desert rural areas and even Globe may see their first freeze or near freeze of the season Sunday morning.

The below normal temperatures won't last long though as long range guidance fully supports strong ridging building across the eastern Pacific on Sunday before moving across the Western U.S. during the first half of next week. This will lead a gradual warm up over our region starting Sunday with above normal temperatures likely returning as early as Monday. NBM temperature guidance also shows highs potentially reaching into the mid to upper 70s again by the middle of next week as the ridge moves overhead.

AVIATION
Updated at 1130Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns are expected during the TAF period.
Winds will follow familiar diurnal tendencies with speeds generally remaining below 10 knots. Winds may take longer than usual to shift back to the E tonight which will allow for a brief period of light S'rly winds. FEW lower level clouds with bases around 8 kft will continue to filter in throughout the period with SCT-BKN mid and high clouds moving in by late morning.

Southeast California/Southwest Arizona including KIPL and KBLH: Breezy conditions at IPL will be the main aviation concern during the forecast period. Winds there will be out of the W through tonight, with gusts near 25 kts developing by late this afternoon before eventually calming by late evening. At BLH, VRB winds will become established out of the SW by this afternoon. SCT-BKN clouds this morning will eventually clear out by this afternoon with only a FEW mid and upper level clouds remaining.

FIRE WEATHER
A couple of weak weather disturbances are expected to affect the region through Friday with the first one moving through later today and tonight and the second late Thursday into Friday. As a result, moisture will increase over the next couple days pushing MinRHs to above 35% on Thursday and Friday. Rain potential later today will be confined to the Arizona high country, while the second system is likely to bring good chances for wetting rains over much of southern and central Arizona. Expect some breezy conditions mainly across the western districts later today and again areawide on Thursday. For the weekend into the first part of next week, high pressure and drying conditions will take over leading to a return of above normal temperatures by around Monday and MinRHs dropping to between 20-30% by Sunday or Monday.

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

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