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FXUS65 KPSR 111709 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 1009 AM MST Mon Dec 11 2023

UPDATE
Updated Aviation Discussion.

SYNOPSIS
Warming temperatures to start the workweek with a brief cool down expected by midweek as a low pressure system moves through Arizona.
While dry conditions are expected for the majority of the area through at least next weekend, the previously mentioned low pressure system will bring a slight chance of showers to the higher terrain in southern Gila County late Wednesday into early Thursday morning.
Once this low pressure system passes through high pressure will build back in over the region leading to a warming trend for the end of the workweek and the weekend.

DISCUSSION
Streamline analysis this morning shows quasi-zonal flow over much of western CONUS with a trough beginning to dig over northern California. Upper-level WV imagery reveals a plume of Pacific moisture moving over southwestern CONUS. This plume of Pacific moisture will increase upper-level moisture causing considerable cloudiness building in across Arizona throughout the day today. FEW- SCT high clouds this morning will result in another chilly morning with lows dipping into the low-to-mid 40s across the much of the lower deserts and mid-to-upper 30s across the higher terrain and rural deserts. Increasing cloud cover this afternoon will result in suppressed afternoon high temperatures with the lower deserts seeing afternoon highs in the upper 60s and low 70s and the higher terrain topping out in the mid 60s.

Increased cloud cover overnight tonight will lead to warmer morning lows on Tuesday. Tuesday morning lows will be in the mid-to-upper 40s and low 50s for much of the lower deserts and in the low 40s for the higher terrain and rural deserts. Cloud cover will decrease across the region on Tuesday as the trough digs into southern CA and western Arizona pushing the plume of Pacific moisture and associated clouds to the east of our region. Clouds exiting the region on Tuesday will allow for slightly warmer afternoon temperatures on Tuesday than today.

Deterministic and ensemble models show the trough continuing to deepen and becoming a cutoff low in northern Arizona early Wednesday morning. However, there does still remain some discrepancy on the exact strength and position of this cutoff low. This cutoff low will bring decreased heights aloft on Wednesday which will allow for a slight cool down. Afternoon high temperatures will be in the upper 60s and low 70s across the lower deserts and in the low-to-mid 60s across the higher terrain. The cutoff low overhead on Wednesday will result in breezy conditions across southeast California and the Colorado river valley Wednesday afternoon, with gusts of 20-25 kt possible. Most of the region will remain dry as this system passes through due to the lack of moisture as PWATs will range from 0.2- 0.4” across the CWA. The highest moisture will be in place over the higher terrain in southern Gila County. While chances are low, around 20% or less, there may be enough lift to squeeze out a few sprinkles or light showers across the high terrain in southern Gila County late Wednesday night into early Thursday morning.

The cutoff low will quickly exit the region to the east with a ridge moving in on Thursday. The ridge building in will allow for a slight increase in temperatures on Thursday. This ridge will continue to build and amplify over the region heading into the weekend. This high amplitude ridge will result in temperatures well above normal for the end of the workweek and for the weekend. Daily afternoon high temperatures are currently forecasted to be 8-12 degrees above normal this weekend.

AVIATION
Updated at 1708Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT; and Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns are expected through the TAF period under occasional periods of thicker high cirrus. Confidence is very good that light east winds will be common most of the period around the Phoenix metro with only a brief window around sunset where directions shift to westerly. N/NW winds will be preferred at KBLH and WNW at KIPL in SE California with extended periods of nearly calm conditions likely.

FIRE WEATHER
With high pressure overhead, temperatures will warm slightly through Tuesday. Wind speeds will be light through Wednesday morning and generally be under 10 mph. Relative humidity values will range from 10-15% this afternoon and Tuesday afternoon. Overnight recovery will be poor to fair and range from 15-35%. A low pressure will move through Arizona on Wednesday and exit on Thursday. This system will cause a slight increase in moisture with afternoon RH values ranging from 15-25% on Wednesday and Thursday. This system will also bring elevated wind speeds of 20-25 mph to SE CA and the CO river valley Wednesday afternoon. While most of area will remain dry, a few showers will be possible in the high terrain in southern Gila County Wednesday night into Thursday morning. Wetting rainfall not expected with this system.

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

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