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FXUS65 KPSR 101200 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 500 AM MST Sun Dec 10 2023

UPDATE
Updated 12Z Aviation Discussion.

SYNOPSIS
High pressure will build back into the region early this week resulting in a slight rebound in temperatures. During the middle of the week, a weather disturbance will slide into the area halting any additional warming, but offering little to no chance of precipitation. The warming trend may resume late in the week as widespread dry conditions persist.

DISCUSSION
Deep troughing was progressing into the eastern Conus early this morning as high pressure builds into the West with the overall western hemisphere flow pattern entering an amplification phase.
Strong surface high pressure remains entrenched across the central/southern Rockies with the thermal gradient aiding in another round of nocturnally enhanced winds across higher terrain and foothill locations. With a drier airmass in place (surface dewpoints largely in the single digits), decoupled sheltered valley have an optimal radiational cooling setup. However, locations where winds persist have not cooled substantially leading to a wide range of temperatures in close proximity. A Freeze Warning continues for the San Carlos area this morning, though many other of the more isolated cold susceptible locations will likely close in on freezing temperatures by sunrise.

Midlevel H5 height rises will become rather pronounced over the next 36 hours with readings potentially reaching a 582-585dm range. As a result, temperatures will warm a few degrees though still hover not terribly far above the climatological normal. All model suites continue to depict further pattern amplification through the week with broad ridging spanning the northern Conus while weak shortwave energy descends and cuts off over the Southwest during the middle of the week. While there remains uncertainty regarding the depth and exact position of this cutoff feature, it will likely inhibit further height rises leading to a temporary cessation of the warming trend. Given the overland trajectory of the originating PV anomaly entering an already dry airmass, precipitation chances across the CWA remain limited, at best. However, there has been recent signals in operational models that the cold core intercepting a backdoor moisture push over east central AZ may be sufficient to squeeze out a few showers; and a modest bump in NBM POPs has been noted in recent forecast iterations.

While forecast confidence late in the week remains somewhat low due to upstream blocking evolution, there has been convergence on a similar outcome from the majority of ensemble membership. The aforementioned cutoff low should eject into the plains and become absorbed into the mean trough position off the East Coast by the weekend. Concurrently, a deep negative PV anomaly should become disassociated from the northern jet west of the California coast forcing strong ridging to intensify over the SW Conus. Given the pattern, it would not be outlandish if H5 heights exceeded 585dm for a period over the weekend with temperatures increasing 5F-10F above normal. There are a handful of ensemble members that attempt to push shortwave energy and an associated frontal boundary onshore late in the weekend, however with the higher amplitude blocking type pattern in place, a slower progression of features is preferred and this minority solution was discounted.

AVIATION
Updated at 1200Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected through the forecast period. Light and variable winds will continue at KPHX, KIWA, and KSDL before developing an easterly component between 14-19Z. At KDVT current NE'rly winds will become more SE'ly late this morning. The typical afternoon W shift is not anticipated to occur today. Wind speeds will generally be aob 7 kt aside from a period of some elevated speeds with periodic gusts of 10-15 kt possible from 17-19Z today. Skies will remain clear until FEW-SCT high clouds move into the region this evening.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation concerns are expected through the forecast period.
Wind speeds will be aob 9 kt at both terminals through the forecast period. At KIPL, current westerly winds will become northwesterly late this morning before switching back to the west this evening. At KBLH, current northwesterly winds will become northerly late this morning before switching back to the NW this evening. Skies will remain mostly clear until high clouds move in this evening.

FIRE WEATHER
Temperatures will warm a few degrees through the first half of the week as high pressure generally settles over the region. Another round of gusty northeast winds will impact ridge tops and terrain gaps of eastern districts through this afternoon resulting in a locally elevated fire danger. Wind speeds across the entire region should decrease quickly thereafter. Minimum afternoon humidity levels will fall primarily in a 10-15% range the next couple days following poor to fair overnight recovery of 15-35%. A weak weather system descending into the area during the middle of the week will bring a modest increase in moisture with afternoon humidity levels improving closer to a 15-25% range. A few showers may affect far eastern Gila County with this system, however wetting rainfall should not be expected while the remainder of the area stays dry.

PSR WATCHES/WARNINGS/ADVISORIES
AZ...Freeze Warning until 9 AM MST this morning for AZZ560.

CA...None.

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