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FXUS65 KPSR 082026 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 126 PM MST Fri Dec 8 2023

SYNOPSIS
Temperatures will continue their downtrend through Saturday as a trough and subsequent cold front push their way across the region.
Breezy to locally windy conditions can be expected late tonight through Saturday across the high terrain of SE California and south-central Arizona. High pressure looks to build over the western U.S. by the end of the weekend, leading to a slight rebound in regional temperatures.

DISCUSSION
Current analysis reveals broad, low amplitude troughing draped across the western CONUS with a few embedded shortwaves helping to bring rain and snow to portions of the Intermountain West. Over the Desert Southwest, we will continue to be dry as most of the energy with these systems will stay north of our CWA. However decreasing heights due to the troughs' proximity will help temperatures continue their cooling trend that we have seen for the past few days. Highs across the lower deserts for this afternoon will mainly range between the upper 60s and low 70s.

Upstream ridging will likely slide over the western CONUS, promoting surface pressure rises over the Desert Southwest as we head into Saturday. These pressure rises will help push a cold front down across the region early late tonight/early Saturday morning, providing a reinforcing push of relatively cooler air across our area. Temperatures for Saturday will be right around climatological normals, with morning lows ranging form the upper 30s to mid-40s and afternoon highs in the mid to upper 60s for lower desert communities. The coldest post-frontal temperatures will likely occur Saturday night into Sunday morning. Isolated areas, mainly sheltered valleys and high-terrain locations of southern Gila County and parts of rural La Paz County may see their first freeze of the year. However, due to the expectation of only a few isolated locations flirting with freezing temperatures, freeze products are unlikely to be issued, barring any significant changes in guidance over the next day or so.

The aforementioned cold front will also aid in tightening up our regional pressure gradient, providing portions of our CWA with breezy to locally windy conditions late tonight through Saturday.
The enhanced terrain of SE California will be the focus of the strongest winds, with the NBM indicating an 80-90% chance of seeing advisory level gusts (>=40 mph) through about noon local time Saturday. Post-frontal breeziness will also exist over the lower Colorado River Valley and the Arizona high terrain. Winds over these locations, however, will likely remain below advisory levels with peak gusts upwards of 30-35 mph.

Model clusters remain in excellent agreement regarding a ridging pattern becoming established over the western CONUS by the end of this weekend. Heights aloft as a result of this pattern change will be on the rise, likely leading to a slight rebound in our temperatures on Sunday. There is also increasing confidence surrounding the development of a shortwave trough over the Desert Southwest early next week, but not all models agree on how amplified this feature may become, with some indicating the development of a cutoff-low. How much this feature develops will determine its' pace of progression, with a closed low favoring a slower-moving system compared to an amplified open wave.
Regardless, the development of this trough would inhibit further regional height rises, helping to keep temperatures steady through much of next week with afternoon highs slightly above seasonal normals. Given the anticipated inland trajectory of this system and limited moisture expected to be available, rainfall chances will be minimal with dry conditions favored through next week.



AVIATION
Updated at 1730Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: VFR conditions with mostly clear skies will prevail through the forecast period. Winds will follow typical diurnal tenancies and remain at or below 6 kts. Winds are expected to switch out of the WSW by 19Z-20Z. This will be followed by a N-NE shift later tonight. However, there is less confidence in an established direction at KPHX due to a weak sfc gradient and therefore winds will become moreso light and variable after sunset. By tomorrow morning, winds will become northeasterly at all terminals.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation concerns are expected through the TAF period with mostly clear skies. At KIPL, northwesterly winds will carry through this afternoon and into tonight with speeds generally remaining around 5 kts or less. At KBLH, northerly winds will become established this afternoon with speeds ramping up through this evening to around 11-15 kts. Elevated northerly flow will continue through the overnight period.

FIRE WEATHER
With temperatures hovering near normal, a period of gusty northeast winds will affect the region the next several days. The strongest winds should funnel down the lower Colorado River valley beginning tonight, as well as eventually impacting ridge tops and gaps across eastern districts through the weekend. This will result in periods of an elevated fire danger with dry fuels and low humidity levels.
In fact, minimum afternoon humidity levels will fall primarily in the teens following only poor to fair overnight recovery of 20-40%.
Lighter winds will return by the middle of next week with the potential for some modest moisture increase.

PSR WATCHES/WARNINGS/ADVISORIES
AZ...None.
CA...Wind Advisory from 9 PM this evening to noon PST Saturday for CAZ564-565-568.

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