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FXUS65 KPSR 291120 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 420 AM MST Mon Apr 29 2024

UPDATE
Updated Aviation

SYNOPSIS
Warmer temperatures are anticipated over the next several days with highs rising into the low to mid 90s across the lower deserts. An upper level trough will pass through the Intermountain West mid-week resulting in breezy conditions across southcentral AZ and southeast CA. Otherwise, dry conditions will prevail across the forecast area through at least this weekend.

DISCUSSION
Latest mid-lvl wv imagery and 500 mb streamline analysis reveals broad longwave troughing over the central U.S. with dry NW flow present over AZ and southeast CA. As we head through today, upper level flow will transition to quasi-zonal as another trough enters the Pacific NW. As this occurs, we will see 500 mb hghts rise to around 575-577 dam over the forecast area by this afternoon.
Consequently, mid-level temperatures will increase by a few degrees compared to yesterday which will result in highs rising to above normal levels. Expect temperatures to top out into the upper 80s to lower 90s across the desert communities under clear skies and light winds. Dry, tranquil conditions will carry into tonight with lows falling to the upper 50s to lower 60s. On Tuesday, mid-lvl hghts/thicknesses will increase further with 850 mb temperatures rising to 18-21 deg C. This will promote sfc highs in the low to mid 90s or around 3-6 degrees above average.

On Wednesday, a shortwave trough will swing through the Intermountain West, resulting in the tightening of the 700-500 mb hght gradient over our forecast region. This will lead to increased breeziness with gusts up around 20-25 mph across much of the area. A decrease in overall 500 hghts will result in a slight cool down with highs closer to normal Wednesday afternoon. The afomentioned shortwave trough will continue to progress through the 4-Corners region on Thursday, sending a backdoor front into the Colorado River Valley where gusty northerly winds will be possible during the morning hrs. This front will be quite weak however and will result in no sensible change to the temperatures with highs still expected to reach the lower 90s by Thursday afternoon.

As we head into this weekend there is still a fair amount of spread between global ensembles regarding the upper level pattern. The GEFS is showing a fairly robust trough moving onto the CA coast by Sunday into Monday whereas the EPS is indicating that troughing will be much more subdued and confined to the Pacific NW. The deterministic NBM indicates highs continuing in the low to mid 90s through this weekend, though a larger temperature spread is seen in the interquartile range due to the aforementioned model uncertainties.
Despite the uncertainty in temperatures, ensembles and deterministic models do agree that dry conditions are favored to persist through this weekend and into early next week and thus PoPs remain nil.

AVIATION
Updated at 1120Z.

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

Expect VFR conditions for all terminals. No major weather issues anticipated through Monday Morning under clear skies. Timing of the usual diurnal wind shifts will be typical for this time of year while any enhanced gusts remains minimal or absent. Look for extended periods of nearly calm conditions.

FIRE WEATHER
Warm and dry conditions will persist this week and into this weekend with high temperatures around 3-5 degrees above normal each day.
Winds will be light and follow typical upslope/downvalley patterns today and Tuesday before increased breeziness arrives Wednesday with gusts reaching the 20-25 mph range across much of the area. Windy conditions will also be possible across the western districts on Thursday as a dry cold front passes through the Colorado River Valley. Minimum relative humidity values will range from 10-15% today. However, it will become noticeably drier across the lower deserts by mid-week with sub 10% RH values possible in some locations. Moisture recovery will range from poor to fair each night, or around 25-50%.

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

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