Sunrise 5:40 AM   Sunset 7:41 PM Moonrise 2:28 PM   Moonset 2:39 AM

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FXUS65 KPSR 172351 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 451 PM MST Fri May 17 2024

UPDATE
Updated Aviation Discussion.

SYNOPSIS
High pressure will strengthen over the region the next couple days resulting in many more lower desert communities exceeding 100 degrees. A dry weather disturbance will move north of the region early next week with temperatures retreating closer to the seasonal normal. Occasionally breezier conditions are likely during the afternoon and evenings early next week under mostly clear skies.

DISCUSSION
With Rex blocking situated across the central Pacific basin early this afternoon, downstream shortwave ridging has built into the SW Conus with H5 heights hovering around 582dm as the separate midlatitude and subtropical jet cores bifurcate the region. Into early next week, a portion of the cyclonic circulation comprising the base of the blocking pattern will eject eastward while phasing into the amplification of positively tilted, northern stream troughing. While the combination of forced ascent and moisture profiles should be insufficient for precipitation generation, ample height falls and jet energy crossing the forecast area will be capable of supporting enhanced afternoon/evening wind gusts.
Otherwise, some form of quasi-zonal flow will persist through the remainder of next week with H5 heights oscillating in a 572-578dm range yielding temperatures not terribly far from climatology.

Recent objective analysis indicates midlevel heights and temperatures increasing over the region with stronger anti-cyclonic subsident flow building over the CWA This pattern has resulted in modest warming over the Southwest, and early afternoon readings were already eclipsing the lower to middle 90s across lower desert communities. Model guidance spread remains very narrow suggesting excellent forecast confidence of temperatures remaining some 5F-10F above normal through tomorrow afternoon equating to areas of moderate HeatRisk. By the end of the weekend, the first vestiges of cyclonic flow and erosion of high pressure will enter the area bringing a brief, modest cooling trend along with a spell of strong, gusty winds early next week.

While some increase in wind speeds should be realized Saturday, the more notable winds with direct tangible impacts will arrive Sunday and Monday. An increasing gradient Sunday will be associated with the initial round of height falls and introduction of a subtropical jet core punching into the region. Afternoon/early evening gusts upwards of 20-30 mph may become common, especially over SE California aided by terrain features and a sundowner component. Further strengthening is anticipated Monday as the combination of shortwave energy, jet core, and tightened pressure gradient become maximized over the forecast area. Feel recent developmental changes in the mandatory NBM initialization have degraded wind forecasts at lower elevations, and have attempted to boost speeds to match the synoptic pattern and forecast BUFR sounding output. This would place much of the area near critical fire weather thresholds that would be concerning for any ongoing or new fire starts Monday afternoon. Otherwise, the remainder of the week should be characterized by quasi-zonal flow (really just swinging between broad troughing and flat ridging) yielding tranquil conditions with near normal temperatures and typical springtime afternoon gustiness.

AVIATION
Updated at 2351Z.

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

No major weather issues will exist through Saturday evening with only a FEW passing mid/high clouds at times. Wind behavior across the Phoenix metro will be similar to the past 24 hours, with afternoon/early evening winds gusting to around 20 kts at times. At the SE California terminals, W/SW winds gusting to around 25 kts will continue before tapering off this evening. Breezy afternoon winds will resume again tomorrow gusting to around 25 kts.

FIRE WEATHER
High pressure will hover over the region through the weekend with dry conditions and temperatures reaching much above normal. Only a disturbance moving north of the districts early next week will allow temperatures to cool closer to the seasonal normal. Throughout next week, minimum afternoon humidity levels will fall into the single digits at lower elevations and the teens across higher terrain areas. This will follow poor to fair overnight recovery of 20-40%.
Breezy afternoon/early evening conditions with gusts around 20 mph will be common, though somewhat stronger winds will occasionally be possible in far western districts. The greatest weather concern will occur Monday afternoon where frequent, widespread wind gusts closer to 30-35 mph may be common yielding near critical thresholds when combined with low RH and dry fine fuels.

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

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