textproduct: NWS Phoenix

UPDATE

00Z Aviation Discussion.

KEY MESSAGES

- A quick moving weather system is passing the area to the north today, resulting in brief light showers over portions of Arizona and helping to maintain the seasonably cool temperatures.

- Dry weather and warming temperatures are expected Sunday into Monday.

- Unsettled weather will return Tuesday and again late week, leading to a couple periods with rain chances over South Central Arizona and cooling temperatures near to below daily normals.

SHORT TERM /TODAY THROUGH MONDAY/

The overall progressive pattern continues to evolve, with midlevel water vapor imagery showing a negatively tilted shortwave disturbance passing over the Four Corners and transient ridging nudging eastward/inland along the West Coast ahead of another upper level trough offshore. Despite PHX ACARS soundings (in excellent agreement with GFS bufr soundings) depicting a strong midlevel subsidence inversion on the backside of the shortwave disturbance, a vort max that 500 mb RAP analysis places over northern AZ at this hour, coupled with WAA ahead of a poorly defined near-sfc front, have supplied sufficient lift to release meager instability on the order of 100-300 J/kg and produce scattered low-topped showers over portions of Central and Eastern AZ, especially over the higher terrain and W/SW facing slopes. As the disturbance and any associated forcing slides further east of the forecast area, anticipate shower activity to diminish later this afternoon and through the evening.

Transient ridging will build into the Desert Southwest ahead of the next open wave trough that is expected to pass through the region Tuesday. This has already resulted in increases in H5 heights aloft, currently analyzed at around 572 dam. Ensemble mean H5 heights are advertised to peak around 580 dam as the ridge axis passes directly overhead late Sunday, between the 50th-75th percentiles of climatology for this time of year. Thermal profiles will slowly warm in response Sunday into Monday, with ensemble mean 850 mb temperatures rising from 9C-10C today into a 11C-14C range by Monday. This should yield warming surface temperatures across the lower deserts, with widespread highs in the 70s on Sunday, then near 80F across the typically warmer spots on Monday, 2F-4F above daily normals.

LONG TERM /TUESDAY THROUGH FRIDAY/

Models remain in good agreement that an upper level trough will push inland along the California coast late Monday and progress over the Desert Southwest on Tuesday, albeit in a weakening phase. Rain chances will return to the forecast on Tuesday with NBM PoPs peaking between 60-90% across South-Central AZ, while SW AZ PoPs will range between 20-60%. Latest WPC QPF indicates Tuesday rain totals between 0.25"-0.50" across the Greater Phoenix area, locally higher in thunderstorms, and close to 1.00" over Central AZ higher terrain to the north/northeast. However, there is still considerable spread in the model guidance, with 25th-75th percentile QPF ranging between a few tenths to upwards of 1.25", focused over the higher terrain to the north/northeast of Phoenix. A 1-2 day break in the unsettled weather will then likely ensue following Tuesday, ahead of the next system.

During the latter half of the week, ensembles are pointing towards yet another upper level trough moving inland from the Pacific NW, however, there are still considerable discrepancies in the trajectory of this followup system (how far south it will propagate, which will impact the moisture return and placement of the best upper level ascent mechanisms). Due to this, confidence remains low for PoPs/QPF late in the work week, but at the very least, there is building consensus for an even cooler airmass to enter the region as a result of this second system. Latest NBM highs continue to trend towards the 60s to lower 70s by late week. However, the spread in the model guidance increases considerably on Friday, with IQRs on the NBM forecast temperatures increasing to 8F-10F.

AVIATION

Updated at 2325Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation concerns are anticipated through the forecast period. As a weather system passes through the region, breezy westerly winds will continue for another hour or two before subsiding and switching out of the east. Speeds should remain remain very light (aob 6 kts) overnight. Lower cigs around 6-7 kft will continue to lift and scatter out through this evening.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather issues will exist through the forecast period. Winds will favor a W/SW direction at KIPL, while a N direction will be common at KBLH through tonight. Extended periods of calm and vrb conditions will be likely at both terminals, especially after sunrise tomorrow morning. FEW to SCT low clouds with bases aoa 7 kt will persist over SE California.

FIRE WEATHER

A few weather systems are expected to move through the region over the next week bringing periodic chances for showers and a few thunderstorms to portions of Southern and Central AZ. Dry conditions and temperatures warming near to slightly above normal are expected Sunday into Monday before another weather system moves through the region on Tuesday. Afternoon minimum humidities will range between 30-60% areawide through the next week, following good to excellent overnight recovery. Widespread breezy and locally windy conditions in Southeast CA will develop with the next system on Tuesday. This system will also cool temperatures back into a below normal category. The next weather system will likely reach the area by Friday and result in even cooler temperatures and another round of rain chances.

HYDROLOGY

Gila: A Flood Warning remains in effect from Painted Rock Dam through the Dateland area through at least early next week due to water released from the dam. Water releases remain at 3000 cfs and are expected to remain at this level through the next several days. This will have the potential to flood farm fields and low- water crossings along the river downstream from the dam.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...None.