textproduct: NWS Phoenix

KEY MESSAGES

- Elevated flows will continue on the Salt and Gila Rivers through at least the middle of the week due to recent releases from upstream dams.

- Dry and tranquil weather with slightly above normal temperatures will continue through middle of the week.

- A more unsettled pattern is expected by the weekend with increasing rain chances and cooler temperatures .

SHORT TERM /TODAY THROUGH THURSDAY/

Little has changed over the past 24 hours with upper level ridging remaining in charge across the Southwestern U.S. H5 heights are hovering between 582-585dm, or near the 90th percentile of climatology, which is allowing for a continuation of the slightly above normal temperatures. The weather pattern will start to become more amplified on Wednesday, but it will not initially lead to any changes across our region. Anticipate daytime highs to stay mostly in the lower 80s to at most 85 degrees through Thursday and overnight lows averaging 55-60 degrees. The dry air in place under the ridge will also keep skies clear through Thursday.

LONG TERM /FRIDAY THROUGH MONDAY/

A clear pattern shift later this week is likely to lead to a quasi-blocking flow regime as the flow becoming highly amplified over the eastern Pacific through the entire CONUS and Canada. The ridge over the Intermountain West is expected to extend into southern Canada by Thursday with deep troughing developing off the West Coast and over the Northeastern U.S. Despite the highly amplified flow, the upstream trough to our northwest should be enough to kick the ridge just to the east of our region later Thursday into Friday as a modest shortwave trough peels off from the parent large scale trough. Model guidance is still struggling to come to a full consensus on the track and the strength of the incoming disturbance for Friday into Saturday. Trends over the past couple of days have shifted the system more over Baja and Sonora Mexico while also showing some noticeable weakening as it tracks by just to our south on Friday. A second shortwave trough may also track by just to our north on Saturday.

Despite the lingering model uncertainty later this week, we are nearly assured to have increasing higher level clouds early on Friday followed by some weak lower level moisture advection out of the south during the latter half of Friday. Ensemble mean PWATs are shown to increase to between 175-200% of normal starting Friday, but due to the bulk of the system energy likely bypassing to the south on Friday and to the north on Saturday we are not anticipating widespread rainfall. NBM PoPs are still mostly between 10-25% for the Arizona lower deserts to 20-35% for the higher terrain north and east of the Phoenix area from midday Friday through much of Saturday. Rainfall is expected to be light with total amounts of a trace to at most 0.10" across the lower deserts to localized amounts of 0.10-0.20" over the high terrain. We also can't completely rule out a weak thunderstorm or two on Friday focused across far southern Arizona since forecast MUCAPE does increase to 200-300 J/kg. Temperatures will start to drop on Friday with lower desert highs falling back into the upper 70s to around 80 degrees followed by mid to upper 70s over the weekend. The unsettled weather pattern is expected to continue into next week with even better rain chances by around next Tuesday.

AVIATION

Updated at 1005Z.

No major weather concerns are expected through the TAF period. Light and diurnal winds are expected. Wind speeds are expected to remain light through the period, generally 6 kts or less, with periods of VRB, especially at KSDL, likely. Skies will remain mostly clear aside from a few high clouds passing over southcentral AZ.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns are anticipated through the forecast period. Winds will favor a W-NW component at KIPL and N direction at KBLH, albeit with prolonged periods of nearly calm conditions at both terminals. FEW-SCT passing high clouds will be common through the TAF period.

FIRE WEATHER

Dry conditions and slightly above normal temperatures will prevail through at least Thursday. Minimum humidity values will hover near 25-40% across eastern districts and 20-30% in western districts. This follows fair to good overnight recovery near 30-60% in western areas and good to excellent levels 50-80% in eastern areas. Expect overall light winds, but also some marginally breezy conditions across ridge tops and terrain gaps of eastern districts during the morning hours. A more unsettled weather pattern is expected to settle over the region by the weekend increasing moisture and rain chances and dropping temperatures.

PSR WATCHES/WARNINGS/ADVISORIES

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