textproduct: NWS Phoenix

KEY MESSAGES

- Well above normal temperatures will continue into early next week, with lower desert highs reaching the lower to middle eighties, resulting in areas of Minor Heat Risk.

- A pattern change next week will cool temperatures somewhat and may eventually bring rain chances to eastern portions of the forecast area by late week.

SHORT TERM /TODAY THROUGH MONDAY/

Current midlevel water vapor imagery and objective analysis show a broad area of positive height anomalies associated with West- Central CONUS ridging, and a potent longwave trough over the East/Northeastern CONUS. Undercutting the broad West-Central CONUS ridge, 500 mb RAP analysis places the center of a closed upper low off the west coast of Baja California, continuing its south southeastward trajectory early this weekend. Over the next few days, the overall pattern will progress such that the potent trough over the Northeastern CONUS moves off into the Atlantic, with ridging building in its wake over the Central/Eastern CONUS. Meanwhile, a series of shortwave troughs impact primarily the Pacific Northwest and the closed upper low remains distant to our south, settling off the west coast of the Southern Baja by Sunday before ejecting eastward into Northern Mexico late Monday- Tuesday.

Locally, conditions will remain unseasonably warm through early this upcoming work week, as positive height anomalies (H5 heights in a 575-580 dam range) remain entrenched over the forecast area. Mid and high level moisture transport coupled with divergent flow ahead of the closed low may result in scattered virga/light showers, and perhaps even some isolated t-storms over portions of Southeastern AZ today, but this should remain outside of the CWA. Subsidence and temperatures aloft increase Sunday-Monday as a more potent shortwave impacting the Pacific Northwest pumps up heights downstream and sends a transient ridge axis over the region. NAEFS mean 850 mb temperatures peak around 15C-16C, in excess of the 90th percentile of CFSR climatology, resulting in surface temperatures a few degrees warmer Sunday-Monday compared to today. As such, widespread afternoon highs in the lower 80s can be expected across the lower deserts, with some of the warmest spots even reaching the middle 80s, around 12F-14F above daily normals. Morning lows will also be unusually warm; in fact, the latest NBM gives a 50% probability that the low temperature Sunday will tie or break the record warm value of 57F (set in 1976) at Phoenix Sky Harbor Airport.

Afternoon highs in the 80s translates to Minor HeatRisk, meaning those extremely sensitive to heat may experience heat-related health impacts, especially without adequate hydration. Folks attending outdoor events this weekend should continue to stay hydrated and take breaks in the shade.

LONG TERM /TUESDAY THROUGH FRIDAY/

Ensembles remain in good agreement that another troughing feature will dive down the West Coast starting Tuesday and remain to the west of the region through the middle of the week, bringing an increase in mostly high clouds and gradually lowering heights aloft. Meanwhile, a piece of shortwave energy looks to break from the center of negative height anomalies along the West Coast and move over the Great Basin, bringing meager precipitation chances to the Northern AZ high country Tuesday-Wednesday. Temperatures will cool during the middle of the week in response to this developing unsettled pattern, with lower desert highs generally falling into the middle 70s (still above normal for the time of year.)

Upper level forcing and better quality moisture do not align to bring rain chances to the forecast area until late in the week, when most ensembles agree the lingering trough axis to our west will finally eject eastward. This will bear watching over the next few days, but confidence is still low on this initial system bringing much precipitation due to its short residence time, warming aloft (indicating weakening), and positively tilted axis as it moves onshore. Confidence is increasing, however, on a more potent trough deepening over the Eastern Pacific next weekend and impacting the region early the following week. This might be our best chance at more widespread, appreciable precipitation totals, however details are still unclear this far out.

AVIATION

Updated at 1710Z.

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 Sunday afternoon under periods of mid/high cloud decks. Confidence is good that winds in the Phoenix area should make the shift to westerly later than usual before reverting to easterly mid/late evening. Across SE California, a light N/NW trajectory will be preferred. Prolonged periods of nearly calm conditions will be common across the region.

FIRE WEATHER

Well above normal temperatures and dry conditions will continue into early next week. Afternoon MinRHs will range from 15-25% areawide through Monday, with overnight recoveries generally in a 35-65% range. Winds will remain light, generally below 15 mph through Monday, with a northerly fetch. By the middle of the upcoming work week, a pattern change is expected which will help cool temperatures several degrees (though they will remain above normal), increase humidities slightly, and bring occasionally breezy conditions. Late in the week, a weather system will pass through the region, providing 15-30% chances for wetting rain over higher terrain areas of the eastern districts.

PSR WATCHES/WARNINGS/ADVISORIES

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