textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- Isolated showers and thunderstorms will remain possible mainly during the afternoon hours today and Friday with the best chances across the Lower Colorado River Valley.

- Near to below normal temperatures are forecast through Friday before heating back up over the weekend into early next week.

- An Extreme Heat Watch has been issued for Maricopa and Pinal counties for next Monday through Wednesday.

SHORT TERM /TODAY THROUGH FRIDAY/

The upper level pattern remains mostly unchanged from this morning with the upper level low over California, and the subtropical far to the east in eastern Texas. With the low over CA southwesterly flow has taken hold over the region with decent moisture being advected into the Lower Colorado River Valley from tropical storms in the Pacific. Current meso analysis shows PWATs near 1.5-1.6" along the Lower Colorado, this moisture in conjunction with extra upper level lift from the low to the west will lead to lingering chances (15- 20%) for isolated storms to develop later this evening. This is supported within hi-res CAMs, highlighting storms developing along the Lower Colorado River Valley into Southern Mohave County. For the rest of the lower deserts chances for showers tonight are far more limited, with a 10-15% chance of isolated showers possible, mostly focused in the eastern portions of south central AZ and the higher terrain areas. By Friday Shower and thunderstorm activity will decrease further, as drier air will begin to scour out the current moisture in the atmosphere.

Even though shower and thunderstorm activity will be decreasing through today and Friday, the good news will be that afternoon high temperatures will remain 4F-6F below normal through the rest of the work week, thanks to the low remaining stationary over CA. This translates to highs across the lower deserts between 96-103, and widespread Minor HeatRisk. Morning lows will also be quite pleasant Friday morning, ranging in the upper 70s to lower 80s.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

The weather pattern will shift over the weekend into early next week as the subtropical ridge once again becomes the dominant weather feature across the Southwestern U.S. The Pacific trough will somewhat stick around into Saturday, but it is shown to quickly lift to the north by Sunday as the ridge moves back in from the east. Forecast H5 heights rise from 588-590dm on Friday to 591-594dm Saturday before peaking around 594-596dm during the first half of next week.

The dry air and increasing subsidence this weekend should keep all but a few eastern Arizona high terrain showers and storms from developing. Temperatures will warm up quickly over the weekend with the expansion of the ridge with NBM forecast highs reaching 103-106 degrees Saturday and 106-109 degrees Sunday. The drop in moisture will at least push surface dew points well into the 50s this weekend to as low as the upper 40s early next week. This will help to keep overnight lows close to normals through the weekend before we heat up further next week. Ensembles eventually show the ridge center shifting directly over Arizona by around Monday, likely staying in place for a few days. The increased subsidence from the ridge with no meaningful moisture return happening early next week should keep lower desert PoPs below 10% to at most 10-20% over the far eastern Arizona high terrain.

As the modestly strong (90-97th percentile of climatology) ridge settles over Arizona during the first half of next week, temperatures are likely to heat up enough to result in Major HeatRisk across portions of the lower deserts. The highest likelihood for Major HeatRisk looks to impact the Phoenix metro with daytime highs around 110 degrees and lows around 90 degrees starting Monday, but the more rural lower desert areas should experience similar daytime highs as well. Due to the expectation of Major HeatRisk, we have issued an Extreme Heat Watch for Maricopa County, to include the Phoenix Metro, and Pinal County, valid from Monday through Wednesday

AVIATION

Updated at 0505Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major weather issues should exist through Friday evening under periods of thicker mid/high cloud decks. Some variability may exist in wind directions late evening before settling on an easterly direction overnight. Similar variability may occur early Friday afternoon before transitioning back to a westerly direction. Confidence is good that TSRA/SHRA will remain well removed from PHX terminals Friday.

Southeast California/Southwest Arizona including KIPL and KBLH: Isolated TSRA Friday afternoon may impact SE California terminals with direct impacts, however probabilities (~10%) are too remote to include in this TAF package. The most likely effect will be gusty outflow winds and potential abrupt wind shifts. Otherwise, winds should oscillate between SW and SE with only occasionally stronger gusts as thicker mid/high cloud decks remain common.

FIRE WEATHER

Elevated humidity levels, below normal temperatures, and lingering chances for showers and a few thunderstorms are expected today before much drier air filters into the region Friday into the weekend. Afternoon MinRHs of 30-50% today will drop to 20-30% by Saturday and into the teens across the lower deserts starting Sunday. Overnight recoveries will remain good to excellent. Winds will remain predominately out of the south southwest much of the period with overnight light easterly downsloping winds over the eastern districts. Temperatures will warm back to normal by Saturday and then above normal starting Sunday.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Watch from Monday morning through Wednesday evening for AZZ534-537>544-546-548>551-553>555-559.

CA...None.