textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- Dry and tranquil weather conditions are expected through this weekend with near zero rain chances.

- Near to slightly above normal temperatures are expected through at least this weekend with afternoon temperatures near 100 degrees across the lower deserts.

- A low pressure system and moisture return early next week will bring a return of rain chances to at least the high terrain of northern and eastern Arizona.

SHORT TERM /TODAY THROUGH SUNDAY/

Drying conditions with near to slightly above normal temperatures are expected today through this weekend. It is still muggy at the surface in south-central AZ, including Phoenix, with dew point temperatures in the 60s to near 70 degrees early this morning, but dry air has moved in aloft, which is partly why there were no addition showers and storms Thursday after the very wet Wednesday. PWATs at midnight yesterday were around 1.7-1.9", but have since dropped to 1.0-1.2" and will continue falling today through Saturday. Surface moisture will also steadily scour out today through Saturday, falling into the 50s by this evening and into the 40s by Saturday evening in south-central AZ. It will be even drier west of Phoenix. The abundant dry air that will be moving through can be seen upstream on water vapor satellite imagery.

Satellite also shows a shortwave moving through southeast AZ, which may provide just enough forcing to spark isolated showers and storms in the White Mtns this morning and early this afternoon, possibly clipping portions of southeastern Gila County. There is also a broad upper level low situated over the Northwest CONUS. This low will gradually track eastward through this weekend and help suppress H5 heights over the Desert Southwest and thus moderating the temperatures. Temperatures will be nearly the same each day, with morning lows in the 70s and afternoon highs around 97-103 degrees across the lower deserts. Normal highs are right around 100 degrees for mid-September. These temperatures will be a nice reprieve, especially the mornings, but will still result in Minor HeatRisk.

LONG TERM /MONDAY THROUGH THURSDAY/

Heading into early next week, there is good confidence that a Pacific low will move to the central/southern coast of California by the end of the day Monday. Exactly how this low evolves once reaching the coast is still a little uncertain, but latest model consensus suggests the low will track ENE inland staying mostly north of the local area and driving a chance for showers and storms across northern AZ. Conceptually this is not a bad setup for a transitional severe weather event with potential frontogenetical forcing and a moderately strong upper level jet with higher shear, but rebounding quickly from the very dry air this weekend and getting sufficient moisture in here to support any lower desert rain chance will be tough. Model guidance does at least support a slow return of moisture Monday through next week, more so coming from the southeast like typical early stages of the monsoon.

Model guidance is also pointing toward a strong ridge developing through the middle of the U.S. with the subtropical high restrengthening near/over Texas by mid to late week. This would keep the Desert Southwest under predominant southwest flow which is not the most ideal setup for lower desert storm chances, especially not for southeast CA and southwest AZ. Latest NBM forecast has PoPs focused primarily across northern and eastern AZ each day next week with only minor (10-20%) PoPs for south-central AZ lower deserts in the evenings. The one thing this pattern does open the door for, the longer it persists, is potential Eastern Pacific tropical moisture advecting north.

Temperatures through next week will mostly stay the same day-to-day, with highs in the upper 90s to lower 100s, which will be around 2-5 degrees above normal, and lows remaining mostly in the 70s. The temperatures will lead to widespread Minor HeatRisk through at least the first half of the week with a trend toward areas of Moderate HeatRisk by the second half of the week as morning low temperatures creep back up.

AVIATION

Updated at 1715Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major weather issues will exist through Saturday afternoon under a few mountain cumulus build-ups and patchy high cirrus. Confidence is good that east winds will only gradually switch to westerly mid/late afternoon with a prolonged period centered around a southerly cross runway trajectory (i.e. 140v230) with speeds nearing 10kt. A reversal back to easterly is not likely until after midnight.

Southeast California/Southwest Arizona including KIPL and KBLH: No weather issues will exist through Saturday afternoon under clear skies. Winds will favor a W/NW direction at KIPL and S/SW trajectory at KBLH. Speeds should remain under 12kt with limited gusts, and extended periods nearly calm conditions or light northerly in the morning.

FIRE WEATHER

Overall there are no fire weather concerns through the next week. A drying trend will continue today through this weekend. With no rain expected through at least the start of next week. Minimum RH values this afternoon will be around 20-35% across south-central AZ to 10- 20% across southeast CA and southwest AZ. The minimum RHs will then dip to 10-20% for nearly all areas this weekend. Overnight recoveries across south-central AZ will still be good tonight at 45- 75%, but then falls lower this weekend. There will be a gradual return of moisture next week, best across eastern AZ and there will be an increase in rain chances again, but as of now rain chances look to primarily favor northern and eastern AZ high terrain. Besides a potential increase in breeziness early next week with a weather system, winds will mostly follow typical diurnal patterns with modest afternoon upslope/upvalley gustiness (15-25 mph).

PSR WATCHES/WARNINGS/ADVISORIES

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