textproduct: NWS Phoenix

KEY MESSAGES.

- Dry conditions, partly cloudy skies, and near normal temperatures are expected this weekend.

- Extreme Heat Watches have been issued for the lower deserts of southeast California and southern and central Arizona for much of next week.

SHORT TERM /TODAY THROUGH SUNDAY/

The influence of the upper level trough that brought cooler conditions over the past several days is waining as it continues to weaken and retrograde to the northwest. Moisture levels across the region have fallen to slightly below normal across much of Arizona while slightly elevated moisture levels linger across southern California. These moisture levels are expected to stay fairly stable through the rest of the weekend and likely for much of next week. The subtropical ridge currently centered over the Lower MS River Valley is slated to gradually shift westward over the next several days, eventually becoming fully entrenched across the Southwestern U.S. by around Tuesday. The overall lack of decent monsoon moisture in combination with increasing subsidence from the incoming ridge will mostly inhibit convective potential across our area this weekend and likely well into next week.

As heights increase over the region today into Sunday, warming conditions will push daytime highs back into the normal range. Periods of higher clouds, at times somewhat thick, should help to take the edge off the afternoon temperatures this weekend, but probably not enough to keep lower desert highs from reaching 105 degrees in most spots.

LONG TERM /MONDAY THROUGH FRIDAY/.

The weather pattern for next week will see the subtropical high becoming the dominate feature across the Southwestern U.S. while its strength will barely change. Guidance agrees the ridge center will shift from Texas on Monday to somewhere over Arizona on Tuesday with H5 heights rising to 595-597dm. H5 heights of this magnitude will represent the 97th percentile of climatology for the period and temperatures will follow with forecast highs only falling short of daily records by a few degrees starting Monday. Since moisture levels are now expected to remain fairly limited for much if not all of next week, the day-to-day convective potential should remain quite low and likely confined to far eastern Arizona. The most likely scenario keeps the ridge in full control over the Desert Southwest with the center hovering somewhere over Arizona and/or into western New Mexico.

Forecast confidence for a more prolonged heat event has increased leading us to expand the Extreme Heat Watch through southwest Arizona and much of southeast California, while extending the timeframe through next Friday. NBM forecast highs show readings anywhere from 108-113 degrees across the lower deserts each day next week with overnight lows inching toward the 90 degree mark as early as Tuesday as surface dew points shift a bit higher. Forecast Major HeatRisk has also expanded more across the western lower deserts going into the middle part of next week with the bulk of the area keeping Major HeatRisk levels through at least next Friday. There is uncertainty in the length of time this heat event will last as some of the guidance shows the ridge center may eventually shift more to the north. If this occurs, it should help to increase the amount of monsoon activity over the region, eventually leading to some degree of cooling.

AVIATION

Updated at 0900Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns are expected throughout the TAF period under mid/high cloud decks. The overall wind pattern will exhibit the typical diurnal tendencies with speeds generally aob 10kts.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns are expected throughout the TAF period under mid/high cloud decks. Winds will generally fluctuate between the southeast to southwest, with some modest afternoon and early evening gusts. A period of light variability will be common during the early morning hours.

FIRE WEATHER

Drier conditions and near normal temperatures will prevail this weekend before temperatures rise to above normal next week. Little if any monsoon storm activity is expected over the next several days with only isolated afternoon storms possible over the far eastern districts. Humidity levels will continue to drop with afternoon MinRHs falling into the teens across the lower deserts to around 25% for higher terrain areas starting Sunday. Expect overall light winds generally following typical diurnal patterns.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Watch from Tuesday morning through Friday evening for AZZ530>533-535-536.

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

CA...Extreme Heat Watch from Tuesday morning through Friday evening for CAZ562-565>567-569-570.