textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES.

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

- Extreme Heat Warning will be in effect for the lower deserts of southeast California and southern and central Arizona for much of next week.

SHORT TERM /TODAY THROUGH TUESDAY/

Southwest flow during the monsoon is not ideal for rain chances, especially across the lower deserts, unless there was a tropical system, which there is not, or a trough moving through, which there also is not. So, pretty quiet monsoon conditions are expected this weekend through the beginning of next week as the southwest flow aloft persists, with near to slightly below normal moisture levels. Dew point temperatures will actually be on the decline through Monday, with guidance showing most lower deserts falling to 50-55 degrees in the afternoons and possibly even dipping below 50 degrees in some locations. A few weak showers or storms may still develop over terrain favored areas today, but instability is very low (couple hundred J/kg CAPE at most). So, updrafts will struggle and be short lived. With lowering dew points instability will be even less the next few days. Latest HREF neighborhood probability and paintballs for >40dBZ radar echoes shows almost no coverage for Sunday afternoon, except for far southeast AZ. There will be weak to moderate ascent for some light showers late tonight through Sunday morning across SoCal and western AZ, from a passing shortwave trough, but likely not enough rain will reach the ground to measure (>0.01").

Strong high pressure is still seen on satellite displaced well to the east, over the southern Mississippi River states, and large scale troffing is positioned to the west. Height fields over the local area have steadily risen over the past couple of days and latest objective analysis shows H5 heights around 592-594dam, which is close to the 90th percentile of climatology. Temperatures at 850mb have also warmed a few degrees. This will lead to surface temperatures this afternoon peaking near normal, in the 102-106 degree range for the lower deserts. Around 2-3 degrees of warming is expected into Sunday and another 2-3 into Monday, which will bring a return of highs reaching or exceeding 110 degrees in the lower deserts and Major HeatRisk beginning Monday. The Extreme Heat Watch has been upgraded to a Warning starting Monday for all areas previously under the Watch. The coverage of Major HeatRisk becomes more widespread by Tuesday as temperatures continue to warm, with highs forecast to reach 5-7 degrees above normal and low temperatures warming back into the upper 80s to around 90 degrees in the lower deserts.

LONG TERM /WEDNESDAY THROUGH SATURDAY/.

The weather pattern for most of 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 by Wednesday 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 each day. Since moisture levels are now expected to remain fairly limited for much of, 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.

There is moderate to high confidence for a more prolonged heat event leading to the now Extreme Heat Warning covering all lower deserts and extending through Friday. NBM forecast highs show readings anywhere from 108-113 degrees across the lower deserts each day next week with overnight lows near the 90 degree mark by Tuesday- Wednesday 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 and/or east. 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 2300Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No weather concerns will exist through Sunday evening under periods of mid/high cloud decks. Wind behavior will be nearly identical to the past 24 hours featuring a later than usual overnight easterly wind shift, and extended periods of variable directions.

Southeast California/Southwest Arizona including KIPL and KBLH: No weather issues will exist through Sunday evening under occasionally thick mid/high cloud decks. Trends in winds will be similar to the past 24 hour including modest afternoon/evening gusts, and periods of nearly calm conditions in the morning.

FIRE WEATHER

Dry 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 through Monday 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 Warning from 10 AM Monday to 8 PM MST Friday for AZZ530>544-546-548>551-553>555-559.

CA...Extreme Heat Warning from 10 AM Monday to 8 PM PDT Friday for CAZ562-565>567-569-570.