textproduct: NWS Phoenix

KEY MESSAGES

- Near normal temperatures with a decent amount of clouds are expected this weekend. - Hotter temperatures will return early next week creating Moderate to Major Heat Risk by Tuesday and lasting through at least Thursday.

- An Extreme Heat Watch has been issued for Tuesday through Thursday across the lower deserts, including Phoenix, Yuma, and El Centro. Forecast highs are currently 111 to 116 degrees.

- Dry conditions will prevail, although a sprinkle cannot be ruled out Saturday into Sunday, before isolated storm chances return over the Arizona high terrain later next week.

SHORT TERM /TODAY THROUGH SUNDAY/

Upper level ridging has mostly taken over across the Desert Southwest, but a decaying tropical system west of Baja will continue to bring considerable high level cloudiness to the region today into early Sunday. H5 heights have risen over the past couple of days leading to rising temperatures, but readings today may end up falling short of Friday's highs due to the clouds. Guidance also shows a wing of vorticity swinging northward through the area this afternoon while moisture aloft descends more into a 14-20K feet layer. The resultant weak forcing from the vorticity axis is expected to be enough to bring some very high based virga showers focused during the afternoon and early evening hours today. Some locations are expected to feel some sprinkles at times, but the chances of any actual measurable rainfall remains near zero.

After the trough axis shifts northward out of the area by early Sunday, some drying aloft will help to gradually disperse the high clouds from west to east. The increased insolation on Sunday should result in daytime highs reaching near 110 degrees for some locations. The subtropical high into Sunday will also remain centered well to our east southeast creating a more favorable fetch of southerly flow and leading to some improving boundary layer moisture. Even though moisture will improve over the next few days, it will still fall well short of what would be needed for any monsoon convection to develop.

LONG TERM /MONDAY THROUGH FRIDAY/

Forecast confidence has increased in a more pronounced period of very hot conditions for next week. The subtropical ridge is expected to gradually shift right over the region Monday into Tuesday with guidance now favoring some strengthening of the high going into mid week. Forecast H5 heights are shown rising to between 594-596dm by Tuesday before peaking between 595-597dm, or well within the 90th percentile of climatology.

NBM guidance over the past 24 hours has trended noticeably warmer for the middle part of next week, mostly due to the higher heights but also somewhat due to less than previously expected moisture moving into the area. NBM forecast highs have increased by around 2F for Tuesday-Thursday putting much of the lower deserts into a 112-116 degree range. This heat episode is very likely to bring our hottest temperatures so far this summer. The uptick in forecast temperatures has led us to issue an Extreme Heat Watch for Tuesday-Thursday for all of the lower deserts across southeast California and southern and central Arizona. Model guidance is still trying to have the ridge shift more to the west later next week, potentially recentering to off the southern California coast. If this occurs, it should lower temperatures a couple of degrees by next Friday, but just as important is the potential for additional moisture advecting northwestward into the area. There is still a good amount of uncertainty with this potential moisture increase as it will largely depend on the position of the high center. If the high center does end up moving far enough to the west, this scenario should allow for at least enough of a moisture increase and weakening subsidence to bring some high terrain showers and storms. Any chances for the lower deserts is more likely than not to hold off until next weekend.

AVIATION

Updated at 0900Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

No significant weather concerns will exist through the TAF period under periods of thicker mid/high cigs. With these cigs, expansive areas of virga and potentially an isolated SHRA/some areas of sprinkles will be likely at any point from the late morning through the evening, but with limited impact to operations. Trends in wind shifts and speeds should be similar to the past 24 hour with wind speeds mainly aob 10 kt.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major weather concerns will exist through the TAF period under periods of thicker mid/high cigs, occasional virga, and potentially an isolated SHRA/a few areas of sprinkles. Chances for operational impacts from cigs/SHRA remain too low to include in this TAF package. Confidence is good that winds will generally shift between SSE and SW with modest afternoon/early evening gustiness. Periods of light and variable to near calm conditions are expected this morning at KBLH and from mid morning through the afternoon at KIPL.

FIRE WEATHER

High pressure will remain in control well into next week with near normal temperatures this weekend warming to above normal by Monday. Afternoon humidities will fall to around 10% each day through Monday with overnight recoveries gradually improving to 25-40% early next week. Winds will continue to follow diurnal upslope/downvalley patterns with modest upslope afternoon breeziness. Despite the diminished winds, seasonably elevated fire danger will likely persist into next week due to dry conditions and dry fuels. Moisture is expected to gradually increase over the region next week next week, but overall dry conditions should persist with any chances for wetting rains holding off until late next week at the earliest.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Watch from Tuesday morning through Thursday evening for AZZ530>534-536>551-553>555-559-560-562.

CA...Extreme Heat Watch from Tuesday morning through Thursday evening for CAZ562-564>570.