textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES.

- A few isolated showers and thunderstorms will remain possible mainly during the afternoon hours today across the Lower Colorado River Valley.

- Near to below normal temperatures are forecast through Saturday before heating back up into early next week as overall dry conditions persist.

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

SHORT TERM /TODAY THROUGH SATURDAY/

Not much has changed in the upper level pattern with broad troughing remaining over the West Coast states and the subtropical ridge over the southern Gulf states. Drying is expected to continue, with the Phoenix area already noticing moderate drying from this morning's sounding with PWATs already dropping to 1.4", compared to yesterday's 1.69" measurement. Though a steady stream of high level moisture continues to be seen on GOES WV imagery across Southeastern CA, and the Lower CO River Valley. This stream of moisture is mostly providing cloud coverage, however with the upper level trough providing extra support for lift, CAMs are continuing to point towards a small chance for showers developing late this evening. However, CAMs were suggesting a similar pattern last night, to no avail, so with the aforementioned cloud coverage in place is seems likely that these models are overestimating convective potential once more.

Starting tomorrow the upper level low over CA will begin to retrograde as the subtropical high begins to rebuilds over the Desert SW region. This will will lead to temperatures climbing back to near normal starting Saturday. In the mean time, today is still forecasted to be below normal with temperatures in the lower deserts ranging between 95F-103F. By Saturday, temperatures are expected to be back near normal or between 100F-105F, and localized areas of Moderate HeatRisk will begin to develop.

LONG TERM /SUNDAY THROUGH THURSDAY/.

The main concern for next week remains the building heat as the subtropical ridge gradually shifts westward back over our region beginning Sunday. H5 heights are expected to climb from 588-591dm on Saturday to 594-596dm Sunday before peaking on Tuesday at around 596- 597dm. Forecast H5 heights Monday through at least Wednesday fall close to the 97th percentile of climatology for the period, but forecast highs remain at least a few degrees below records. An Extreme Heat Watch remains in effect for Monday-Wednesday for the south-central Arizona lower deserts and its very plausible it may need to go through the rest of the workweek as the ridge is not likely to weaken or move much late next week. The latest NBM forecast temperatures for late next week have also been trending up, basically keeping highs around 110 degrees. The main question about the heat will be the amount of convection that may form over eastern Arizona potentially bring outflows into the lower deserts and/or debris clouds. Guidance does agree some modest moisture advection is expected early next week, but it should only be enough to help higher terrain areas. As of right now, there are no clear signs the convective potential will be enough to greatly affect temperatures early next week, so more than likely the current forecast highs of around 110 degrees will hold.

AVIATION

Updated at 2305Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major weather issues will exist through Saturday evening under periods of thick mid/high cloud decks. Confidence is good that TS activity will not impact terminals this evening, and west winds will prevail much later into the overnight than previous days. In fact, the easterly switch may not fully be completed until after sunrise at KPHX.

Southeast California/Southwest Arizona including KIPL and KBLH: Only a 10% chance of TS directly impacting terminals exists this evening, and too low to mention in this TAF package. Otherwise, under a few mid/high cloud decks, winds should oscillate between a SE and SW heading with just some modest afternoon gusts. A light and variable wind may be common for a few hours around sunrise.

FIRE WEATHER

Gradual drying conditions will prevail over the next several days with monsoon storm activity nearly coming to an end and temperatures starting to climb back towards normal. Humidity levels are slated to drop with afternoon MinRHs of 25-35% today dropping into the teens across the lower deserts to around 25% for higher terrain areas starting Sunday. Overnight recoveries will shift from good through Saturday to fair early next week. Winds will remain predominately out of the south southwest much of the period with overnight light easterly downsloping winds over the eastern districts.

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.