textproduct: NWS Phoenix

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/

Broad upper level troughing still resides over the West Coast states, while the subtropical ridge remains centered over the Lower MS Valley. Gradual drying from west to east is still ongoing with guidance showing low level mixing ratios between 8-10 g/kg today dropping to 7-8 g/kg Saturday. The trough is also providing a steady stream of higher level moisture and clouds blanketing southern California while southern and central Arizona sees partly cloudy skies. With the very marginal moisture remaining in place and far from optimal insolation expected later this morning and afternoon, the convective potential is expected to drop further. Hi-res CAMs struggled a bit yesterday, especially with the clouds impacting heating and it seems to be a similar situation for today. CAMs are trying to show some showers and storms forming within the Lower CO River Valley this afternoon, but extensive cloud cover should prevail over that area well into the afternoon. It seems likely the CAMs are overdoing the convective potential as they did yesterday, so PoPs remain under 20% for the western deserts. Only widely isolated showers and maybe a few weak thunderstorms are expected across south-central and eastern Arizona this afternoon.

The additional drying forecast for Saturday should shut down the convective potential for all but the far eastern and northern Arizona high terrain. We also expect the stream of upper level clouds to shift more into Arizona on Saturday leaving mostly cloudy skies for much of our area. Since the trough will hang around today and to a degree through Saturday, temperatures will be slow to warm with highs at or just above 100 degrees today and maybe closer to 105 degrees Saturday depending on the cloud cover.

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 0900Z.

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

No major aviation weather concerns are expected throughout the TAF period under mid to high level cloud decks. The overall wind pattern will exhibit the typical diurnal tendencies with speeds generally aob 10kts. Confidence is good that thunderstorm activity/outflows will remain well removed from the terminals today.

Southeast California/Southwest Arizona including KIPL and KBLH: Isolated thunderstorm activity later this afternoon, resulting in gusty and erratic winds will be the main aviation weather challenge throughout the TAF period. Winds will generally fluctuate between the southeast to southwest with overall speeds aob 10 kts, although some modest afternoon gusts in the mid to upper teens will be possible. Isolated thunderstorm activity is possible during the mid to late afternoon, with a low probability (10-20%) of direct impacts to the terminals with the more likely impact being gusty outflow winds.

FIRE WEATHER

Gradual drying conditions will prevail over the next several days with monsoon storm activity nearly coming to an end. Humidity levels are slated to drop while temperatures warm back to above normal by Sunday. Afternoon MinRHs of 25-35% today will drop 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.