textproduct: NWS Phoenix

UPDATE...12Z Aviation Discussion

KEY MESSAGES

- Shower activity will gradually diminish this morning with only isolated chances mainly during the afternoon. Typical monsoon shower and thunderstorm chances will then favor the Arizona high terrain this weekend.

- Below normal temperatures are expected across much of Arizona today through early next week while southeast California maintains near normal readings.

- Thunderstorm chances should increase during the first half of next week with lower desert chances by Tuesday.

SHORT TERM /Today through Saturday/

A weakening MCS is currently sitting over the Phoenix foothills and higher terrain north of Phoenix. Rainfall rates have diminished considerably since last evening with most locations staying under 0.25" hour. A pocket of moderate rain showers with some embedded thunder remains farther to the north between Phoenix and Flagstaff. Despite the modest ascent still in place, the atmosphere has become less and less unstable. Hi-res CAMs are in fairly good agreement this MCS will continue to dissipate through sunrise with the best chance of any additional development from western portions of Phoenix through the rest of western Maricopa County. We are expecting to allow the Flood Watch to expire at 12Z even though some additional showers are likely during the morning hours. Given the low instability environment and the extensive cloudiness that is likely to last into the afternoon hours, additional destabilization is not likely to be enough to spark off much if any convection this afternoon. Drier air will also start to work into southwestern and then central Arizona later today. Temperatures will struggle to warm into the 90s across the south- central Arizona lower deserts this afternoon, while highs across southeast California and portions of western Arizona should top 100 degrees under at least partly sunny skies.

Guidance is finally in good agreement the drying should extend far enough through central Arizona that Saturday will be an overall quiet weather day for much of the area. Some isolated to possibly scattered showers and weak thunderstorms are expected over the Arizona high terrain, but the chance of any of this activity surviving into the lower deserts is no more than 10%. Temperatures will begin to recover on Saturday with mid to upper 90s in the Phoenix area, but higher than typical humidities will still make it feel uncomfortable.

LONG TERM /Sunday through Thursday/

The easterly wave currently centered over west Texas will undergo some weakening into the weekend, but guidance shows it finally drifting west southwestward closer to our region by Sunday. Sunday still looks to be an overall quiet day as moisture should still be limited, but with increasing higher level ascent any convection that builds over the Arizona high terrain should be more robust. Some guidance is even hinting at pushing some rain into the lower deserts at some point Sunday evening or Sunday night, but that is of low confidence at the moment.

By Monday into Tuesday, the easterly wave is likely to be moving into southeastern Arizona with moist easterly flow spreading over the region again on Monday. Whether enough moisture will advect into the area for lower desert convection to occur on Monday is still unknown, but it seems likely at least one day during the first half of next week will be a fairly active monsoon day. We may even have to worry about severe wind threat by around Tuesday as mid level winds are shown to increase enough to pose a threat for longer lasting storms and/or MCS developing and making it off the high terrain. Of course, this is still quite uncertain as it will depend on the strength and the progression of the easterly wave. Guidance shows the disturbance eventually moving to our west by next Thursday as the subtropical high is favored to become more established over New Mexico or Texas. Depending on how far south and west the high sets up, we may be in for another drier and hot monsoon period by next weekend. Chances look decent for at least a downtrend in rain chances late next week or by next weekend as guidance favors the gradual downtrend in moisture over the region.

Temperatures are forecast to gradually creep upward next week, but locations across south-central and eastern Arizona are expected to stay below normal for at least the first half of the week. The western lower deserts are likely to stay in the normal range much of the week. If the ridge does eventually set up just to our east, we may eventually have to deal with highs topping 110 degrees again by next weekend.

AVIATION

Updated at 1050Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Area radars indicate shower activity is tapering down across the region, however there could still be isolated SHRA/VCSH over the metro terminals through sunrise this morning. There is a low chance (<20%) of additional SHRA/TSRA developing this afternoon but confidence remains low in overall timing and coverage. Winds will generally be out of the east throughout most of the afternoon with a later than usual SW shift anticipated at KPHX by early this evening. SCT-BKN mid to high clouds aoa 10 kft will be common throughout the TAF period along with a SCT cu field around 6-8 kft.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are expected during the next 24 hours under passing mid to high cloud decks. Winds will generally remain out of the southeast at KIPL before shifting out of the southwest late tonight. Winds will remain predominately southerly at KBLH. Speeds at both terminals will remain aob 10 kts through this evening.

FIRE WEATHER

Showers and thunderstorms will remain possible over the Arizona districts into this afternoon with much lower chances into western districts. Activity over south-central Arizona will still be capable of producing localized flooding through early afternoon before drying begins to move in from the south. Elevated southerly winds are anticipated much of the period for the western districts with light winds elsewhere. Elevated humidities today will keep minimum afternoon humidity levels from 30% in western districts to 40-50% over the eastern districts. A gradual drying trend over the weekend will drop MinRHs to 20-35% with any wetting rain chances favoring the Arizona high terrain.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None.

CA...None.