textproduct: NWS Phoenix

UPDATE...Updated 00z 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/

Overnight and early morning showers and thunderstorms brought widespread rainfall across SC AZ with most of the accumulations in the East Valley, the Foothills and Higher terrains. Going from low to high the western portions of Maricopa County received only an average between 0.05"-0.35", meanwhile in eastern Maricopa County and Pinal County 24hr accumulations were generally between 0.5"-1.25" with localized areas receiving between 2"-2.5" in the higher terrain areas. The later morning hours received a few more lingering storms over higher terrain, where more rainfall occurred but as of this discussion have not been taken into account for the previously mentioned totals. Hi-res CAMs are in good agreement that the systems that developed through the late morning hours will progressively deteriorate throughout the afternoon hours. While PWATs will remain between 1.5"-2" across the region most of the energy has been lost with MUCAPE falling to between 500-750 j/kg this afternoon, with cloud coverage hindering convective potential for further storm development today, although not impossible, especially in the higher terrain due to the natural orographic lift. However, this has lead to PoPs later this morning/early afternoon in SC AZ to be much lower than yesterday's forecast package, dropping from 30-40% to now near 10-25%. As far as temperatures go for this afternoon, highs are expected to be in the low to mid 90s across SC AZ, while the western lower deserts, will be in the low to mid 100s.

By Saturday, broad upper level ridging will be over the Desert SW with the core of the high pressure expected to be over UT and NM. With less storm activity, and broad ridging, skies will begin to clear in the afternoon causing temperatures to climb back into the upper 90s to near 100 in SC AZ and remain in the mid 100s in the western lower deserts. As far as shower/thunderstorm activity Saturday, some isolated to possibly scattered showers and weak thunderstorms are possible over the Arizona high terrain, but the chance of any of this activity surviving into the lower deserts is no more than 10%.

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 2345Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: SHRA activity and potentially some embedded TS Saturday morning will be the main aviation weather issues throughout the TAF period. In the meantime, tranquil weather should prevail through the evening hours and at least into the first part of the overnight hours with winds generally light and variable to light easterly. Heading into the early morning hours on Saturday, the latest hi-res guidance is showing an area of showers and embedded TS developing across portions northern and northeastern Maricopa County, however, to what extent and how close activity will reach the terminal sites is highly uncertain at this time. Therefore, only VCSH have been introduced for the terminal sites for this TAF package. Either way, conditions will improve by the early afternoon hours as the activity tapers off. Similar to today, uncertainty exists whether or not the traditional afternoon westerly shift will materialize on Saturday with winds potentially once again being light and variable to remaining out of the east. SCT-BKN clouds aoa 10 kft will be common throughout the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns are expected throughout the TAF period. Overall wind pattern will remain out of the southeast at KIPL and fluctuate between the south to southeast at KBLH. There is a potential this evening of an outflow from TS activity to the northeast potentially affecting KBLH and temporarily shifting the winds out of the northeast. Overall winds should remain under 15 kts with the potential for periods of light variability early Saturday morning. FEW-SCT clouds aoa 10 kft will be common throughout the TAF period.

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.