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Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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040 FXUS65 KPSR 100944 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 244 AM MST Sat Aug 10 2024 .SYNOPSIS... Daily shower and thunderstorm chances will continue through early next week, favoring the higher terrain areas of northern, eastern, and southeastern AZ, with the best chances for activity across the lower deserts for today. By the middle of next week, drier air will filter into the region resulting in a significant downtrend in thunderstorm activity across the entire region. The hottest temperatures during the next week will be today as highs across most of the lower desert communities approach 110 degrees. Starting on Sunday and continuing though the first half of next week, temperatures will cool down slightly with readings closer to normal levels. && .DISCUSSION... Latest water vapor satellite imagery as well as objective analysis depict the subtropical high pressure elongated from west to east from New Mexico through western Texas while to the south of the region, a weak upper-level low is situated across the central Baja Peninsula. Along the northeastern periphery of the Baja low is a weak shortwave that is expected to move into southern AZ later today. This weak shortwave moving into southern AZ in conjunction with the subtropical high to the east will provide divergence aloft across the region and will result in a much more convectively active afternoon and evening today. The latest HREF membership indicates that the highest storm concentration this afternoon and early evening will likely be from western Pima through southwest Maricopa, northern Yuma and La Paz Counties as this is the general region where instability is likely to be maximized with CAPE values nearing 1000 J/KG. Further north and east into the Phoenix area through eastern Maricopa and Gila Counties, although storm activity cannot be ruled out, activity is likely to be more isolated in nature. Another spot that may see isolated storms this afternoon is across the higher terrain of southeast CA, especially over Joshua Tree National Park. With DCAPE values expected to range between 1000-1500 J/KG, strong to locally severe wind gusts along with locally heavy rainfall will be possible with the stronger storms. The overall pattern heading into Sunday and Monday is not expected to change that much with moisture levels remaining elevated as overall PWATs are still expected to average out at 1.5+" and the upper-level low over the Baja Peninsula is likely to send lobes of vorticity into the eastern half of AZ, which along with the favorable thermodynamic environment may help enhance convective activity, especially across southeastern AZ. For Sunday, the latest HREF membership is indicating that southeastern AZ will likely be active with storms developing during the afternoon hours and with the southeasterly flow in place, activity will likely be steered northwestward into south-central AZ. Latest forecast soundings for Phoenix early Sunday evening indicate MLCAPE values ~1000-1200 J/KG with not much convective inhibition in place, thus, it is not out of the question that the complex of storms that develops over southeastern AZ during the late afternoon hours could survive the trip into the Phoenix area heading into Sunday evening. This scenario is being painted by this morning`s 06z HRRR run. More storm activity is possible heading into Monday, with the highest chances at this time across the higher terrain areas east of Phoenix, although activity across the lower deserts of south- central AZ cannot be ruled out depending on how active Sunday turns out. Heading towards the middle to latter of the week, a significant pattern change is expected to occur across the western CONUS as a polar trough is expected to move from the Pacific Northwest through the Intermountain West Region. This will result in southwesterly flow across the region, which will significantly scour out the monsoonal moisture with the latest GEFS and EPS indicating mean PWATs between the Wednesday through Friday time frame decreasing to between 1-1.2" across south-central AZ the lower deserts to less than one inch across the western deserts. Therefore, storm activity is expected to be mostly absent and this is reflected in the latest NBM guidance which shows PoPs across the lower deserts at less than 10% with slight chances remaining across the higher terrain areas of eastern AZ. Heading into next weekend, the ensembles indicate that as the aforementioned polar trough moves into the eastern half of CONUS and the subtropical high rebuilds near Four corners region, a return to easterly flow and thus increasing monsoonal moisture is likely, with storm chances returning. High temperatures today are expected to be the hottest of the next 7 days as highs across most of the lower desert communities approach 110 degrees. Then, starting on Sunday and continuing through early next week, temperatures are expected to slightly cool off with readings returning back closer to normal. Temperatures during the second half of the week may trend slightly warmer but still remain below 110 degrees across the majority of the region. && .AVIATION...Updated at 0525Z. South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Winds will follow typical diurnal tendencies through tomorrow afternoon. That being said, there is expected to be a more prolonged period of SE-S component winds developing during the late morning hours and continuing through most of the afternoon. Once winds turn SW-W in the late afternoon, thunderstorm chances will begin to increase, currently around 15-25% through tomorrow evening. Thus, due to the generally low probabilities right now, no introduction in the TAF`s at this time. However, of higher confidence is outflows that look to be primarily from the southerly direction reaching the metro generally 00z or later, which are currently advertised with a TEMPO group. Sky conditions will generally be SKC-FEW through the overnight hours, become FEW-SCT through the afternoon and then SCT-BKN going into the evening hours with thunderstorm activity across the region. Cloud decks should generally aoa 8-10 kft. Southeast California/Southwest Arizona including KIPL and KBLH: Winds will follow typical diurnal patterns at both terminals with periods of variability. The predominant direction will be southerly at KBLH and southeasterly at KIPL with speeds remaining aob 10 kts. FEW-SCT high clouds will continue through the period. && .FIRE WEATHER... Shower and thunderstorm chances will persist into early next week, mainly favoring the higher terrain areas of AZ, with the best chances and coverage across the lower desert areas this afternoon and early evening. Any thunderstorm will remain capable of producing locally wetting rains and strong winds, with potential for outflow winds to travel long distances and cause sudden wind shifts. Storm activity is expected to trend downward significantly by the middle to latter half of next week as drier air filters into the region. Outside of the thunderstorm activity, the general winds will continue to exhibit the typical diurnal tendencies with the typical afternoon upslope breeziness. MinRHs will remain somewhat elevated through early next week with values of between 20-30%, before trending lower into the 15-25% range heading towards the middle of next week. The hottest temperatures over the next 7 days are expected today as highs across most of the lower desert communities approach 110 degrees. Slightly cooler temperatures are expected starting on Sunday and will persist through the first half of next week as readings trend closer to normal. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Lojero AVIATION...Young FIRE WEATHER...Lojero/Benedict