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Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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544 FXUS65 KPSR 132121 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 221 PM MST Tue Aug 13 2024 .SYNOPSIS... Temperatures will remain fairly steady over the next several days with highs around 3-5 degrees above average across the lower deserts. Rain chances will decrease substantially through the remainder of this week as dry, westerly flow sets up over the region. The subtropical high will then begin to shift over the Southern Plains this weekend resulting in a slight uptick in moisture this weekend, leading to increasing thunderstorm chances over the AZ high terrain. && .DISCUSSION... Latest mid-lvl water vapor imagery and 500 mb streamline analysis reveals a trough of low pressure centered over the Pac NW while the subtropical high is now displaced east of the region over the Southern Plains. AZ is located between both of these features with westerly flow aloft prevailing. Noticeably drier air is beginning to filter into the western portions of the state, however a subtle shortwave embedded in the large scale trough has helped facilitate ongoing convection across southcentral AZ. We have already seen isolated thunderstorm activity in the Phoenix Metro area, but much of the activity for the remainder of today should be confined to the higher terrain of Maricopa and S Gila counties. As dry air aloft begins to move into the region tonight, storm coverage will diminish with mostly clear skies expected. Lows will fall into the low to mid 80s for most desert communities and into the mid 70s across the foothills. For the remainder of this week, troughing to our north will keep the overall ridge of high pressure suppressed with 500 mb hght anomalies remaining near normal. This will result in highs remaining at or slightly above normal across the lower deserts, or largely below 110 degrees. PWAT values will decrease to the 0.8-1.2" range across the region beginning on Wednesday, which is unfavorable for thunderstorm development. Global ensembles continue to indicate a reinforcing Pacific trough digging across the Intermountain West on Thursday and Friday, which will delay the subtropical ridge from building back into our region. NBM PoPs remain around 5% or less across the entire CWA for Wednesday-Friday. Heading into this weekend, a deeper trough will dig off the coast of the Pac NW, allowing the subtropical ridge to strengthen over NM/TX. This pattern shift will result in a return of southerly to southeasterly steering flow over southcentral AZ and provide a slight uptick in moisture. In response, daily storm chances will return beginning on Saturday. PoPs will mainly be confined to the higher elevations of AZ with only around 10-20% chance of storms surviving into the lower deserts. Temperatures will not fluctuate much through the weekend. Afternoon highs will reach 105-110 degrees across the lower deserts and in the 90-100 degree range in the higher terrain areas. Thus, HeatRisk will continue to be Minor to Moderate with no excessive heat on the horizon. && .AVIATION...Updated at 1830Z. South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Only minimal weather impacts are possible through Wednesday under periods of FEW-SCT mid/high cloud decks. Winds will establish out of the W over the next hour or so, with some gusty, erratic behavior possible with the TS over the Central Valley as it moves off to the northeast. The only terminal expected to have direct TSRA impacts will be KSDL through 20Z. Some isolated shower development (10% chance) will be possible later this afternoon (after 22Z), but confidence is too low to include at this time. Otherwise, west winds may hold well later than usual tonight, and perhaps closer to sunrise Wednesday morning. Southeast California/Southwest Arizona including KIPL and KBLH: No weather issues will exist through Wednesday morning under clear skies. Winds will maintain a southerly component varying between a daytime SE and evening SW component. Gusts may be more prevalent today with 20-25kt possible at both terminals. && .FIRE WEATHER... Scattered showers and thunderstorms will be possible this afternoon and evening across eastern Maricopa and southern Gila Counties. The main threats include localized flooding, frequent lightning, and gusty erratic winds. Drier air will filter into the region through the later half of the week with little to no thunderstorm activity expected. Aside from convectively induced outflow, winds will follow their typical diurnal patterns with gusts up to 15-20 mph each afternoon. MinRH values will range from 15-25% range across the central AZ districts and in the 10-20% range across the CA districts through Friday. Overnight recovery will peak around 25-50% over the next few nights. Temperatures will remain largely unchanged through this weekend with highs running slightly above normal. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Salerno AVIATION...Whittock/18 FIRE WEATHER...Salerno