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Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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169 FXUS65 KPSR 121110 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 410 AM MST Mon Aug 12 2024 .UPDATE... Updated Aviation && .SYNOPSIS... Showers and storms will be again be possible this afternoon and evening, but activity will mainly favor the higher terrain locations. Drier air will work it`s way into the region for the middle of the week causing a significant downtrend in monsoon activity. Moisture looks to rebound slightly by the end of the workweek and heading into the weekend leading to storm chances returning to the region, mainly for the higher terrain locations. Temperatures will remain largely unchanged through the week and run slightly above normal. && .DISCUSSION... The overall synoptic pattern remains largely unchanged from the past few days. The subtropical high pressure system is still centered over Texas and stretches back westward into eastern Arizona. The weak upper-level cyclonic circulation also remains situated over the northern Baja peninsula. There is also a polar trough starting to digging off the coast of the Pacific northwest. The leftover MCV from yesterday morning`s activity can still be seen spinning in southwestern Arizona and is slowly making its way into southeastern California. Another weak mid-level wave can be seen in northwestern Mexico and it is expected to move into southeastern Arizona later this afternoon sparking convection down there. PWATs are in the 1.5- 1.7" range with this wave and the leftover MCV in southwestern AZ, elsewhere PWATs range from 1.0-1.4" across the region. This is ample moisture to support the development of storms later today, especially in the higher terrain of Arizona. The environment does support some showers and storms across south-central AZ, including the Phoenix Metro, this evening. Latest forecast soundings show MUCAPE values in the 1000-1500 J/kg range and do not show much in the way of convective inhibition for this afternoon and evening. One thing that may limit storms across the lower deserts this evening is the lack of moisture. Models have been over doing PWAT values by ~0.2" and are initializing with PWAT values too high. Hi-res guidance does continue to show storm activity struggling to survive into the lower deserts this evening. With southerly/southeasterly flow in place, convection surviving into the lower deserts tonight will likely depend on how robust the storms in southeastern Arizona get later today and if we can get deep/colliding outflow boundaries. Tuesday will be the transition day for the overall synoptic pattern. The aforementioned polar trough will continue to dig into the Pacific northwest. This will lead to drier air starting to make its way into the region, especially across the lower elevations. With this drier air starting to make its way into the region any storm activity on Tuesday afternoon and evening is expected to remain across the higher terrain of eastern Arizona. A big pattern change is still expected for the middle to latter half of the workweek. The polar trough will continue to move into the Pacific northwest causing the subtropical high pressure system to relax and stretch out even more. With this pattern change we will see the flow aloft become southwesterly, which will user in drier air with PWATs decreasing to around 0.8-1.2" across the CWA. This is unfavorable for monsoonal activity and will likely result in little to no shower or storm activity across the CWA for the middle part of the week. Heading into Friday and the weekend, the subtropical ridge will start to build once again across the southern Plains. This will result in a return to southerly/southeasterly flow aloft. This shift in the flow pattern aloft will allow for a slight increase in moisture, with global ensembles showing PWATs returning to the 1.2- 1.4" range across the CWA. This increase in moisture will result in an increase in shower and storm activity, with most of the activity expected to be confined to the higher terrain locations. Temperatures this coming week are forecasted to remain largely unchanged. For the lower desert communities, afternoon high temperatures are forecasted to be in the 100-110 degree range through the week. For the higher terrain areas, afternoon high temperatures are forecasted to be in the 90-100 degree range. Thursday and Friday are currently forecasted to be the hottest days of the week. With temperatures being near to slightly above normal, HeatRisk will be in the Minor to Moderate range across the region. && .AVIATION...Updated at 1110Z. South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Chances for at least one outflow boundary and abrupt wind shift with isolated storms on the fringes of the airspace this evening will be the greatest weather concerns. Winds this morning may not fully complete the easterly switch, and variable directions may be more common before returning to a westerly fetch prior to noon. Cloud decks 080-120ft AGL should also start to develop over higher terrain areas with daytime heating. Models suggest the most likely outcome being southerly outflows sweeping into the metro early evening though other directions cannot be completely precluded. If storm origins are more to the SW, then outflows may become absorbed into the general west flow and not create any immediate operational impact. Chances of direct TS impacts are under 20%, so not included in this TAF package. Eventually by mid/late evening, forecast confidence is moderate that E/SE winds will eventually envelop the metro and predominate at all terminals through the overnight. Southeast California/Southwest Arizona including KIPL and KBLH: Only the outside possibility of isolated TSRA around the region would pose a weather impact under mostly clear skies. Any storm coverage late this afternoon appears too isolated to include in this TAF package. Otherwise, some form of a southerly wind component will be preferred with occasional gustiness to 20 kt. && .FIRE WEATHER... Shower and thunderstorms chances will continue today, with the best chances confined to the higher terrain locations. Shower and thunderstorm chances tomorrow will be limited to just the higher terrain locations. With any thunderstorm activity, there will be strong winds along with the potential for gusty outflows to travel long distances and cause sudden wind shifts. Thunderstorms will also contain localized heavy downpours and frequent lightning. Drier air will move into the region for Wednesday and Thursday with little to no thunderstorm activity expected. Aside from thunderstorm winds, the overall general winds will tend to follow their typical diurnal tendencies with some afternoon upslope breeziness. MinRH values today will be in the 20-30% range with a downward trend for the middle of the week with MinRH values in the 10-25% range. Overnight recoveries will be in the 30-50% range. Temperatures though the week will remain largely unchanged and run near to slightly above normal. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Berislavich AVIATION...18 FIRE WEATHER...Berislavich