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Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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023 FXUS65 KPSR 170528 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1028 PM MST Tue Jul 16 2024 .UPDATE...Updated 06z Aviation Discussion. && .SYNOPSIS... Daily rain chances continue over the next several days, with most activity remaining over the higher terrain areas. Moisture, along with rain chances, start to increase over the lower deserts as we approach the end of the workweek and through the weekend. Temperatures will remain above normal with Friday and Saturday expected to be the hottest days of the week. Widespread HeatRisk will continue with increasing areas of Major HeatRisk across the lower deserts on Friday and Saturday. && .DISCUSSION... Upon analysis of upper-level WV satellite imagery this afternoon, the high pressure system is still centered over northern New Mexico. This high pressure will slowly move westward through the week. As the high pressure system moves over head, there will be increased subsidence aloft leading to slight drying. However, there will still be enough moisture to promote daily thunderstorm activity over the Arizona higher terrain. The set up for today and tomorrow will be fairly similar to yesterday. There will be marginal instability, and the environment over the lower deserts is expected to remain capped. Therefore as storms move off the higher terrain and into the lower deserts they will weaken and fall apart. There is still a decent amount of DCAPE in place, values in the 1500-2000 J/kg range. This will support long traveling outflow boundaries, that could impact lower elevations with some gusty winds. The HREF, shows a 10-30% chance of wind gusts over 35 mph getting into central Maricopa and Pinal counties this evening. As the high pressure migrates over Arizona and into eastern Nevada late this week and into the weekend, global ensemble members show an increase in PWATs to around 1.5". This will lead to increasing thunderstorm chances across the lower deserts across south-central Arizona, with PoPs around 20% Thursday-Saturday. In addition to the rain and storm chances, temperatures will also be on the rise through the week as the aforementioned high pressure system migrates westward. The hottest days of the week are expected to be on Friday and Saturday, with forecasted afternoon high temperatures in the 110- 120 degree range and the hottest day currently forecasted to be on Saturday. HeatRisk will also be on the rise, with major HeatRisk becoming isolated across the lower deserts on Friday and more widespread on Saturday. With the increasing HeatRisk, excessive heat products may be needed. As we head towards the end of the weekend and into next week, the high pressure system will continue to migrate westward and looks to eventually settle over Nevada. In addition there will also be a trough pushing into the Planes. This will promote diffluence aloft, and lead to an even more favorable synoptic pattern for increased monsoon activity. This is reflected in the NBM guidance with PoPs increasing to 40-50% across the south-central AZ lower deserts on Sunday and Monday. The overall steering flow will be out of the north/northeast, which will send storms that develop over the Rim into the lower deserts. We will need to continue to monitor the trend in the overall flow pattern, as historically, northeasterly flow events have led to severe weather materializing across the Phoenix area. So this will bear watching as we get closer to the weekend once the overall mesoscale details start to become clearer. In addition to these increasing rain chances, temperatures will also cool slightly heading into next week as that high pressure system settles over Nevada. && .AVIATION...Updated at 0530Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Outflows emanating from recent shower/storm activity remains the biggest uncertainty at this point, at least for KPHX and KIWA, due to the rapid decay of the gust front as it moves southward. At this point, expecting both terminals to remain out of the southwest, with a chance of variable winds if the gust front reaches either terminal. Otherwise, light and variable winds expected to settle into the metro through the overnight hours, with KIWA the highest chances of having a discernible southeasterly wind develop going into tomorrow morning. Winds will then go westerly with afternoon gusts 15-20 kts. Outflows will again be a possibility tomorrow evening with convective activity in the higher terrain. Best chances will be out of the easterly or northeasterly direction, but probabilities are too low to include in this TAF package. SCT-BKN into the overnight hours will clear to FEW-SCT by tomorrow morning and remain this way until the evening hours where skies will become more cloudy due to convection nearing the metro. Southeast California/Southwest Arizona including KIPL and KBLH: Typical diurnal winds are expected to continue, with SE at KIPL and S-SW at KBLH. Limited convective activity across the region will only provide a very low (<10%) chance of an outflow reaching either terminal through the forecast period. Skies will remain FEW-SCT through the period. && .FIRE WEATHER... Sufficient moisture will remain in place to result in daily thunderstorm activity through the next several days, with activity mainly confined to the AZ high terrain through midweek. Thunderstorm chances start expanding into the lower elevations by the latter half of the week and through the upcoming weekend. Gusty, erratic winds will be the biggest hazard with these thunderstorms, exacerbating issues on any ongoing wildfires and new starts. Aside from the thunderstorm winds, the typical afternoon upslope gustiness upwards of 20-25 mph will be common. MinRHs during the next several days will range between 10-30% with fair to good overnight recoveries between 30-60%. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Berislavich AVIATION...Young FIRE WEATHER...Berislavich/Lojero