Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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391 FXUS65 KPSR 162118 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 218 PM MST Tue Jul 16 2024 .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 1205Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: W to SW winds will prevail through this afternoon and evening at all terminals with afternoon speeds up to 10-15 kts and gusts to around 20 kts. Confidence in outflows passing through the terminals is not as high as previous days. There is at least a low chance for one from the E or NE this evening, after 3-4Z. An outflow from the S may also coincide with an increase in low-level SW winds closer to and just after midnight (7Z). Chances of VCSH/VCTS are low this evening-tonight, 10% or less. Confidence in a full E to SE wind shift Wednesday morning at all terminals is low to moderate. If it does shift at KPHX, it may be for only a few hours before shifting back W to SW by 16-17Z. FEW cumulus this afternoon will be around 10-12K ft AGL, then SCT to occasional BKN mid-level clouds around 14K ft will pass over the area this evening- tonight. Southeast California/Southwest Arizona including KIPL and KBLH: Winds will prevail out of the E-SE at KIPL, with potential for a brief turn to the S-SW late this evening, and S-SW at KBLH through the TAF. Speeds will remain around 10 kts or lower at KIPL while KBLH see speeds around 10-15 kts, and gusts to around 20 kts at times, through most of the TAF period. FEW to occasionally SCT mid and high level clouds will pass over the area. There is a slight chance (10-20%) of some spotty high-based convection passing through the area Wednesday morning-midday. && .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...Benedict FIRE WEATHER...Berislavich/Lojero