Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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345 FXUS65 KPSR 031018 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 318 AM MST Mon Jun 3 2024 .SYNOPSIS... Temperatures a few degrees above normal over the next couple of days will soar towards record levels mid to late week, resulting in Excessive Heat Watches in effect for most of the region Wednesday-Friday. Temperatures will then trend cooler going into and through the weekend as the strong high pressure in place late week will weaken. && .DISCUSSION... Upper level troughing pushing into the Pacific Northwest early this morning is sending down some scattered sky conditions across the western districts. There will be no impacts from this system aside from periodic scattered to broken skies over the next couple of days. The main weather concern for this week centers around a building ridge across western CONUS that will cause temperatures to soar to near/at/above record levels mid to late week. Excessive Heat Watches remain in effect Wednesday and Thursday, but have also been extended through Friday as more widespread Major HeatRisk is anticipated based on latest trends in ensemble guidance. Somewhat zonal flow will continue through Tuesday, as the latest shortwave trough across the Pacific Northwest ejects eastward over the next couple of days. Dry conditions, with temperatures remaining a few degrees above normal, will continue through this period, resulting in widespread Minor and locally Moderate HeatRisk. An anomalously strong ridge will then build across western CONUS going through the middle portions of the week, with mid-level heights building to around 591-594 dam across the region. Temperatures will then soar to well-above normal levels, with Major HeatRisk developing Wednesday and expanding in coverage across the region Thursday and Friday. As a result, Excessive Heat Watches are now in effect Wednesday-Friday to account for increasing heat levels. Record highs may also be challenged during this period, with the current Thursday forecasted high for Phoenix set to break the daily record high. General probabilities of 110+ (115+) will peak around 40-70% (5-15%) across the lower deserts during this period. The decision to extend the Excessive Heat Watch through Friday is a result of recent ensemble model trends, where previous runs had a more potent and quicker moving troughing feature from Baja into the region. However, latest guidance shows a weaker and slower moving trough, thus extending the residence time of the intense ridge across the Desert Southwest through Friday. Looking through the weekend, this aforementioned trough will weaken the positive height anomalies some across the region, resulting in temperatures cooling a few degrees. Ensemble clustering shows little variance through Saturday, thus high confidence in impacts from the trough being some moisture advection resulting in some enhanced PWAT levels 125-175% of normal (~0.75") going into early next week. Thus, there remains low (at most 10-15%) chances for higher terrain convection (peaking Friday and Saturday), but these chances continue to trend downward due to the weaker trough scenario. Greater spread in the ensembles are observed Sunday onward, where the strongest signal at this point is the ridge axis sliding eastward of the region, with another trough potentially developing in the eastern Pacific around 30-35N. This scenario would result in continued above normal temperatures, but little to no extreme heat potential through early next week. && .AVIATION...Updated at 0510Z. South-Central Arizona including KPHX, KIWA, KSDL, KDVT; and Southeast California/Southwest Arizona including KIPL and KBLH: No significant weather issues will exist through Monday night under gradually increasing high cirrus decks. Across the Phoenix metro, wind behavior and timing of typical wind shifts will follow a near persistence forecast including occasional westerly gusts 15-20kt during late afternoon/early evening. In SE California, winds will generally back to a SE direction Monday morning, then veer towards a SW component by early evening. && .FIRE WEATHER... Little to no change in the weather pattern will keep seasonably dry and hot conditions in place through Tuesday. Expect lower desert highs between 100 and 105 degrees, or 3-5 degrees above average each day. MinRH values will continue to run between 5-10% across the majority of the area each day, while overnight recoveries will continue to range from poor to fair at around 25-40% over the eastern districts to 35-50% over the western districts. Winds will remain fairly light following diurnal tendencies with periodic afternoon gusts of 15-20 mph. The latter half of the week will see even hotter temperatures with potential for highs around 110 degrees Wednesday through Friday over portions of the lower deserts. There will also eventually be a slight improvement in humidities by next weekend along with a low end chance (10-15%) of some isolated thunderstorms over the Arizona higher terrain. && .CLIMATE... Record high temperatures: Date Phoenix Yuma El Centro ---- ------- ---- --------- June 5 113 in 2016 115 in 1957 114 in 2016 June 6 111 in 2016 114 in 1928 113 in 2002 June 7 115 in 1985 116 in 1985 113 in 1985 && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Watch from Wednesday morning through Friday evening for AZZ530>556-559>562. CA...Excessive Heat Watch from Wednesday morning through Friday evening for CAZ561-563-566-567-569-570. && $$ DISCUSSION...Young AVIATION...18 FIRE WEATHER...Young/Kuhlman CLIMATE...18