Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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061 FXUS65 KPSR 211035 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 335 AM MST Sat Sep 21 2024 .SYNOPSIS... An unsettled weather pattern will calm going through today, with quieter weather conditions moving forward through this upcoming week. Cooler than normal temperatures will trend warmer to above normal readings by early next week. && .DISCUSSION... A potent upper level low centered over western Arizona is continuing to spark some low-topped showers and storms across the eastern portions of the region, now primarily east of the Phoenix metro. Otherwise, dry air, as seen in WV imagery, is preventing more widespread activity, as the main activity is along the frontal boundary and near the cold core of the upper low. As this upper low continue to track eastward across the northern portions of the forecast area, shower and storm coverage is expected to likewise shift eastward, with limited convective potential during the daytime hours across northern Maricopa and central Gila Counties. Due to the anomalously cold upper level low overhead, temperatures will continue to remain below normal, with today expected to be the coolest day across southcentral Arizona over the next week. As the negative height anomalies traverse eastward in association with this upper low going into tomorrow, a quick response in warming temperatures will occur, as mid-level heights build in from the west. However, general longwave troughing will continue to persist across TX, NM, and even into eastern AZ going into early next week, resulting in temperatures only warming to a few degrees above normal across the region. High amplitude ridging in association with strong positive height anomalies will develop across the Pacific Northwest and into the Intermountain West early in the week, and persisting into the middle portions of the week. A weak shortwave riding along the eastern periphery of this ridge will keep this longwave troughing persisting into the middle of next week. Ensembles remain in good agreement with this general pattern during this period. Stronger positive height anomalies are expected to move into the Desert Southwest going into the latter portions of next week, as the main ridge axis sets up over Arizona. However, temperatures will remain just a few degrees above normal as the strongest anomalies remain well to the north, as the aforementioned longwave troughing across the Southern Plains continues to persist. Another strong trough originating from the Gulf of Alaska will also begin to impinge on the Pacific Northwest as well at this point, but isn`t expected to have any influence on any potential changes to the weather pattern here locally going into next weekend. Ensembles show a bit more divergence in the weather pattern, especially in regards to the persist troughing across central CONUS going through the end of the week. However, weak ridging is expected to persist across the region, keeping dry conditions and above normal temperatures across the region going into next weekend. && .AVIATION...Updated at 0554Z. South Central Arizona including KPHX, KIWA, KSDL, and KDVT: VCSH with potential brief -SHRA impacts is anticipated now through 8Z at the latest tonight. SCT to BKN clouds down to 7-8K ft is expected during this time period, with clearing thereafter. Winds will also shift S-SE during this time and prevail through the rest of the morning. There is another low chance (10%) for VCSH/VCTS Saturday morning, around the 15Z timeframe, but any activity may stay just north of the metro area. Confidence and probability is too low to include this in the TAF. An early W wind shift is expected Saturday, as early as 15-16Z. Wind speeds will remain light through the TAF period, mostly aob 8 kts. Southeast California/Southwest Arizona including KIPL and KBLH: No major weather concerns should exist through Saturday under periods of mid/high cloud deck tonight, then followed by mostly clear skies. SHRA in the region of KBLH, but outside the 10sm radius, may continue through 9-10Z in the region before fully dissipating. Current N winds at KBLH are expected to slowly turn counter-clockwise through the next few hours before becoming VRB. KIPL will favor a W winds tonight before also becoming VRB. VRB wind conditions are then expected at both terminals for much of Saturday. && .FIRE WEATHER... Some isolated shower and storm activity may persist into the morning hours across the eastern districts, but will result in only brief rain and low CWR`s (generally less than 10%). Otherwise, a drier and cooler airmass encompassing the region will result in below normal temperatures through today. More traditional diurnal winds patterns will encompass the region over the next several days. MinRH`s will hover around 15-30% region- wide through today, with some slight drying across the region starting tomorrow, with MinRH`s more in the 10-20% range by the beginning of next week and extending into the middle of next week. Overnight RH recoveries will be fair to good across the region through tomorrow morning, before degrading to generally fair to poor in spots going through the middle of next week. Warming temperatures to above normal are expected to develop tomorrow and persist through most of next week. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Young AVIATION...Benedict FIRE WEATHER...Young