Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/22/20

Area Forecast Discussion
National Weather Service Phoenix AZ
615 PM MST Mon Sep 21 2020 .UPDATE...Updated Aviation discussion. && .SYNOPSIS... A weak slow moving disturbance will bring occasional scattered to broken clouds and a slight chances of widely isolated light showers and sprinkles through Tuesday. Drier conditions return for the second half of the week. High temperatures will fluctuate slightly, but remain at least several degrees above normal through the week. && .DISCUSSION... The modest UL trough axis remains negatively tilted across far NW MX and the AZ borderland with a cold air trough now centered over NE AZ at H5. Slightly stronger cyclonic flow ahead of the trough was shifting into SW AZ as it slowly shifts east. A thin zonal H3 60 kt jet streak was slicing across S-central AZ just ahead of a mid-level vort max. Early afternoon/midday ACARS soundings maintained modest mid-level CAPE, BL CIN and PWs near 0.95-1.0". Models continue to maintain the elevated PW anomaly and very weak and spotty mean CAPE through Tuesday. Low and mid-level GOES WV and IR continued to show the slightly elevated moisture axis with sct-bkn ACCAS across S-S- Central AZ and the borderland slowly drifting northwest in advance of the low. Early afternoon local radar shows the resulting isolated light showers and sprinkles continuing mostly across S-Central-SW AZ including the western half of Maricopa Cty. The weak and relatively/mostly dry low pressure will shift slightly east as it loiters over SW and S-central AZ through Tuesday evening and continue to bring slight chances of widely isolated, mostly light showers and sprinkles/virga and isolated moderate showers across the lower deserts and Phoenix. For tonight and Tuesday the best slight chances will be for Maricopa county westward, including Phoenix. The only precipitation-related impacts might be some locally breezy conditions near a heavier shower, due to some locally elevated forecast DCAPE, or the very slightest chance of a lightning strike from a very isolated renegade thunderstorm. Downpours and flooding are currently not expected with QPF generally remaining at little to none. The day 3 and 4 NCEP/WPC 500 mb heights clusters and ensembles are in good agreement on a progressive ridge of high pressure building across S CA and the SW US through the Central Plains/US on Wednesday and Thursday. By Friday the ridge flattens in response to a progressive low and a broad troughing-zonal jet stream combo to the north. Drier and slightly warmer conditions are on tap for the second half of the week. With only a couple degrees of warming, highs will remain in the low-mid 100s through the end of the week. A gradual cooling trend for overnight lows begins in the middle of this week with overnight reading bottoming out in the upper 60s for the outskirts of Phoenix and lower deserts and the mid 70s for the city. The weekend favors continued dry conditions with dry northwesterly flow aloft and a fair chance of high pressure building across the West Coast Sunday and Monday. Another stint of briefly warmer temperature are possible starting late this weekend, although some 7-day H5 height cluster uncertainty remains on the east-west position of the ridge. && .AVIATION...Updated at 0115Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Mid clouds are expected to thicken once again tonight ahead of a weak low pressure across southern California. Isolated showers will likely develop across central Arizona around 07Z-09Z with the threat continuing through mid-morning. If a shower does materialize at any of the TAF sites, it may be strong enough to briefly wet the runways. Meanwhile, diurnal winds will generally prevail at all TAF sites. Improving conditions are expected Tuesday afternoon as the aforementioned low pressure system lifts out into northern Arizona. Southeast California/Southwest Arizona including KIPL and KBLH: Isolated showers near KBLH will dissipate early this evening, though some mid clouds may persist overnight. Otherwise, diurnal winds with mostly clear skies can be expected through Tuesday. && .FIRE WEATHER... Thursday through Monday: A dry weather pattern will dominate the period with highs remaining several degrees above normal in the low to mid 100s. Min RH values near 10-14% will fall to near 10% on Sunday and Monday. Max RH near 25-40% most places will gradually dry to the low to mid 20s by Sunday across the lower deserts and 25-40% for the higher elevations. Winds will be mostly light and favor normal diurnal patterns with typical afternoon breeziness. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Sawtelle AVIATION...Hirsch FIRE WEATHER...Sawtelle/Benedict