Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/12/20

Area Forecast Discussion
National Weather Service Phoenix AZ
520 PM MST Sat Apr 11 2020 .UPDATE...Updated Aviation Discussion. && .SYNOPSIS... Scattered showers and a few thunderstorms will decrease in coverage late this afternoon and end tonight as our lingering low pressure system pushes into far southeast Arizona. After a brief break tonight into Sunday morning, another disturbance will bring additional rain chances to northern and eastern Arizona on Sunday and Monday, with a slight chance of showers in the Phoenix metro on Monday. Southeast California and southwest Arizona will remain dry on Sunday and Monday, with south central Arizona beginning to dry out on Tuesday with highs climbing above normal by Thursday. && .DISCUSSION... Isolated to scattered showers and even a couple thunderstorms are ongoing across south central Arizona this afternoon as the cutoff mid-to-upper level low along the Mexico-Pima County border is finally ejecting to the southeast. Showers are also occurring over higher terrain locations in La Paz and Yuma Counties, but dry air is rapidly moving in from the west to prevent showers at lower elevations. This drying trend will continue to sweep eastward over the next couple of hours to end convective chances over the Phoenix metro by late afternoon, with aircraft soundings into KPHX beginning to show this drying trend as well that is keeping our instability in check despite favorable low-level and mid-level lapse rates. As previously expected, the best chances for deeper thunderstorm activity across the Phoenix metro has passed with only showers expected over the next couple of hours aside from the far southeast portion of the metro where one thunderstorm south of Florence is dissipating. SPC Mesoanalysis is also showing that we have lost our instability, so we continue to have very little confidence in any convection pushing off the Rim into the Valley late this afternoon and early evening. Any convection that does cross into far northern Maricopa County should dissipate quickly as it moves into lower elevations early this evening. The aforementioned low will continue to push southeast into Mexico this evening to set up dry northwest flow across the region overnight into tomorrow. Global and hi-res model ensembles continue to show a broad shortwave trough at midlevels moving into northern Arizona by late Sunday afternoon, triggering another round of showers and isolated thunderstorms just north of the region along a weak dissipating front. However, enhanced upper- level divergence interacting with remnant moisture aloft late in the overnight hours into the day on Monday should be enough to help trigger shower activity further south into at least the Phoenix metro. A few isolated thunderstorms will also be possible on Monday afternoon, with the best chances over higher terrain areas north and east of Phoenix as model soundings suggest there will be much less instability than there was with today`s storm system. Temperatures over the lower deserts will also continue to remain several degrees below normal on Sunday and Monday with highs in the upper 70s and lows in the mid 50s. A significant warming and drying trend will begin on Tuesday or Wednesday and continue through at least Thursday as northwest flow and then more zonal flow aloft persists over the region behind the departing trough. Temperatures should finally warm back up to near seasonal normals on Wednesday and above normal on Thursday as highs climb up into the mid to upper 80s. Forecast uncertainty is relatively high beyond Thursday as the global model ensembles are split between zonal flow continuing or another cutoff low splitting off of yet another shortwave dropping down from Alberta. For now, we have stuck with temperatures dropping a few degrees for Friday into the weekend back to seasonal normals with dry conditions, though a plurality (but not a majority) of ECM and GEFS members favor troughing suggesting temperatures will be below normal with some potential for rainfall. && .AVIATION...Updated at 0020Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Shower activity across the metro this afternoon will continue to taper off as we head into the early evening hours. Can`t rule out an isolated vicinity shower near the terminals this evening, but most shower activity is now diminishing. Winds at this hour have been variable as a result of various boundaries and showers across Phoenix. Winds are expected to become westerly/southwesterly again at the terminals early this evening, lasting into the late evening. Winds transition to the east later tonight with speeds remaining below 8 kts. Winds pick up out of the west by early tomorrow afternoon with some gusts into the teens possible. Otherwise, SCT- BKN clouds around 6 to 8 kft should scatter out some this evening with FEW-SCT low to mid level decks remaining throughout the TAF period. Southeast California/Southwest Arizona including KIPL and KBLH: Satellite imagery this afternoon showed mostly clear skies across southeast California with only some cumulus remaining. Expect clear to mostly clear skies to continue through the next 24 hours at the terminals. Winds will favor the west at KIPL while winds favor the south at KBLH. Winds become breezy by tomorrow afternoon with some gusts into the low 20s possible. && .FIRE WEATHER... Monday through Friday: A weak upper level disturbance moving across the northern half of Arizona on Monday will bring scattered showers mainly across the Arizona high country before a drying trend takes place during the middle part of next week. Below normal temperatures early in the period will warm to around normal by Thursday. Min RH values between 25-30% are expected Monday, lowering beginning Tuesday to below 15% each day. Winds will generally remain fairly light through the period, but with daytime breeziness likely on most days. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Hopper/Kuhlman AVIATION...Smith FIRE WEATHER...Kuhlman