Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 05/19/21

Area Forecast Discussion
National Weather Service Phoenix AZ
445 PM MST Tue May 18 2021 .UPDATE...Aviation Discussion. && .SYNOPSIS... A departing low pressure system will bring a slight chance of showers and isolated thunderstorms over central and eastern Arizona today. These showers will result in minimal rainfall, with gusty winds being a more likely impact for the high country and possibly parts of Phoenix. Temperatures will rebound to near normal today and then above the seasonal average tomorrow. However, another weather system will arrive Thursday into Friday, resulting in breezy conditions and cooler weather. && .SYNOPSIS... The upper air analysis now shows northerly cyclonic flow aloft at H5 across AZ and the region on the west flank of a closed low pressure system over N NM. METSAT imagery shows the large cloud shield cyclonic circulation northeast of the region along with convective CU developing across the Mogollon Rim. WV imagery depicts elevated moisture and vort max disturbances rotating around the periphery of the low. Current radar reveals very light returns associated with some sprinkle showers and possibly virga although in a semi-organized pattern. Current ACARs soundings show PW recently increasing to upwards of 0.77` and slightly elevated moisture in the upper-mid levels near 600 mb with low-end CAPE of 310-421 j/kg, with DCAPE near 875 j/kg. HREF family members agree on fairly isolated convection for S. Gila Cty & Mogollon rim as the next PVA disturbance rotates and pivots through the region. The outlier is the HRW FV3 which is a little more bullish on the prospects for convection/showers with a bit better coverage. The rotating vort lobe(s) will produce sufficient vertical lift and dynamics to provide a slight to fair chance of scattered to isolated showers and a thunderstorm over the high terrain areas, with only a slight chance for NE-E Maricopa Cty and the N-NE-E Phoenix valley this afternoon and early evening. Although there is a slightly better chance for a few storm outflows to push into the Phoenix Valley his afternoon or evening from the north and east with a gust potential of about 25-35 mph (15-30% chance). This would be the main impacts of these storms along with an outside chance of lightning. Any storms are not expected to produce any significant QPF due to insufficient forecast moisture/PW in the column. As the low pressure system exits into the southern plains Wednesday, shortwave ridging will temporarily build back into the SW Conus allowing temperatures to warm back above the seasonal normal. By Wednesday, NBM temperature probabilities show about a 75% chance of reaching 100 F or higher. Beyond, Wednesday, another weather system will impact the region. Ensemble guidance is now in good agreement that a closed low will develop over the Great Basin. WPC clusters show that there is relatively minimal variation in the big picture through day 5, with the main uncertainty relating to how far to the southwest the negative height anomalies will extend. These differences will affect the magnitude of the breezy conditions that develop as well as the degree of cooling. In either case, the Wednesday through Friday period will likely be the windiest. Temperatures will be likely be the coolest Saturday and Sunday. Rain remains very unlikely. Ridging and rapidly warming temperatures are likely to return thereafter. && .AVIATION...Updated at 2345Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: The potential for thunderstorms/showers and any related aviation impacts continues to dwindle as convection has failed to maintain south of the Mogollon Rim. There is a 10% chance or less for storms or sudden wind shifts from outflow winds this evening. If these do occur, the best timing is from now through 03Z and would most likely cause an early easterly wind shift for KDVT, KSDL and/or KIWA. Otherwise, westerly winds gusting up to 20-25 kts are anticipated to last through sunset. The overnight easterly winds should begin around 10Z tonight and last until late Wednesday morning/early afternoon when the westerly winds will resume with gusts once again reaching 20-25 kts. There may be periodic moments of LLWS for the TAF sites late tonight but confidence in this reaching TAF thresholds is too low at this time. Southeast California/Southwest Arizona including KIPL and KBLH: Winds will become the primary aviation weather concern by tomorrow afternoon. Until then, westerly winds will continue at KIPL while southerly winds continue at KBLH. Both terminals could see some afternoon and late evening gusts of 20-25 kts. For tomorrow, the westerly winds will strengthen at KIPL after a brief period of morning easterly/variable winds. Gusts are anticipated to reach 25 kts and occasionally 30-35 kts. At KBLH, the southerly winds will become south-southwesterly by Wednesday afternoon with speeds reaching 20-25 kts and gusting to 30-38 kts. Areas of blowing dust could reduce surface visibilities while lofted dust could create slantwise visibility issues. && .FIRE WEATHER... Friday through Tuesday: A strong weather disturbance will approach the region during the latter half of the week pulling temperatures back below normal and leading to breezy winds. The breeziest conditions will likely occur Friday afternoon with gusts near 20-28 mph over ridge tops and exposed areas. With very dry fuels, an elevated fire danger is possible Friday afternoon, with some threat of critical thresholds being met locally. Min RH levels will stay near 5-10% through the period. Overnight recovery will be poor to fair in a 25-50% range initially, decreasing to 15-35% over the weekend. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...Wind Advisory from 3 PM to 11 PM PDT Wednesday for CAZ560-562- 563-566. && $$ DISCUSSION...Sawtelle/Hodges AVIATION...AD FIRE WEATHER...Sawtelle/Hodges