Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/07/21

Area Forecast Discussion
National Weather Service Phoenix AZ
512 PM MST Mon Sep 6 2021 .UPDATE...Updated 00Z Aviation Discussion. && .SYNOPSIS... Strong high pressure aloft will be the predominant weather feature across the Southwestern U.S. this week providing above normal temperatures for much of the region. Generally dry conditions will also prevail despite somewhat higher humidity levels, though slight chances for storms may become possible later this week across southeast California and the Arizona higher terrain. Daily high temperatures will mostly range from 105 to 108 degrees across the Arizona lower deserts to a couple of degrees warmer across southeast California and southwest Arizona. && .DISCUSSION... RAP streamlines depict a large anticyclone centered across the Great Basin. Abundant dry air aloft is also evident on water vapor imagery, though conditions remain somewhat moist at the surface, particularly across portions of southeastern California. In the Imperial Valley, dewpoints in the mid 70s are resulting in heat indices as high as 115 deg. Meanwhile, afternoon ACARS soundings out of KPHX reveal a warm and dry layer around 700 mb, which is yielding a considerable amount of convective inhibition. HREF confirms conditions will remain quite unfavorable for Monsoon thunderstorm activity for the remainder of today. The aforementioned anticyclone will remain the predominant weather feature through the week. GEFS/ECWMF/CMC ensemble suites remain in good agreement the high will shift eastward and then southward through the week. The models also indicate the strongest height anomalies will remain to our north and east. Main impact across the Desert Southwest will be a warming trend with temperatures likely peaking mid-late week. Latest NBM guidance puts the Phoenix Metro area a bit below criteria for an Excessive Heat Watch Wednesday/Thursday, though if trends continue, a Watch or Warning may ultimately be needed. For Wednesday and Thursday, there is currently a 25-35 percent chance the high temperature will reach or exceed 108-109 deg in Phoenix, which roughly corresponds to a high heat risk this time of year. Latest GEFS/ECMWF ensemble temperature distributions depict a reasonable amount of uncertainty, and it is still conceivable the record high temperature of 110 deg (both days) could even be reached. Uncertainty increases more Friday through Monday, though temperatures will likely remain above average. With relatively dry and warm air circulating around the ridge, conditions will remain unfavorable for Monsoon storms at least into the weekend. The only exceptions will be across the higher terrain of Gila County and extreme southern Maricopa County. Only a handful of GEFS/ECMWF ensemble members suggest precipitation will reach the lower deserts of south-central Arizona. Latest ECMWF ensembles suggest the best chance of precipitation may actually be along the Colorado River Valley Thursday-Saturday as GOC moisture is pulled northward. && .AVIATION...Updated at 0010Z South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Diurnal wind tendencies are favored through the TAF period at most terminals with speeds mainly 8 kts or less. At KPHX, winds are expected to remain westerly or southwesterly through the next 24 hours with a slight uptick in speed up to 12 kts tonight following a gulf surge. There are indications winds may still try to shift east, or become variable, around 11-12Z, but the probability is currently too low to include in the TAF. Skies will remain clear outside distant afternoon cumulus. Southeast California/Southwest Arizona including KIPL and KBLH: Winds will favor the south at KBLH and east to south at KIPL through the TAF period, with periods of variability in the morning. Speeds will mostly be 8 kts or less, besides typical afternoon gusts and a brief uptick to 10-15 kts tonight following a southerly gulf surge. Skies will remain mostly clear. && .FIRE WEATHER... Wednesday through Sunday: Strong high pressure will dominate over the Great Basin into the Desert Southwest late this week into the weekend providing generally dry conditions and above normal temperatures. Chances for showers and thunderstorms will be very limited through the period, especially over the Arizona lower deserts where chances will be less than 5%. High temperatures are likely to run a few degrees above normal throughout the period with some lower desert areas potentially seeing a return of 110 degree readings. Min RH levels will mostly range from 15-25% through the forecast period, while max RHs generally range from 40-60% (locally higher). Apart from thunderstorms, strong wind events are not anticipated. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...Excessive Heat Warning from 10 AM Tuesday to 8 PM PDT Wednesday for CAZ561-570. && $$ DISCUSSION...Hirsch AVIATION...Benedict FIRE WEATHER...Kuhlman