Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/06/20

Area Forecast Discussion
National Weather Service Phoenix AZ
428 PM MST Sat Dec 5 2020 .UPDATE...Updated aviation discussion. && .SYNOPSIS...A warming trend will continue through Tuesday as high pressure builds across the Desert Southwest. High temperatures in the lower deserts may approach the 80 degree mark Tuesday. A low pressure system will likely move through the region late next week, bringing a slight chance of precipitation and a return to cooler conditions. && .DISCUSSION... An anomalously strong upper level high pressure area remains centered over the northern Great Basin Region with an elongated axis of above normal heights extending southwest towards southern California. The low pressure center that brought the cooler air to the region several days ago has now moved into west Texas and continues to slowly push eastwards out of the area. A weak low level stable layer remains near the surface but ACARS soundings reveal that it is slowly moderating, with 850 mb temperatures about 3 degrees C warmer than yesterday at this time. Easterly flow throughout the depth of the troposphere remains but has weakened considerably compared to the last few days. With the slight warming of the lower atmosphere, high temperatures will climb a few degrees above what was noted yesterday, and should top out near 70 degrees in the lower deserts under continued sunny skies. The models remain in good agreement depicting the aforementioned ridge predominating across the intermountain West the next few days. This will yield a gradual increase in thicknesses along with a warming trend. Latest NBM multi-model ensemble continues to indicate roughly a 30 percent chance of reaching the 80 degree mark in Phoenix on Tuesday. Meanwhile, GEFS/ECMWF ensemble means show a Pacific PVD will fracture Sunday across the Great Basin before dropping due south into California Monday and retrograding off the California Coast Tuesday. In terms of sensible weather, the main impact across the Desert Southwest will initially be an increase in high clouds Monday, particularly across southeastern California. All model clusters indicate the low off the California coast will meander before getting picked up by another eastern Pacific trough and eventually merging with it. This progression is unlikely to allow for deep moisture or favorable dynamics to move into the forecast area, but instead will result in more of a glancing blow with any deep moisture and associated dynamics remaining well to the southeast. Although a slight chance of showers remains, the most likely outcome is that the dry streak will continue across the Phoenix CWA, especially for locations further to the west. Uncertainty increases considerably late in the week behind the departing closed low. WPC cluster analysis shows large spread in the strength and amplitude of the north Pacific ridge and the corresponding downstream potential trough over the western US region. The majority of the Canadian ensemble shows a SW-NE oriented area of high pressure over the Pacific Northwest region, while the GFS ensemble shows a more N-S orientation which allows for the cooler air to spill into the desert southwest. The ECMWF ensemble is split between these two general solutions. Needless to say, confidence is not high in any particular outcome at this time. && .AVIATION...Updated at 2330Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns expected through the TAF period. Light, diurnal winds will prevail under generally clear skies. A few high clouds aoa 25 kft will start to move in overnight from the west, mostly over KBLH & KIPL this period. Wind speeds at all sites should remain near 6 kts or less. Due to this, extended periods of light/variable winds are likely to occur as well. && .FIRE WEATHER... Monday through Friday: High pressure will predominate early this week, resulting in light winds, above normal temperatures and seasonably dry conditions. A low pressure will likely move through the region late in the week, bringing cooler conditions and an increase in moisture. However, there is only a slight chance of showers Thursday and Friday, mainly concentrated across the higher terrain of southern and eastern Arizona. Minimum humidities will generally be in the 10-20% range through Wednesday with overnight recoveries in the 25-45% range. Higher RH values are likely Thursday and Friday. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Hodges/Hirsch AVIATION...Rogers/Feldkircher/Kuhlman FIRE WEATHER...Hirsch