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