Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/17/20

Area Forecast Discussion...Updated

National Weather Service Phoenix AZ

 445 PM MST Wed Dec 16 2020

.UPDATE...Updated aviation discussion.

&&

.SYNOPSIS...
A slow warming trend will allow for high temperatures to push
above the seasonal average this weekend through early next week.
However, mornings will remain cold in the 30s to low 40s through
the next several days with some outlying lower desert areas still
flirting with freezing. A weather disturbance will bring cloudy
conditions Thursday and breezy northerly winds along the Lower
Colorado River Valley Friday. No precipitation is expected through
the next 7 days.

&&

.DISCUSSION...
The Desert Southwest remains under dry and stable northwest flow
this afternoon. Aircraft soundings in Phoenix show the low level
thermal profile has warmed 5-8C over the past 24 hours. This
should help this afternoon`s surface temperatures warm a few
degrees from yesterday, especially across the south-central AZ
deserts. Thursday morning`s lows will be slightly warmer as well,
but the dry conditions and clear skies will still support strong
radiational cooling and some of the typical cold valley spots will
still flirt with freezing; locations like northwest Pinal,
central Yuma, and central La Paz counties. Morning lows Thursday
through this weekend will remain relatively unchanged day to day,
with most communities, besides the aforementioned cold spots, in
the upper 30s to low 40s.

An upper low currently moving east just offshore of the PacNW is
expected to become an open wave upon moving inland tonight and
turn southeast. The wave will eventually pass through northern AZ
Thursday night. As a positively tilted shortwave, it will quickly
move east of the area by Friday night. Other than some light
rain/snow showers in northern AZ, this will be a relatively dry
system for most of AZ and southern CA. A rather thick shield of
mid and high clouds will stream in ahead of the trough axis during
the day Thursday. Would not be surprised to see some linear bands
of virga pass over the southern AZ and CA. The clouds should
clear quickly following the passage of the trough axis Thursday
evening/night. With the base of the trough passing over the area,
gradient winds aloft will increase, but is not expected to mix all
the way down to the lower desert floors given the strongest winds
pass over Thursday night. Though there may be some breezy
downsloping winds into the Imperial Valley from the west Thursday
evening followed by a breezy northerly wind down the Lower
Colorado River Valley during the day Friday.

There will be hardly any impact on temperatures with the
shortwave Thursday-Friday other than briefly delaying a more
distinct warming trend expected this weekend. Models suggest
another subtle shortwave trough glancing by to the northeast this
weekend, but overall ensemble trends support positive height
anomalies across much of the western CONUS through early next week
with a weak flow regime. As mentioned low temperatures will
remain relatively unchanged day to day due to dry conditions and
radiational cooling, but high temperatures will warm above
seasonal normals with most lower deserts returning to the 70s by
Sunday. Towards the middle of next week, ECMWF ensemble and GEFS
mean suggest the positive height anomalies will break down and
afternoon temperatures will return to seasonal levels. Still no
indication of when the next chance for rain will be.



&&

.AVIATION...Updated at 2345Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

No aviation concerns are expected over the next 24 hours across the
lower deserts. In the greater Phoenix area, expect light winds
tonight into Thursday; light west wind to shift to the east in the
04-05z time window. Light east wind will persist and become a bit
more southeast later Thursday morning as low level flow backs ahead
of an approaching weather system. Winds Thursday afternoon likely to
be either light/variable or light southeast with less chance of wind
shifting to a westerly component. Skies tonight generally clear with
some cirrus approaching by early Thursday morning; increasing cirrus
during the day becoming mostly BKN with bases lowering to around
15k feet by midday.

Southeast California/Southwest Arizona including KIPL and KBLH:

An approaching weather system from the west will lead to increasing
mainly high clouds later tonight into the day on Thursday. Look for
increasing cirrus decks with bases aoa 25kt this evening thickening
by Thursday morning becoming BKN-OVC (thin at times). Bases lowering
to around 15k by mid morning with clearing from the west during the
afternoon. Wind will be rather light; at KIPL they favor the west
with lots of light/variable and they will increase and swing to the
south or southwest during the afternoon Thursday. Light north winds
at KBLH tonight will become light variable after midnight and then
turn to the south up to 10kt later Thursday morning as the trof
approaches. Overall there are no aviation concerns at the terminals
over the next 24 hours.

&&

.FIRE WEATHER...
Friday through Tuesday: Near normal temperatures will persist
through the forecast period with a slow warming trend into the
weekend. A few clouds are anticipated Friday morning but with no
rain. High temperatures will increase from the mid 60s to the low
70s. RH maximums will be between 40-60% Friday falling to 30-50%
the rest of the period. RH minimums will be 20-30% Friday falling
to 10-20% the rest of the period. The lower RH values will be
found to the west.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...Benedict
AVIATION...CB
FIRE WEATHER...Hodges