Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 11/24/21

Area Forecast Discussion

National Weather Service Phoenix AZ

 449 PM MST Tue Nov 23 2021

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
A relatively weak low pressure system passing through
the region today into Wednesday will bring chances for light rain
across south-central Arizona and the higher terrain north and
east of Phoenix mainly this afternoon through early Wednesday
morning. A secondary system on Wednesday will produce drying
conditions and cooler temperatures on Wednesday, or near normal
for this time of year. Breezy to windy conditions are also
likely across southeast California and southwest Arizona on
Wednesday and then in Phoenix, the lower deserts and high country
on Thursday. High pressure building back into the region late in
the week should bring a minor warming trend, likely leading to
high temperatures back into the mid to upper 70s for Friday and
Saturday.

&&

DISCUSSION...
The upper air analysis and WV imagery depicts very moist SW flow
aloft ahead of a low pressure circulation and a series of PVA
anomalies extending from just offshore of N Baja, and an upper
level trough across S-Cent CA. Early afternoon GOES IR imagery
showed widespread cloudy conditions with a large cloud shield with
and ahead of the low pressure system. There was also a large area
of elevated mean RH well above 70% from H7-H5 on the SPC 700 mb
analysis moving east through SW to cent AZ. The PW analysis
depicted a tongue of elevated PW extending NEward from a >0.8"
maxima over SW AZ with the latest Phx ACARs showing a PW of 0.87".
Early afternoon radar revealed a large area of scattered to
isolated sprinkles, light rain and virga with very little if any
precip reaching the sfc due to the largely dry boundary and
subcloud layer below H7 revealed on Phx ACARs.

The weak low pressure system will eject through the region today and
tonight bringing up to a 20-30% chance of light rain and showers
across Phoenix and the lower deserts and the N to E high terrain
areas this afternoon and tonight. All models agree on very
subdued QPF ranging from a hundredth of an in. around Phoenix to
less than 0.1-0.2" for the high country.

Models and ensembles also agree on a secondary trough dropping
through the western CWA tomorrow/Wed which will produce very breezy
to windy conditions across parts of SE CA, the Lower CO River Valley
and SW AZ on Wednesday and Thu. The breezy to windy conditions will
then spread east to Phoenix and the lower deserts and the E high
terrain on Thu. The strongest wind gusts will likely reach 35-50
mph range and impact fairly limited areas, mainly across the
highest ridge tops by Wed afternoon and into the evening.
Windspeed trends in future model cycles will be closely monitored
to determine whether advisory level winds become widespread
enough to warrant possible wind advisories.

Dryer and slightly cooler conditions also begin tomorrow with
temperatures falling to near normal, in the low to mid 70s for the
highs by Wed. Lows in the mid 40s in the NW CWA deserts on Wed
morning, and the upper 40s around Phoenix by Fri morning (two
mornings later) are also likely as a result of the CAA associated
with these systems.

For late this week models agree on forming a fairly cut-off low over
NW MX by Thu or Fri as a ridge of high pressure builds in from
the northwest. Ensembles and clusters analysis shows a bit of
uncertainty on the N-NW MX low`s position and precipitation
chances for the weekend. Day 4/Sat QPF depicted some noticeable
QPF in cluster #3, with 30% of all members, associated with that
low and more than 50% GFS ensemble members. For Day 5/Sun,
cluster #5 held out some hope for some limited QPF across the
region however it had less than 20% of the members with most
clusters supporting a significantly filled/weakened low and dry
conditions.

&&

.AVIATION...Updated at 2350Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
A passing weather system is producing low-end aviation weather
issues with some uncertainty regarding this TAF package. For
winds, indications suggest a prevailing W to NW direction for the
next two to four hours before the easterly overnight winds prevail
sometime 05z. However, isolated showers and/or virga will create
periods of isolated erratic wind directions (periods of
westerly/northerly/easterly) through this evening. Therefore,
variable winds at 5 kts could end up the predominate wind this
evening. Speeds will remain relatively light between 5-8 kts most
of the time but cannot rule out an isolated gust of 20-25 kts near
any showers or virga. Chances for showers within the terminal area
are still too low to mention in the TAFs (20% chance this
evening). Lower ceilings will continue with an OVC deck slowly
dropping to FL090-120 for much of the next 12 to 18 hours with
some FEW or SCT decks between 060-090. For tomorrow, ceilings will
not likely lift much above 100-120 until the later afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:
There are no major aviation weather concerns for this evening or
tonight with persistent conditions. However, winds will become
northerly at both terminals late Wednesday morning/early afternoon
while wind speeds increase. For Wednesday afternoon, KIPL wind
speeds are expected to reach 10-14 kts while gusting at 20-24 kts.
Stronger winds of 15-20 kts and gusts of 25-30 kts are expected at
KBLH. These stronger winds may lead to reduced surface visibility
from blowing dust and/or slantwise visibility issues once dust
becomes lofted.

&&

.FIRE WEATHER...
Thursday through Monday:
High pressure will generally dominate across the region through
the period, but with a stalled out low pressure system positioned
just to the south through the weekend. This will promote dry
conditions through at least Friday with only minimal chances for
some light rain this weekend if the system to our south shifts
close enough to our region (model uncertainty remains). Winds will
start out fairly breezy on Thursday with gusts to around 20 mph
before mostly light winds are anticipated through the rest of the
period. Min RH values are likely to fall between 10-20% for most
locations each day, to 20-30% across the eastern Arizona high
terrain.

&&

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

$$

DISCUSSION...Sawtelle
AVIATION...12
FIRE WEATHER...Kuhlman