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.


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.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