Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/08/21

Area Forecast Discussion

National Weather Service Phoenix AZ

 405 PM MST Tue Sep 7 2021

.UPDATE...
Updated Aviation

&&

.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...
An expansive and anomalous anticyclone across the Great Basin will
gradually slide east and south over the next several days. Latest
water vapor imagery reveals very little moisture aloft within the
anticyclonic circulation. Although the largest positive height
anomalies will generally slide to our east, an extended period of
above normal temperatures is anticipated.

In the short-term, a few weak subsidence inversions are evident in
the most recent ACARS soundings out of KPHX, yielding a large area
of convective inhibition. Latest HREF confirms convective activity
today will be relegated to far southern Arizona. Chances are
slightly better Wednesday, as the CAMs have consistently have shown
a signal for isolated storms across far southern Maricopa County.

Main forecast concern will be the potential for Excessive Heat,
particularly across portions of the Phoenix area beginning Thursday.
Although forecast temperatures are right on the cusp of high heat
risk, trends over the past few days suggest an Excessive Heat Watch
is warranted. There is also a 25% chance high temperatures in
Phoenix could reach 110 degrees, which is the record for the day.

&&

.PREVIOUS DISCUSSION...
Models mostly agree the upper level ridge will shift eastward
through Friday before stalling out somewhere across our region. The
ridge should also weaken slightly, but heights and thicknesses aloft
generally remain stable across our region through the weekend
meaning very little change in the air mass. NBM probabilities of
reaching 110 degrees increases over the weekend for Phoenix and Yuma
(topping out at 40% and 50% respectively on Sunday) likely due to
even further loss of boundary layer moisture and lowering surface
dew points. Any highs reaching or exceeding 110 degrees in Phoenix
this time of year would be near record territory. Model ensembles
eventually point toward the ridge weakening further and becoming
more elongated at some point during the first half of next week.
This would yield some gradual cooling across the region, but likely
keep dry conditions in place.

&&

.AVIATION...Updated at 2305Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT; and
Southeast California/Southwest Arizona including KIPL and KBLH:

Little to no weather impacts are expected through Wednesday night
under mostly clear skies. Winds at KPHX may take somewhat longer to
switch to easterly overnight, then may exhibit a prolonged period of
light and variable character late morning through mid afternoon
Wedneday before settling on a W/SW component. Winds at SE California
terminals will follow typical diurnal patterns experienced the past
couple days. Wind speeds around the entire region should remain
below 12 kt.

&&

.FIRE WEATHER...
Thursday through Monday:
Strong high pressure will dominate over the Southwestern U.S. 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 approaching 110 degrees.
Min RH levels will range from 15-25% through Saturday with readings
dropping to 10-20% starting Sunday, while max RHs generally range
from 35-55% (locally higher). Winds will overall remain light
through the period while following typical diurnal patterns.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Watch from Thursday morning through Thursday
     evening for AZZ537-540>544-546-548>551.

CA...Excessive Heat Warning until 8 PM PDT Thursday for CAZ561-570.

&&

$$

DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Kuhlman
AVIATION...18
FIRE WEATHER...Kuhlman