Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/03/21

Area Forecast Discussion

National Weather Service Phoenix AZ

 502 PM MST Thu Sep 2 2021

.UPDATE...Aviation discussion update.

.SYNOPSIS...
Drier air will spread into the region the remainder of the week
resulting in reduced rainfall chances. Isolated storms will still be
possible over mountains of eastern Arizona, but little chance of
rain elsewhere. This drying trend will also bring warmer
temperatures to the region with readings gradually increasing to
near and slightly above normal levels. Thunderstorm activity may
return to the region next week.

&&

.DISCUSSION...
Increasing SW flow in the middle/upper troposphere was beginning to
introduce a drier atmospheric profile into the region per WV
satellite imagery. However, low level moisture remains abundant with
expansive 12-15 g/kg boundary layer mixing ratios, and pockets of
saturation resulting in a few lingering showers. However, in situ
aircraft soundings are showing the first vestiges of the drier
airmass starting to erode the thicker moisture. Given the residual
moisture superimposed with daytime upslope flow, additional isolated
showers are likely the remainder of the day. The general trend will
be towards a subsident regime, and rapid clearing should occur
shortly after sunset.

Over the next 72 hours, subtropical ridging centered over the
southern plains will split in response to northern stream jet energy
amplifying the Conus flow pattern and digging negative height
anomalies over the northern plains and Great Lakes. The western lobe
of high pressure should retrograde and intensify into a 594dm ridge
centered on southern CA/NV. This evolution will not only restrict
thunderstorm chances through drying, warming, and sinking of the
atmospheric column, but also spur a notable warming trend. Current
NBM official median forecasts bring readings slightly above normal
by early next week, and around moderate heat risk levels. Ensemble
spread is still rather wide, especially closer to the anti-cyclone
center through the western CWA where a 30-50% chance of readings
reaching 110F still exists. Probabilities of this type of heat in
the Phoenix metro is far lower (<10%), but still a reminder that
monsoon season and heat impacts are far from over.

Thunderstorm chances through the weekend will be primarily limited
to the higher terrain locations of the eastern forecast area. With
predominant sinking motion Friday and Saturday, even these more
favored areas may struggle to see rainfall with only isolated
coverage. Eventually next week, the cycle will resume with more
concentrated storms forming over terrain features and outflow
boundaries descending into lower elevations. Chances for more
comprehensive storms next week may hinge on a couple features: 1)
the expanse of the high pressure ridge and ability to suppress
convection (or lack there of), and 2) the potential for a backdoor
front and PV fracture to shear westward from the trough digging
downstream. The range of ensembles is rather wide advertising
anything from stronger high pressure, heat issues, and deflection of
easterly waves well into northern Mexico to robust easterly wave
activity and resumption of storms and locally heavy rainfall.

&&

.AVIATION...Updated at 0002Z

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

Although isolated showers/TS are still seen on radar across the
higher terrain north and east of Phoenix, with even a couple of weak
showers/storms being seen across the lower deserts well south and
east of Phoenix, current thinking is that chances for storms
impacting the terminals remain quite low (less than 10%). CIGS are
expected to remain mainly aoa 10k feet with gradual clearing
continue through evening/overnight. Current light westerly winds are
expected to switch to easterly during the late evening hours. For
tomorrow, clear skies and diurnal winds are anticipated.

Southeast California/Southwest Arizona including KIPL and KBLH:
There are no major aviation weather concerns with just a few high
clouds and light diurnal wind tendencies.

&&

.FIRE WEATHER...
Saturday through Wednesday:
Rain chances will be very low for all but the far eastern  mountains
of Arizona Saturday, with the rain chances increasing a bit into
early next week and spreading west. Humidity trends will be a very
slow increase while temperatures remain persistently near normal.
Winds will generally follow diurnal trends aside from stronger gusts
in thunderstorm outflows.

&&

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

&&

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

&&

$$

DISCUSSION...18
AVIATION...Percha/AD
FIRE WEATHER...Iniguez