Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/12/20

Area Forecast Discussion

National Weather Service Phoenix AZ

 520 PM MST Sat Apr 11 2020

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
Scattered showers and a few thunderstorms will decrease in
coverage late this afternoon and end tonight as our lingering low
pressure system pushes into far southeast Arizona. After a brief
break tonight into Sunday morning, another disturbance will bring
additional rain chances to northern and eastern Arizona on Sunday
and Monday, with a slight chance of showers in the Phoenix metro
on Monday. Southeast California and southwest Arizona will remain
dry on Sunday and Monday, with south central Arizona beginning to
dry out on Tuesday with highs climbing above normal by Thursday.

&&

.DISCUSSION...
Isolated to scattered showers and even a couple thunderstorms are
ongoing across south central Arizona this afternoon as the cutoff
mid-to-upper level low along the Mexico-Pima County border is
finally ejecting to the southeast. Showers are also occurring over
higher terrain locations in La Paz and Yuma Counties, but dry air
is rapidly moving in from the west to prevent showers at lower
elevations. This drying trend will continue to sweep eastward
over the next couple of hours to end convective chances over the
Phoenix metro by late afternoon, with aircraft soundings into KPHX
beginning to show this drying trend as well that is keeping our
instability in check despite favorable low-level and mid-level
lapse rates. As previously expected, the best chances for deeper
thunderstorm activity across the Phoenix metro has passed with
only showers expected over the next couple of hours aside from the
far southeast portion of the metro where one thunderstorm south
of Florence is dissipating. SPC Mesoanalysis is also showing that
we have lost our instability, so we continue to have very little
confidence in any convection pushing off the Rim into the Valley
late this afternoon and early evening. Any convection that does
cross into far northern Maricopa County should dissipate quickly
as it moves into lower elevations early this evening.

The aforementioned low will continue to push southeast into Mexico
this evening to set up dry northwest flow across the region
overnight into tomorrow. Global and hi-res model ensembles
continue to show a broad shortwave trough at midlevels moving into
northern Arizona by late Sunday afternoon, triggering another
round of showers and isolated thunderstorms just north of the
region along a weak dissipating front. However, enhanced upper-
level divergence interacting with remnant moisture aloft late in
the overnight hours into the day on Monday should be enough to
help trigger shower activity further south into at least the
Phoenix metro. A few isolated thunderstorms will also be possible
on Monday afternoon, with the best chances over higher terrain
areas north and east of Phoenix as model soundings suggest there
will be much less instability than there was with today`s storm
system. Temperatures over the lower deserts will also continue to
remain several degrees below normal on Sunday and Monday with
highs in the upper 70s and lows in the mid 50s.

A significant warming and drying trend will begin on Tuesday or
Wednesday and continue through at least Thursday as northwest
flow and then more zonal flow aloft persists over the region
behind the departing trough. Temperatures should finally warm back
up to near seasonal normals on Wednesday and above normal on
Thursday as highs climb up into the mid to upper 80s. Forecast
uncertainty is relatively high beyond Thursday as the global model
ensembles are split between zonal flow continuing or another
cutoff low splitting off of yet another shortwave dropping down
from Alberta. For now, we have stuck with temperatures dropping a
few degrees for Friday into the weekend back to seasonal normals
with dry conditions, though a plurality (but not a majority) of
ECM and GEFS members favor troughing suggesting temperatures will
be below normal with some potential for rainfall.

&&

.AVIATION...Updated at 0020Z.

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

Shower activity across the metro this afternoon will continue to
taper off as we head into the early evening hours. Can`t rule out an
isolated vicinity shower near the terminals this evening, but most
shower activity is now diminishing. Winds at this hour have been
variable as a result of various boundaries and showers across
Phoenix. Winds are expected to become westerly/southwesterly again
at the terminals early this evening, lasting into the late evening.
Winds transition to the east later tonight with speeds remaining
below 8 kts. Winds pick up out of the west by early tomorrow
afternoon with some gusts into the teens possible. Otherwise, SCT-
BKN clouds around 6 to 8 kft should scatter out some this evening
with FEW-SCT low to mid level decks remaining throughout the TAF
period.

Southeast California/Southwest Arizona including KIPL and KBLH:

Satellite imagery this afternoon showed mostly clear skies across
southeast California with only some cumulus remaining. Expect clear
to mostly clear skies to continue through the next 24 hours at the
terminals. Winds will favor the west at KIPL while winds favor the
south at KBLH. Winds become breezy by tomorrow afternoon with some
gusts into the low 20s possible.

&&

.FIRE WEATHER...
Monday through Friday:
A weak upper level disturbance moving across the northern half of
Arizona on Monday will bring scattered showers mainly across the
Arizona high country before a drying trend takes place during the
middle part of next week. Below normal temperatures early in the
period will warm to around normal by Thursday. Min RH values
between 25-30% are expected Monday, lowering beginning Tuesday to
below 15% each day. Winds will generally remain fairly light
through the period, but with daytime breeziness likely on most
days.

&&

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

&&

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

$$

DISCUSSION...Hopper/Kuhlman
AVIATION...Smith
FIRE WEATHER...Kuhlman