Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 03/14/21

Area Forecast Discussion

National Weather Service Phoenix AZ

 504 PM MST Sat Mar 13 2021

.UPDATE...
Updated 00Z aviation discussion.

&&

.SYNOPSIS...
The slow moving low pressure weather system will continue to bring
mostly light shower and isolated thunderstorm chances to the eastern
half of Arizona this afternoon and evening and cool conditions for one
more day. Temperatures will warm to just shy of normal for Sunday
and Monday, but a passing dry weather system late Monday into
Tuesday will lower high temperatures back into the 60s on Tuesday.
This fast moving weather system will also bring a period of
breezy to locally windy conditions on Monday. Warming conditions
through the latter half of next week should push high temperatures
well into the 80s by next Thursday or Friday.

&&

DISCUSSION...
The slow moving UL closed low pressure system was centered just
west of the 4-Corners area with the H5 trough axis and
corresponding cold core migrating through E AZ east of Phoenix
with northwesterly flow aloft. Afternoon WV imagery shows the
associated elevated moisture field, including wrap-around
moisture, passing through the area with a number of vort lobe
clusters/mini PVA disturbances rotating around it. This included
an upstream mesoscale trough axis on the west flank of the main
low northwest of the region.

SPC mesoscale analysis and the latest ACARS soundings confirm a
relatively elevated BL and mid-level moisture profile with a
saturated layer extending from near 760-650 mb and PW values near
0.45". The analysis also indicated weak CAPE/instability. Early
afternoon radar showed a large area of scattered popcorn showers
and an isolated thunderstorm mainly to the E-NE-SE of the Phoenix
Valley. Another modest area of rain and showers associated with
the next mini disturbance was near Lake Pleasant and Black Canyon
City. Visible satellite indicated slightly drier air and a CU
field west of Phoenix.

The HREF CAM family is in good agreement on a temporary lull in
shower activity with some drier air moving in from the west for
mid afternoon, with another small round of showers developing in
NE Maricopa County northeast of Phoenix associated with another
mini-lobe for the late afternoon. Then a final wrap-around lobe
disturbance is likely to trigger the last round of mostly light
and some moderate showers in the Phoenix area during this evening
after sundown. In the last 3 days Sky Harbor has received 0.37" of
rain. Another ~0.02-0.07" of precip for Sky Harbor can not be
completely ruled out for this evening and/or tonight. In
addition, forecast soundings indicate a ground fog signature for
early Sunday morning.

Highs today will be around 16-20 degrees below normal with highs
topping out in the mid to upper 50s to near 60. On Sunday the low
pressure system exits to the east and recovering heights ahead of
a brief high pressure system early Monday will allow temperatures
to rebound into the upper 60s to low 70s on Sunday and low-mid
70s for Monday.

Late Monday into Tuesday ensembles are in good agreement on
ushering in a very progressive compact Pacific closed low pressure
system from the northwest, although there is some uncertainty on
its latitudinal position. The most likely positions range from
N-Central AZ to the 4-corners. A slight ensemble preference for a
slightly more southerly track has resulted in some fleeting
increased POPs for the Phoenix and NE Maricopa cty area for Monday
evening and night. However the main moisture field continues to
favor areas further north. What is more certain is the prospect of
very breezy to windy conditions for SE CA and SW AZ for Monday
afternoon and evening. Areas of blowing dust may also be a concern
for that area. In addition enough CAA is expected to drop highs
back down into the mid 60s for Tuesday.

For the later half of the week the cluster analysis favors the
development of a strong to very strong anomalous ridge of high
pressure over the west-Central CONUS and the Desert Southwest. The
heat signature pattern is likely to result in highs in the low
80s by Thursday, and the mid-upper 80s by Friday.

&&

.AVIATION...Updated at 0004Z.

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

Shower activity through this evening with lowering ceilings and
visibilities along with brief wind gusts will be the main
aviation concern before conditions improve on Sunday. One last
round of isolated to scattered showers and a thunderstorm or two
is expected mainly between 01-04Z as a shortwave rotating on the
southwest edge of the exiting upper level low moves through the
Phoenix terminals. This should cause brief periods of 5 SM or
lower visibilities and ceilings as low as 4 kft within showers,
with more persistent BKN ceilings as low as 6 kft. Convective
coverage will be highest at northern and eastern terminals
including KDVT, KSDL, and KIWA where TEMPO groups are in place
this evening, with lower coverage and thus confidence for KPHX and
West Valley terminals. Wind gusts up to 25 knots will be possible
with these showers, with westerlies becoming east or southeast by
05-06Z once the showers push east of the region.

A brief period of low-level wind shear around sunrise is possible
if E-SE winds increase above 10 knots against westerly 20 knot
just 1-2 kft above the surface. However, confidence is too low to
include this in the TAF at this time. very patchy fog is also
possible by sunrise if winds become calm, but this appears
unlikely at this time. Westerlies should return by early
afternoon with gusts up to 20 knots by late afternoon.


Southeast California/Southwest Arizona including KIPL and KBLH:

Strong westerly wind gusts through early Saturday evening will be
the main aviation weather concern with minimal concerns otherwise
through Sunday afternoon. Strong downsloping westerly winds at
KIPL will gust up to 25-30 knots through 05Z before gradually
subsiding below 15 knots overnight and remaining below 10 knots
for the rest of Sunday. Southwesterly winds at KBLH will subside
below 20 knots by sunset, with winds remaining below 10 knots
until gusting up to 20 knots again on Sunday afternoon. Aside from
very isolated showers briefly lowering ceilings over southwest
Arizona early this evening, only a few passing high cirrus clouds
are expected through the rest of that TAF period.

&&

.FIRE WEATHER...
Monday through Friday:
A mostly dry weather system will track across northern Arizona
late Monday into early Tuesday. This system will bring locally
windy conditions Monday afternoon, especially across southeast
California and southwest Arizona where gusts of 30-40 mph are
likely. Minimum afternoon humidity levels in a 15-25% range are
expected for Monday, lowering to around 10-15% by Wednesday. After
a cool day on Tuesday, temperatures will quickly warm to well
above normal by Friday. Humidity levels late next week will also
remain low with minimum readings in the single digits to around
10%. Overnight recoveries early in the period will mostly reach
40-50%, before dropping to 25-35% late next week.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Wind Advisory until 10 PM PST this evening for CAZ562.

&&

$$

DISCUSSION...Sawtelle
AVIATION...Hopper
FIRE WEATHER...Kuhlman