Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/15/21

Area Forecast Discussion

National Weather Service Phoenix AZ

 404 PM MST Sat Aug 14 2021

.UPDATE...Updated aviation discussion.

&&

.SYNOPSIS...
High levels of moisture will remain entrenched across the Desert
Southwest through the middle of the week, leading to persistent
chances for showers and thunderstorms. The primary threats with any
storms remain localized heavy rainfall that may cause flash
flooding. A Flash Flood Watch is in effect for south-central Arizona
through Sunday afternoon. Strong winds and some blowing dust will
also be possible for desert locations. With increased cloud cover
and showers, temperatures will remain below normal.

&&

.DISCUSSION...
A very moist airmass remains in place across the region today.
Mesoscale analysis shows regional PW ranging from ~1.4-1.9"+ with
the 12Z PSR sounding showing PW of 1.77" and a late morning PHX
ACARS soundings indicating a comparable mean PW of 1.8". The 12Z
sounding also featured a worked-over, more stable column with a
near moist adiabatic profile,relatively weak CAPE and moderate
CIN. Though significantly higher MUCAPE was developing midday and
back in the 1000s as shown on the RAP and ACARS, although with CAPS
also present. The UL pattern depicted pronounced E flow aloft
along the S flank of the UL ridge with the latest inverted trough
and vort max over S-E AZ with additional disturbances lined up
over S NM/W TX to the east preparing to ride the easterly flow
conveyor belt into the region. METSAT showed mostly cloudy to
patchy clear conditions as radar painted scattered showers and
thundershowers across SE-E AZ and into Pinal County SE of Phoenix.

After last night`s widespread storms dewpoints remained very high
from the upper 60s to mid 70s in the early afternoon along with
enough breaks in the clouds to produce increasing afternoon
insolation and heating around Phoenix and the lower deserts. HREF
members have divided into two camps for this afternoon and
tonight. The ARW and the HRRR favor a smaller area of storms
descending from S Gila Cty into the SE-S-Central Valley while
weakening as they enter the Valley this evening around 8-9PM MST.
In the other camp are the significantly more bullish NSSL, FV3 and
NAM NEST which favor more numerous, robust storms over a larger
area descending off the E high terrain and not weakening as much
as they cross Phoenix. The UL triggering mechanism disturbances in
place support the latter/stronger storm scenario, while the
possible lingering effects of a recently worked-over column
support the former/weaker storm scenario. In either case there
remains a good 40% NBM chance of precipitation tonight and a 50%
chance of HREF thunderstorm wind gusts of >35 mph across Phoenix
and the deserts tonight. There`s also almost a 10% HREF chance of
thunderstorm wind gusts of 60 mph tonight across the lower deserts.

The current upper level pattern changes very little on Sunday and
into the early part of the week. As a result a flash flood watch
remains in effect for the region (not including SW AZ and SE CA)
through Sunday afternoon at 5 PM MST. Temperatures today and for
the week will also change very little and remain below normal, in
the upper 90s to near 100, owing to the persisting highly humid
airmass conditions.

The Clusters family favors similar flavors of a large, weak low
pressure trough anomaly dominating the Intermountain West and N.
Rockies by the middle of the week as well as disturbances and
associated storms lifting out ahead of it across Phoenix and the
AZ area. As a result expect elevated chances of storms and
precipitation through the middle of the week.

&&

.AVIATION...Updated at 2305Z.

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

Still some potential for shower/thunderstorm activity across parts
of the Phoenix metro area this evening, with higher chances for an
outflow moving through. Still some uncertainty as to how
widespread any activity will be given that the air mass is
slightly more stable compared to yesterday. Winds from east to
northeasterly outflow are expected to arrive near or after 02Z,
with gusts of 20-30 kt possible. Otherwise, easterly winds should
persist overnight into much of Sunday morning. Expect SCT-BKN
clouds to persist mostly aoa 6 kft, though cigs could drop down
with any convection that develops over the metro later.

Southeast California/Southwest Arizona including KIPL and KBLH:

At KIPL, light winds should persist out of the east to southeast for
the bulk of the TAF period, while winds are expected to remain
southerly for KBLH. FEW-SCT clouds aoa 12 kft are expected to
persist throughout the period.

&&

.FIRE WEATHER...
Monday through Friday:
Humid conditions will continue through much of the week. The
threat of showers and thunderstorms will also continue through
midweek, followed by a drying trend and only a slight chance of
wetting rains. The strongest storms early in the week will be
capable of producing localized flash flooding, particularly in the
higher terrain north and east of Phoenix. Below normal
temperatures are also anticipated.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flash Flood Watch through Sunday afternoon for AZZ534-537>563.

CA...None.
&&

$$

DISCUSSION...Sawtelle
AVIATION...Rogers/Smith
FIRE WEATHER...Hirsch