Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 05/19/21

Area Forecast Discussion

National Weather Service Phoenix AZ

 445 PM MST Tue May 18 2021

.UPDATE...Aviation Discussion.

&&

.SYNOPSIS...
A departing low pressure system will bring a slight chance of
showers and isolated thunderstorms over central and eastern Arizona
today. These showers will result in minimal rainfall, with gusty
winds being a more likely impact for the high country and possibly
parts of Phoenix. Temperatures will rebound to near normal today and
then above the seasonal average tomorrow. However, another weather
system will arrive Thursday into Friday, resulting in breezy
conditions and cooler weather.

&&

.SYNOPSIS...
The upper air analysis now shows northerly cyclonic flow aloft at H5
across AZ and the region on the west flank of a closed low pressure
system over N NM. METSAT imagery shows the large cloud shield
cyclonic circulation northeast of the region along with convective CU
developing across the Mogollon Rim. WV imagery depicts elevated
moisture and vort max disturbances rotating around the periphery of
the low.

Current radar reveals very light returns associated with some
sprinkle showers and possibly virga although in a semi-organized
pattern. Current ACARs soundings show PW recently increasing to
upwards of 0.77` and slightly elevated moisture in the upper-mid
levels near 600 mb with low-end CAPE of 310-421 j/kg, with DCAPE
near 875 j/kg.

HREF family members agree on fairly isolated convection for S.
Gila Cty & Mogollon rim as the next PVA disturbance rotates and
pivots through the region. The outlier is the HRW FV3 which is a
little more bullish on the prospects for convection/showers with
a bit better coverage.

The rotating vort lobe(s) will produce sufficient vertical lift and
dynamics to provide a slight to fair chance of scattered to isolated
showers and a thunderstorm over the high terrain areas, with only a
slight chance for NE-E Maricopa Cty and the N-NE-E Phoenix valley
this afternoon and early evening. Although there is a slightly
better chance for a few storm outflows to push into the Phoenix
Valley his afternoon or evening from the north and east with a
gust potential of about 25-35 mph (15-30% chance). This would be
the main impacts of these storms along with an outside chance of
lightning. Any storms are not expected to produce any significant
QPF due to insufficient forecast moisture/PW in the column.

As the low pressure system exits into the southern plains
Wednesday, shortwave ridging will temporarily build back into the
SW Conus allowing temperatures to warm back above the seasonal
normal. By Wednesday, NBM temperature probabilities show about a
75% chance of reaching 100 F or higher. Beyond, Wednesday, another
weather system will impact the region. Ensemble guidance is now
in good agreement that a closed low will develop over the Great
Basin.

WPC clusters show that there is relatively minimal
variation in the big picture through day 5, with the main
uncertainty relating to how far to the southwest the negative
height anomalies will extend. These differences will affect the
magnitude of the breezy conditions that develop as well as the
degree of cooling. In either case, the Wednesday through Friday
period will likely be the windiest. Temperatures will be likely be
the coolest Saturday and Sunday. Rain remains very unlikely.
Ridging and rapidly warming temperatures are likely to return
thereafter.

&&

.AVIATION...Updated at 2345Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The potential for thunderstorms/showers and any related aviation
impacts continues to dwindle as convection has failed to maintain
south of the Mogollon Rim. There is a 10% chance or less for
storms or sudden wind shifts from outflow winds this evening. If
these do occur, the best timing is from now through 03Z and would
most likely cause an early easterly wind shift for KDVT, KSDL
and/or KIWA. Otherwise, westerly winds gusting up to 20-25 kts are
anticipated to last through sunset. The overnight easterly winds
should begin around 10Z tonight and last until late Wednesday
morning/early afternoon when the westerly winds will resume with
gusts once again reaching 20-25 kts. There may be periodic moments
of LLWS for the TAF sites late tonight but confidence in this
reaching TAF thresholds is too low at this time.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will become the primary aviation weather concern by tomorrow
afternoon. Until then, westerly winds will continue at KIPL while
southerly winds continue at KBLH. Both terminals could see some
afternoon and late evening gusts of 20-25 kts. For tomorrow, the
westerly winds will strengthen at KIPL after a brief period of
morning easterly/variable winds. Gusts are anticipated to reach 25
kts and occasionally 30-35 kts. At KBLH, the southerly winds will
become south-southwesterly by Wednesday afternoon with speeds
reaching 20-25 kts and gusting to 30-38 kts. Areas of blowing dust
could reduce surface visibilities while lofted dust could create
slantwise visibility issues.

&&

.FIRE WEATHER...
Friday through Tuesday:
A strong weather disturbance will approach the region during the
latter half of the week pulling temperatures back below normal and
leading to breezy winds. The breeziest conditions will likely
occur Friday afternoon with gusts near 20-28 mph over ridge tops
and exposed areas. With very dry fuels, an elevated fire danger is
possible Friday afternoon, with some threat of critical thresholds
being met locally. Min RH levels will stay near 5-10% through the
period. Overnight recovery will be poor to fair in a 25-50% range
initially, decreasing to 15-35% over the weekend.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Wind Advisory from 3 PM to 11 PM PDT Wednesday for CAZ560-562-
     563-566.

&&

$$

DISCUSSION...Sawtelle/Hodges
AVIATION...AD
FIRE WEATHER...Sawtelle/Hodges