053
FXUS65 KPSR 230540 AAA
AFDPSR

Area Forecast Discussion...Updated
National Weather Service Phoenix AZ
1040 PM MST Mon Jul 22 2019

.UPDATE...Updated aviation discussion.

&&

.SYNOPSIS...
Thunderstorm chances will increase today and Tuesday across
south-central and southwest Arizona as more substantial moisture
has moved into the region. Areas of blowing dust are also
possible. High pressure will slowly build west towards central
Arizona and result in a slight warming trend into the late week,
with slight chances for thunderstorms will continuing.

&&

.DISCUSSION...
The air feels as if the monsoon has officially arrived with
surface dew points in excess of 60 degrees across all of the
forecast area. Visible satellite this morning revealed thick
cloud debris from a decaying MCS over southern Arizona and Sonora
with a few very light embedded showers across western Arizona.
The cloud cover has been clearing somewhat through the the early
afternoon, mostly to the northeast over the Rim and southern
Arizona. Models continue to highlight afternoon convection
initiating over the White Mountains and southeast Arizona where
instability is greatest with the clearing. Confidence is
moderately strong that those storms will send outflows capable of
generating blowing dust in the lower desert impacting much of
Maricopa and Pinal Counties. Additional convection may also push
the dust threat into western Arizona and southeast California
tonight. A Blowing Dust advisory has been issued for Maricopa and
Pinal Counties to highlight the greatest anticipated dust threat
for those areas late this afternoon and evening.

Confidence is highest for thunderstorms across the higher terrain
north and east of Phoenix and across southern Arizona, assuming
the clearing persists, where 15-20 kts of midlevel winds may
support organized storms capable of producing very strong winds.
An inverted V sounding profile also supports the threat of strong
gusts from thunderstorms. The lower desert, including Phoenix,
will likely have to wait for outflow interactions to initiate
convection late this evening as CAMs suggest storm coverage will
be more isolated. Remaining cloud cover over the lower desert is
reducing instability and confidence for storms in the Phoenix area.
There is also a concern that mostly southerly anvil level winds
may cloud over portions of the Valley further reducing
instability. This scenario is supported by several regional and
global models, as well as the GEFS plumes. This trend is also
reflected in many of the HREF members painting the northern,
southern, and western portions of Maricopa County as more likely
to see storm development as compared to the central Valley
(depending on outflow interaction). Still, the greatest concern
for today will be a blowing dust hazard.

Convection may also spread into the western portion of the forecast
area this afternoon and tonight. Storms formed early this
afternoon along the mountain ridges in the northern Baja Peninsula
in response to a vort max lifting through the area. Additional
isolated activity may also redevelop late tonight closer to the
Colorado River.

Later in the week, the position of the mid-level anticyclone will
meander slowly southwestward across the Four Corners and
eventually near central Arizona by this weekend. This will result
in a slight warm up, with temperatures near or just above 110
degrees Friday and Saturday, but excessive heat should be held in
check. A slight downtick in convective activity across the lower
deserts may also occur Friday and Saturday amidst a drier air mass
and warmer temperatures aloft. By this weekend, mid-level high
pressure will gradually re- build northward and should allow
enough moisture to return for continued slight chances of
thunderstorms each day from Sunday into early next week.

&&

.AVIATION...Updated at 0540 UTC

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

Impressive convective complex developed across east and southeast
Arizona during the afternoon and evening, but for the most part
thunderstorms have dissipated. Expect some continued showers past
midnight in the Phoenix area so will mention VCSH in the TAFs but
after about 08z, opted to drop the showers. Cannot rule them out
through the overnight hours given thick mid/high level debris clouds
remaining but coverage will be rather sparse if the showers do
linger. Strong gusty southeast outflow winds will continue to
diminish and will do so over the next few hours with lighter east
wind then persisting through the morning on Tuesday.

One small note...another outflow boundary was moving south and into
the far northern portion of the Phoenix area...fighting through the
strong southeast outbound winds...and we will likely see winds shift
to the north at KDVT for a couple hours. Do not expect those north
winds to impact KPHX or KSDL and as such they are not mentioned in
the TAFs, but cannot rule out another wind shift from the north over
the next hour or so. Otherwise expect lots of lingering mid/high
clouds tonight into Tuesday with most bases aoa 10k feet.

Convective potential remains high for Tuesday, so we may see another
round of storms and outflow winds Tuesday late afternoon and
evening. Opted to mention another wind shift to the east/southeast
after 03z Tuesday evening...but confidence too low attm to mention
thunder, dust or vis restrictions.

Southeast California/Southwest Arizona including KIPL and KBLH:

For the next 24 hours, convection should not be much of an issue for
the western deserts, we are mainly looking at lots of mid/high
clouds with BKN-OVC cigs mostly 15k and up. An isolate shower might
be possible overnight tonight but confidence too low to mention in
the TAFs. Winds will favor the southeast most of the TAF period at
KIPL with an outside chance for winds to turn to the southwest for a
few hours this evening. Winds to favor the south at KBLH next 24
hours although there is potential for a few hours of gusty east wind
to move in - most likely after 09z - due to convection spreading
westward across the southwest Arizona deserts tonight. Feel speeds
would likely stay under 25kt if those outflow winds actually
materialize. Confidence in them is rather low attm.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Thursday through Monday:
Temperatures will undergo a slight warming trend through the
weekend. Lingering moisture will keep minimum RH values near 15%
with overnight recoveries into the 30-40% range. Rain chances will
dwindle and primarily be confided to the higher terrain north and
east of Phoenix. Outside of any thunderstorms, the Winds will
favor diurnal directional tendencies with occasional afternoon
breezes.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Severe Thunderstorm Watch until 11 pm this evening for
     Maricopa County - AZC013.

CA...None.
&&

$$

DISCUSSION...Deems/Rogers
AVIATION...CB
FIRE WEATHER...Deems

NWS PSR Office Area Forecast Discussion