943
FXUS65 KPSR 110010
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
510 PM MST Sat Aug 10 2024

.UPDATE...Updated 00z Aviation Discussion.

&&

.SYNOPSIS...
Daily shower and thunderstorm chances will continue
through early next week, favoring the higher terrain areas of
northern, eastern, and southeastern AZ, with the best chances for
activity across the lower deserts this afternoon. By the middle
of next week, drier air will filter into the region resulting in a
significant downtrend in thunderstorm activity across the entire
region. The hottest temperatures during the next week will be
this afternoon as highs across most of the lower desert
communities approach 110 degrees. Starting on Sunday and
continuing though the first half of next week, temperatures will
cool down slightly with readings closer to normal levels.

&&

.DISCUSSION...
Convective onset has been much earlier today than yesterday.
Additionally, instability is higher and the cap is weaker.
Noontime mesoanalysis has MLCAPE values between 500-1000 J/kg with
MLCIN greater than -50 J/kg across most of southern AZ and
southeastern CA. Highest instability is being analyzed in western
Pima and southern Maricopa counties, where a weak upper level
vorticity wave is also swinging through. Robust thunderstorms
developed quickly in this area shortly after afternoon, realizing
the instability. The other area to see early storm development was
near the Kofas in La Paz County. Latest HREF keeps the best
coverage of this afternoon`s thunderstorm activity generally
between the Colorado River and just west and southwest of Phoenix,
with isolated activity elsewhere. There is still uncertainty in
the chances for the Phoenix area this afternoon. Recent hi-res
model runs keep thunderstorm activity just outside of the Phoenix
area. However, a strong outflow and colliding outflows will remain
capable of generating storms in the Valley. DCAPE values are in
the 1000-1500 J/kg range, so strong to locally severe downburst
winds will be possible with any storm this afternoon and evening.
The strong downburst winds will be capable of generating localized
dense blowing dust. Moisture levels are also high enough, with
mixing ratios near 11 g/kg, to support heavy rainfall that could
lead to localized flash flooding concerns with any storms that
anchor to a location or if multiple storms hit the same area.

While most of the thunderstorm activity should dissipate after
sundown, there is support for some overnight and morning elevated
convection development in parts of south-central and southwest AZ.
The best chances for elevated convection may coincide with a low
and mid level moisture push from northern Mexico after midnight.
Overnight and morning activity typically is not too strong, but
still capable of producing wetting rains, lightning, and some
gusty winds. The synoptic setup will remain nearly the same
tomorrow through Monday with a low circulation over the Baja
Peninsula and light southeasterly flow into the southern deserts.
Following the moisture push tomorrow morning and with this
synoptic setup, there will continue to be chances for lower desert
thunderstorms and one of the two days may be an active one for the
Valley. It is difficult to say which day is more favorable to see
storms in the Phoenix metro area. Latest NBM PoPs would suggest
tomorrow, with 20-30% chances, while global models support a
vorticity wave from the south moving through south-central AZ
Monday afternoon and evening. Regardless, both days will see
MLCAPE values up to 1000-1500 J/kg and mixing ratios closer to 12
g/kg. This will support potential for strong storms, that could
briefly become severe, and storms capable of producing heavy
rainfall with the potential for localized flash flooding. Blowing
dust will remain a risk as well with any thunderstorm outflows.

.PREVIOUS DISCUSSION...
Heading towards the middle to latter of the week, a significant
pattern change is expected to occur across the western CONUS as a
polar trough is expected to move from the Pacific Northwest through
the Intermountain West Region. This will result in southwesterly
flow across the region, which will significantly scour out the
monsoonal moisture with the latest GEFS and EPS indicating mean
PWATs between the Wednesday through Friday time frame decreasing
to between 1-1.2" across south-central AZ the lower deserts to
less than one inch across the western deserts. Therefore, storm
activity is expected to be mostly absent and this is reflected in
the latest NBM guidance which shows PoPs across the lower deserts
at less than 10% with slight chances remaining across the higher
terrain areas of eastern AZ. Heading into next weekend, the
ensembles indicate that as the aforementioned polar trough moves
into the eastern half of CONUS and the subtropical high rebuilds
near Four corners region, a return to easterly flow and thus
increasing monsoonal moisture is likely, with storm chances
returning.

High temperatures today are expected to be the hottest of the next 7
days as highs across most of the lower desert communities
approach 110 degrees. Then, starting on Sunday and continuing
through early next week, temperatures are expected to slightly
cool off with readings returning back closer to normal.
Temperatures during the second half of the week may trend slightly
warmer but still remain below 110 degrees across the majority of
the region.

&&

.AVIATION...Updated at 0010Z.

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

VCSH/VCTS conditions have developed at KIWA, with VCTS conditions
developing going through the evening hours across all TAF sites.
Outflow winds have shifted winds southwestward at KPHX, but a
southerly to southeasterly outflow is expected to shift the winds
shortly after 00z. Best TS chances at KIWA at this time until
around 01z. VCTS conditions possible across the metro from 00-03z.
Lower confidence in wind trends should TS conditions develop
across portions of the metro, but generally brief periods of
southeasterly winds with initial outflows should turn back
southerly to southwesterly into the overnight hours. Winds will
then resume typical diurnal tendencies through tomorrow morning
and into the afternoon hours. Sky conditions will remain SCT-BKN
through the evening to overnight hours before becoming FEW-SCT by
tomorrow morning. Cloud bases should remain aoa 9 kft, except for
any TS development, where cloud bases could dip to around 6-8 kft.

Southeast California/Southwest Arizona including KIPL and KBLH:

VCTS/TS conditions at KBLH over the next several hours will be the
most noteworthy aviation impacts through the forecast period. An
outflow boundary emanating from convection moving westward across
Yuma and La Paz Counties will reach both terminals this evening.
For KIPL, winds should remain southeasterly, with some gustiness
with 20-25 kts with the outflow passage. Can`t rule out some
haziness or reduced visibilities due to lofted dust as the outflow
winds move through KIPL, but there are no VCSH/VCTS expected to
develop. For KBLH, VCTS conditions, with TS conditions possible,
over the next several hours are possible as thunderstorms
approach from the east. Initially, blowing dust reducing
visibilities may become an issue, followed by TS developing in the
vicinity or at the airfield, causing further reductions to
visibility between 00-02z. Winds could also gust 30-40 kts from
the east to southeast direction during this period, as seen in the
TEMPO group. After TS conditions subside, winds should remain out
of the southeasterly direction, before veering back to the
southerly direction through the overnight hours. Gusty winds are
expected to develop during the late morning hours tomorrow at
KBLH, gusting 20-30 kts going through the afternoon hours.

&&

.FIRE WEATHER...
Shower and thunderstorm chances will persist into early next week,
mainly favoring the higher terrain areas of AZ, with the best
chances and coverage across the lower desert areas this afternoon
and early evening. Any thunderstorm will remain capable of
producing locally wetting rains and strong winds, with potential
for outflow winds to travel long distances and cause sudden wind
shifts. Storm activity is expected to trend downward significantly
by the middle to latter half of next week as drier air filters
into the region. Outside of the thunderstorm activity, the general
winds will continue to exhibit the typical diurnal tendencies
with the typical afternoon upslope breeziness. MinRHs will remain
somewhat elevated through early next week with values of between
20-30%, before trending lower into the 15-25% range heading
towards the middle of next week. The hottest temperatures over the
next 7 days are expected today as highs across most of the lower
desert communities approach 110 degrees. Slightly cooler temperatures
are expected starting on Sunday and will persist through the first
half of next week as readings trend closer to normal.

&&

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

$$

DISCUSSION...Benedict
PREVIOUS DISCUSSION...Lojero
AVIATION...Young
FIRE WEATHER...Lojero/Benedict