553
FXUS65 KPSR 142305
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
405 PM MST Wed Aug 14 2024

.Update...00Z Aviation Discussion

&&

.SYNOPSIS...
Quieter weather conditions will prevail during the latter half of
the work week, with relatively stable daily high temperatures
reaching up to around 110 degrees for the typically warmer lower
desert communities through this weekend. High pressure will begin to
shift back over the southern plains this weekend resulting in a
slight increase in moisture and increased thunderstorm initiation
chances mainly over Arizona high terrain into early next week.

&&

.DISCUSSION...
Current WV imagery and 500 mb RAP analysis depicts a trough moving
eastward over the Intermountain West, with another upstream
approaching the Pacific Northwest coast. The persistent Pacific
Northwest negative height anomalies coupled with a strong westerly
jet streak over the Great Basin region has acted to displace/dampen
the subtropical high pressure over the region. An anticylonic
circulation is in place overhead, with very dry air and subsidence
aloft. The 12Z KPSR sounding this morning depicted a strong
inversion between ~600-500 mb associated with the subsidence aloft,
and model soundings show this feature persisting to some extent
through the next several days, becoming less prominent later in the
day on Friday. Considering the strong cap and drier air in place,
shower/thunderstorm chances through the end of the work week will be
near zero, but Friday may bring some very isolated development over
the typical prominent terrain features of Southwestern Maricopa
County, Northeastern La Paz County, and Gila County.

Late Friday, the upper level pattern shifts such that upstream
troughing amplifies just off the West Coast and the subtropical high
builds as it centers itself over the southern plains/eastern New
Mexico. This shift in the pattern will allow south/southeast flow to
reestablish over Southern AZ, drawing moisture back into the region
for this weekend. Global ensembles are in excellent agreement with
respect to the trends in moisture through this weekend, suggesting
PWATs (and lower desert storm chances) will peak late Saturday,
though the GEFS shows the driest ensemble mean compared to the ECMWF
and CMC ensembles. Despite the increase in moisture this weekend,
forecast near-surface mixing ratios (peaking around 10-11 g/kg)
will only be marginally supportive of lower desert storms, and
much of the daily thunderstorm activity will be confined to the
Arizona high terrain and some of the typical mountains/terrain
features of South-Central and Southwestern AZ. NBM PoPs peak
around 10-20% for the AZ lower deserts on Saturday and Sunday and
around 20-40% for the high terrain east/north of Phoenix and for
Southeast AZ. Early next week, the upper level flow pattern does
not seem to change significantly, though the trough off the west
coast and subtropical high both seem to shift slightly westward,
and ensemble mean H5 heights modestly increase over the eastern
CWA to around 595-597 dam. With increased subsidence aloft,
convection would be even more confined to the AZ high terrain
early next week, and lower desert PoPs decrease to 10% or less
starting Monday.

Temperatures will be quite stable through the next 7 days, with
daily highs reaching around 108-112 deg F each afternoon across the
typically hotter lower desert locales. These temperatures will lead
to widespread Moderate HeatRisk through at least the middle of next
week, so sensitive groups will be at risk of heat-related illness
during the heat of the day, and all should continue to practice
proper heat safety measures. As current global guidance indicates
heights aloft increasing over the eastern CWA next week, areas of
Major HeatRisk develop over the San Carlos area as early as
Monday, however, subtle differences in the locations and
orientations of the previously discussed synoptic features could
lead to considerable changes in moisture, magnitude of heights
aloft, and the subsequent temperature forecast, so excessive heat
products are not necessary at this time.

&&

.AVIATION...Updated at 2305Z.

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

No aviation concerns are expected during the TAF period. Winds
will follow typical diurnal trends, with occasional gusts 15-20
kts during the afternoon and early evening hours. Other than a FEW
clouds around 10k ft, skies will be mostly clear through tomorrow
afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns are anticipated through the next 24
hours. Winds will follow familiar diurnal trends, with some
periods of variability during directional shifts, especially at
BLH. Mostly clear skies will prevail during the next 24 hours.

&&

.FIRE WEATHER...
Drier conditions and slightly above normal temperatures will
prevail through the end of the work week, with only isolated (10%
or less) chances for showers and thunderstorms returning late
Friday. Over the weekend, a modest increase in moisture will lead
to better storm chances and coverage. Today and Thursday, with
drier air in place, afternoon MinRHs will bottom out around 10%
for the western districts and between 15-20% for the Arizona
districts. By Friday, these values will increase across the
region to between 15-25%. Overnight recoveries will be fair at
between 25-50% and increase up to 60% for portions of southern
Arizona over the weekend. Wind patterns should follow a more typical
upslope/drainage pattern through the next several days without
much chance of gusty outflows. However, local afternoon upslope
gusts of 20-25 mph will be common.

&&

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

$$

DISCUSSION...Whittock
AVIATION...RW
FIRE WEATHER...Whittock