822
FXUS65 KPSR 150825
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
125 AM MST Thu Aug 15 2024

.SYNOPSIS...
Rather quiescent weather conditions will prevail through the
beginning of next week with thunderstorm activity starting to return
to the region over the weekend, albeit mainly confined to higher
terrain areas of Arizona. Temperatures will remain in a slightly
above normal range with afternoon highs reaching near 110 degrees
over the warmest lower desert communities.

&&

.DISCUSSION...
With pronounced negative height anomalies sunken across the Pacific
NW, objective analysis indicates a strong zonal jet continuing to
progress through central California and the Great Basin acting to
dampen subtropical ridging over the SW Conus. South of this jet core,
an impressive midtropospheric subsidence inversion has expanded with
a large pool of H5 temperatures -3C or warmer covering the entire
Southwest. With westerly flow also scouring moisture from the top of
the boundary layer, convective inhibition will be quite overwhelming
precluding much, if any deep convection through Friday across the
CWA. Despite the thermal anomalies aloft, H5 heights are not
particularly unusual (~595dm) resulting in a continuation of
slightly above normal temperatures and widespread moderate
HeatRisk the remainder of the week.

By Friday night, the center of the H5 anti-cyclone will have shifted
across the forecast area into the southern high plains undergoing a
strengthening and amplification phase. This transition will be in
response to an entire Conus pattern amplification with deep negative
height anomalies becoming re-established along the Pacific NW coast
as well as the Great Lakes. This pattern re-alignment will place the
region back into a more traditional monsoon south/southeast flow
capable of importing better quality moisture northward. However,
despite models suggesting low level mixing ratios rebounding into a
more supportive 10-12 g/kg range over the weekend, a measure drier
air residing at the top of the boundary layer and strengthening of
the subtropical high may relegate thunderstorm activity to
mountainous regions of Arizona. Should better deep moisture advect
north from larger Sonoran storm complexes and multiple outflow
boundaries collide over lower elevation population centers, rainfall
prospects could be somewhat better than the paltry 10-15% POPs
advertised by the official NBM forecast.

Through the first half of next week, the upper level flow pattern
will not change tremendously other than the expansion and further
strengthening of subtropical high pressure over New Mexico. Ensemble
mean H5 heights rise closer to a 595-597dm range though some
individual members suggest the center of the anti-cyclone closer to
eastern Arizona with heights peaking closer to 597-599dm. Should
these latter solutions come to fruition, temperatures would
naturally be warmer than forecast with the 75th percentile of the
model spread indicating readings potentially flirting with excessive
heat criteria towards the middle of next week. As the high pressure
system expands, subsidence over much of Arizona should increase with
better moisture and forcing mechanisms displaced into northern
Mexico. This pattern would still support higher terrain storms and
conceivably some activity into lower desert locations, albeit not
widespread by any stretch, though mandated NBM POPs seem a bit low
given the prevailing synoptic pattern.

&&

.AVIATION...Updated at 0500Z.

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 high
clouds, skies will be mostly clear through Thursday evening.


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. Other
than a FEW high clouds filtering in Thursday afternoon, skies will
be mostly clear.

&&

.FIRE WEATHER...
Slightly above normal temperatures will prevail through the
beginning of next week as conditions remain drier than normal by mid
monsoon standards. Higher terrain areas of eastern districts will
stand the best chance for thunderstorms over the weekend, however
wetting rainfall should be very isolated. With drier air already in
place, minimum afternoon humidity levels will fall to around 10-15%
in western districts and between 15-25% for the Arizona districts.
Overnight recovery should be fair to good between 30-60%. Wind
patterns should follow a more typical upslope/drainage pattern
without much chance of gusty outflows the next few days. However,
local afternoon upslope gusts of 20-25 mph will be common.

&&

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

&&

$$

DISCUSSION...18
AVIATION...RW
FIRE WEATHER...18