544
FXUS65 KPSR 132121
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
221 PM MST Tue Aug 13 2024

.SYNOPSIS...
Temperatures will remain fairly steady over the next several days
with highs around 3-5 degrees above average across the lower
deserts. Rain chances will decrease substantially through the
remainder of this week as dry, westerly flow sets up over the
region. The subtropical high will then begin to shift over the
Southern Plains this weekend resulting in a slight uptick in
moisture this weekend, leading to increasing thunderstorm chances
over the AZ high terrain.

&&

.DISCUSSION...
Latest mid-lvl water vapor imagery and 500 mb streamline analysis
reveals a trough of low pressure centered over the Pac NW while
the subtropical high is now displaced east of the region over the
Southern Plains. AZ is located between both of these features with
westerly flow aloft prevailing. Noticeably drier air is beginning
to filter into the western portions of the state, however a
subtle shortwave embedded in the large scale trough has helped
facilitate ongoing convection across southcentral AZ. We have
already seen isolated thunderstorm activity in the Phoenix Metro
area, but much of the activity for the remainder of today should
be confined to the higher terrain of Maricopa and S Gila counties.
As dry air aloft begins to move into the region tonight, storm
coverage will diminish with mostly clear skies expected. Lows will
fall into the low to mid 80s for most desert communities and into
the mid 70s across the foothills.

For the remainder of this week, troughing to our north will keep
the overall ridge of high pressure suppressed with 500 mb hght
anomalies remaining near normal. This will result in highs
remaining at or slightly above normal across the lower deserts,
or largely below 110 degrees. PWAT values will decrease to the
0.8-1.2" range across the region beginning on Wednesday, which is
unfavorable for thunderstorm development. Global ensembles
continue to indicate a reinforcing Pacific trough digging across
the Intermountain West on Thursday and Friday, which will delay
the subtropical ridge from building back into our region. NBM PoPs
remain around 5% or less across the entire CWA for Wednesday-Friday.

Heading into this weekend, a deeper trough will dig off the coast
of the Pac NW, allowing the subtropical ridge to strengthen over
NM/TX. This pattern shift will result in a return of southerly to
southeasterly steering flow over southcentral AZ and provide a
slight uptick in moisture. In response, daily storm chances will
return beginning on Saturday. PoPs will mainly be confined to the
higher elevations of AZ with only around 10-20% chance of storms
surviving into the lower deserts. Temperatures will not fluctuate
much through the weekend. Afternoon highs will reach 105-110
degrees across the lower deserts and in the 90-100 degree range in
the higher terrain areas. Thus, HeatRisk will continue to be
Minor to Moderate with no excessive heat on the horizon.

&&

.AVIATION...Updated at 1830Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Only minimal weather impacts are possible through Wednesday under
periods of FEW-SCT mid/high cloud decks. Winds will establish out
of the W over the next hour or so, with some gusty, erratic
behavior possible with the TS over the Central Valley as it moves
off to the northeast. The only terminal expected to have direct
TSRA impacts will be KSDL through 20Z. Some isolated shower
development (10% chance) will be possible later this afternoon
(after 22Z), but confidence is too low to include at this time.
Otherwise, west winds may hold well later than usual tonight, and
perhaps closer to sunrise Wednesday morning.

Southeast California/Southwest Arizona including KIPL and KBLH:
No weather issues will exist through Wednesday morning under
clear skies. Winds will maintain a southerly component varying
between a daytime SE and evening SW component. Gusts may be more
prevalent today with 20-25kt possible at both terminals.

&&

.FIRE WEATHER...
Scattered showers and thunderstorms will be possible this afternoon
and evening across eastern Maricopa and southern Gila Counties. The
main threats include localized flooding, frequent lightning, and
gusty erratic winds. Drier air will filter into the region through
the later half of the week with little to no thunderstorm activity
expected. Aside from convectively induced outflow, winds will follow
their typical diurnal patterns with gusts up to 15-20 mph each
afternoon. MinRH values will range from 15-25% range across the
central AZ districts and in the 10-20% range across the CA districts
through Friday. Overnight recovery will peak around 25-50% over the
next few nights. Temperatures will remain largely unchanged through
this weekend with highs running slightly above normal.

&&

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

$$

DISCUSSION...Salerno
AVIATION...Whittock/18
FIRE WEATHER...Salerno