206
FXUS65 KPSR 021738
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1038 AM MST Fri Aug 2 2024

.Update...
18Z Aviation Discussion.

&&

.SYNOPSIS...
A traditional monsoon thunderstorm setup is expected today through
this weekend with daily afternoon storms primarily favoring the
high terrain areas of northern and southeastern Arizona and with
low chances of surviving into the lower deserts of south-central
Arizona. Strong high pressure over the region will lead to most
lower desert communities experiencing Major to Extreme heat risk
this weekend through Monday as afternoon high temperatures exceed
110 degrees. A weather disturbance next week may bring more active
monsoon conditions and slightly cooler temperatures.

&&

.DISCUSSION...
Regional radar shortly after midnight shows a mass of showers and
storms moving through NW AZ, associated with mid-level vorticity
embedded within the southeasterly and easterly flow across the
region. Mid-level water vapor imagery also shows evidence of
multiple mid-level gravity waves moving about the region. With
several hundred joules of instability still being analyzed, it is
not out of the question to see an isolated shower or storm here or
there across the southern deserts through the remainder of the
nighttime hours.

Taking shape for this afternoon will be a more traditional
monsoon setup with high pressure strengthening and repositioning
near the Four Corners. Objective analysis is already showing H5
heights near 599-600 dm in this region. Under this more
traditional setup, afternoon storm chances will mostly favor the
high terrain areas of AZ, mainly northern and southeastern AZ, but
also places like the Tabletop Mesa area of Southwest Maricopa
County and across La Paz County. With southeast flow there is
potential for storms and their outflow boundaries to drift toward
the lower deserts of South-Central AZ, but odds of seeing storms
in places like Phoenix are not great (NBM PoP <10%), owing mostly
to limited instability (MLCAPE <1000 J/kg) and a strong capping
inversion. It would take a strong outflow and more likely
colliding outflows for storms to develop in this environment. With
hotter temperatures and a little bit drier PBL conditions, DCAPE
values will be high, up to 1500-1900 J/kg around the region. So,
there will at least be potential for very strong outflows where
storms develop. Through this weekend there will be little change
in the forecast, with similar synoptic and environmental
conditions. Daily thunderstorms are expected in the AZ high
terrain and storms more than likely will struggle to survive into
the lower deserts of South-Central AZ (NBM PoPs remain <10% for
the Phoenix area.

With the strong Four Corners high pressure, leading to H5 heights
up to 596-598 dm over the area, most of the region will see well
above normal temperatures this weekend into Monday next week. An
Excessive Heat Warning is in effect for most lower desert
locations Saturday through Monday. With near record high
temperatures being forecast for some areas, including Phoenix (see
CLIMATE section below), most lower desert communities are
expected to experience Major to Extreme HeatRisk. Lower Desert
highs are forecast to reach the 110-116F range, with little
overnight relief as morning lows will only dip into the upper-80s
to lower 90s. There is even potential for daily record warm lows.
Phoenix record warm lows this time of year are in the low-90s.

Heading through early next week, global models continue to support
an IT rounding the base of the high and progressing into the
Sonoran Desert, at some point in the Monday afternoon to Wednesday
timeframe. With this wave, an increase in moisture is expected,
with most global ensemble members supporting a return of PWATs
into the 1.5-1.8" range. Additionally, the wave may lead to
increased mid-level easterly winds, which combined with the
increased moisture could lead to a more active monsoon
thunderstorm period with greater storm coverage and better storm
organization. At this far out, the forecast is still a little bit
speculative and there are are still some uncertainties in terms of
timing, trajectory, and intensity of the wave. The latest NBM
still has the greatest coverage of PoPs and highest PoPs on
Tuesday next week. Aside from the storms, the wave should help
abate temperatures a little bit from the weekend, but current NBM
forecast only "cools" temperatures a little bit with highs still a
few degrees above normal during the middle to latter half of the
week.

&&

.AVIATION...Updated at 1730Z

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Showers and thunderstorms will remain confined to areas just
outside of the Phoenix Metro area today and tonight. There is a
low chance (10-30%) of an easterly outflow reaching the terminals
this evening, mainly at KIWA. Otherwise, no aviation impacts are
expected with winds continuing to follow typical diurnal trends.
There may be a couple hrs of calm and vrb winds at KPHX before
winds ultimately shift out of the W by 21Z. Winds will return to
the ESE around 05Z-07Z tonight. Skies should generally remain FEW-
SCT through this afternoon, with the lowest bases around 15k ft.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are expected during the TAF period. Winds at
both terminals will follow diurnal tendencies with southerly flow
continuing at KBLH and southeasterly winds favored at IPL through
early this evening before becoming westerly after sunset. FEW to
occasionally BKN mid and high clouds will prevail over the region.

&&

.FIRE WEATHER...
Daily afternoon thunderstorms are expected through the next week.
Today through this weekend storms will primarily favor high
terrain areas of northern and southeastern AZ, as well as a couple
of common spots for isolated activity like the Tabletop Mesa area
of southwest Maricopa AZ and the Kofas to Harquahala Mtns of La
Paz County. Chances will be low (<10%) for storms in the lower
deserts of south-central AZ and in southeast CA. During the early
to middle portions of next week there may be an increase in storm
activity as moisture increases with a disturbance moving in from
the east. Any storm will be capable of strong gusty winds and quickly
producing wetting rains. Otherwise, CWR will be low (10% or less).
Aside from thunderstorm outflows, winds will be fairly light, with
afternoon 15-20 mph gusts, and follow typical diurnal trends.
Minimum RH values will mostly reside in the 10-25% range through
this weekend and increase slightly, mostly above critical levels,
by the middle of next week. Overnight RH recovery will mostly be
around 30-50%, with driest conditions Saturday and Saturday night,
followed by an improvement with the increase in moisture toward
the middle of next week.

&&

.CLIMATE...

Phoenix Daily Record High Temperatures

8/2   113 (2011)
8/3   114 (2020)
8/4   116 (1975)
8/5   116 (2023)

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning from 10 AM Saturday to 8 PM MST Monday
     for AZZ530>555-559-560.

CA...Excessive Heat Warning from 10 AM Saturday to 8 PM PDT Monday
     for CAZ560>570.

&&

$$

DISCUSSION...Benedict
AVIATION...Salerno
FIRE WEATHER...Benedict
CLIMATE...Benedict