751
FXUS65 KPSR 150612
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1112 PM MST Sun Jul 14 2024

.UPDATE...Updated 06z Aviation Discussion.

&&

.SYNOPSIS...
Increased thunderstorm activity is expected through this afternoon
and evening, with a slight chance for activity to survive into the
Valley. Strong winds and localized dense blowing dust will be the
primary concerns with these thunderstorms, along with localized
flash flooding. Daily thunderstorm activity will continue through
the early work week, but mostly be confined to the higher terrain
before chances increase again across the lower deserts for the
second half and into next weekend. Temperatures through the week
will remain above normal with lower desert highs in the 110 to 114
degree range.

&&

.DISCUSSION...
A gulf surge last night has created pretty muggy conditions as
morning dew points rose into the middle to upper 60s across
southern AZ to even lower to middle 70s in Yuma to the Imperial
Valley. Some of this lower level moisture will scour out with
daytime mixing through this afternoon, but enough PBL moisture
will remain to support regionally high MLCAPE values (1000-1500
J/kg) this afternoon across the southern deserts. DCAPE values
will also be quite high (up to 2000 J/kg) today as afternoon
mixing steepens the low level lapse rates and the PBL depth
increases up to around 10K ft. Considering these parameters, plus
the overall better moisture, with PWATs up to 1.5-1.7" and mean
mixing ratios around 11-13 g/kg, there is potential for all manner
of monsoon thunderstorm impacts today (i.e. strong-severe wind
gusts, blowing dust, localized flash flooding, and frequent
lightning).

There is potential for high impacts from thunderstorms later today,
given the environment, but it will be a matter of realizing the
instability. For the lower deserts there is a lot of CIN (i.e. a
strong cap) that will have to be overcome. So, it will likely take
strong, deep, outflow boundaries and/or colliding outflow boundaries
from the storms that develop over the terrain features this
afternoon and evening. Given the high DCAPE, this is certainly
possible. For AZ, objective analysis and the latest HREF paint the
greatest arc of instability from eastern Pinal, through Gila, and
into central Yavapai County. Based on the latest HREF, there are
better chances of outflow winds and storms descending from the north
and northeast of Phoenix, with a little less certainty from the
south due to uncertainty in storm coverage in Pinal County. Timing
on activity into the South-Central AZ lower deserts looks to be late-
evening/early tonight, after 6-7 PM MST. In Southwest AZ, the main
area of storm activity will likely be the Kofas region, in northern
Yuma and central La Paz counties. Further west, there is a risk for
high impacts from storms in Southeast CA as well, with potential for
strong storms to drift off the Peninsular Mtns of northern Baja and
SoCal into parts of Imperial County. Greatest risk in Imperial
County will be strong outflow winds that could kick up dust/sand. In
Riverside County, upslope flow could lead to localized flash
flooding concerns in or around Joshua Tree NP. There will be a
localized flash flooding risk elsewhere this afternoon and evening,
as storms will be capable of producing rain rates in excess of 1"/hr.

On Monday, the overall synoptic setup will be similar to today,
with the monsoon high near the Four Corners region, inducing deep
southeasterly flow across the Sonoran Desert. There even looks to
be more of the morning-midday ACCAS convection across Southwest
AZ and Southeast CA. The main difference noted in modeling is a
slight decrease in moisture, a degree or two cooler on the
temperatures, and thus slightly lower instability. So, it is not
out of the question that storms could propagate on outflows into
South-Central AZ, but if the environment is overturned this
evening-tonight, then storms Monday will be even less likely.
After Monday, afternoon and evening thunderstorms are expected to
develop daily as seasonal to above normal moisture lingers in the
region. Most activity will remain confined to higher terrain areas
of AZ, with outflow winds still capable of descending through the
lower deserts. Toward the second half of this week and heading
into next weekend global models indicate a slight increase in
moisture again and a repositioning of the monsoon high back toward
the Vegas area. This setup, a Maddox et al. Type II setup could
lead to a much more active period with a more favorable Rim to
Valley storm trajectory. It will remain to be seen, but the second
half of July through mid to late August is typically when the
monsoon is most active in terms of severe and flood warning
counts.

Besides the storms, the Excessive Heat Warning which was in effect
for over a week came to an end for the AZ deserts yesterday, but
was continued through this evening for Southeast CA mainly due to
heat indices being forecast to reach 114-117F this afternoon.
Beyond today, temperatures will remain hot, just not quite
excessive, with widespread Moderate HeatRisk. Lower desert highs
are forecast to reach 110-114F, ~3-7 degrees above normal,
through this week with overnight lows remaining quite warm in the
middle 80s to lower 90s. Folks should continue to exercise the
proper heat safety precautions this week, by staying cool,
limiting time outdoors, and staying hydrated.

&&

.AVIATION...Updated at 0045Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
VCTS/TSRA conditions are expected to continue over the next couple
of hours, mainly at KPHX and KIWA. Outflow winds will continue
result in low confidence directions and speeds going into the
overnight hours, but a S-SW component is favored for at least KPHX
and KIWA. Less certainty if a southerly outflow could potentially
reach KSDL and KDVT, so a northerly component wind is favored
going into the overnight hours.

Otherwise, winds are expected to remain westerly or become
variable during the overnight hours prior to early westerly
component winds developing at all terminals tomorrow morning.
Occasional afternoon gusts 20-25 kts will be possible.
Thunderstorm activity is anticipated to remain in the higher
terrain, so the main uncertainty is any outflows that reach the
terminals. At this time, that potential looks low, with a favor
towards and easterly or southeasterly outflow, but there is
currently only a ~10% chance of 35+ kt winds gusts. Skies will
remain BKN through the overnight and into tomorrow due to the
active weather this evening, with improving sky conditions going
into tomorrow night.

Southeast California/Southwest Arizona including KIPL and KBLH:
Southeast winds will be favored at KIPL and south/southwest winds
at KBLH through the period. The threat for thunderstorms looks
again to be confined to higher terrain areas tomorrow, thus there
could be another low potential (10-30%) for outflows to reach both
terminals tomorrow afternoon. Otherwise, skies will remain FEW-
SCT, aside from showers/storms that migrate off the higher terrain
that cause occasional BKN high clouds.

&&

.FIRE WEATHER...
Chances for thunderstorms and wetting rains will increase this
afternoon and evening, particularly over the higher terrain north
and east of Phoenix, as well as in Riverside County, with lesser
chances in the lower elevations. Thunderstorms will be capable of
producing strong erratic outflow winds with up to a 50-70% chance
of outflow winds in excess of 35 mph across South-Central AZ and
parts of Southern CA this afternoon/evening. Through the first
half of the week, thunderstorms and wetting rainfall chances will
be primarily concentrated over the higher terrain of eastern
districts before chances across the lower deserts begin to
increase during the latter half of the week. Gusty outflow winds
will be possible on most days this week exacerbating issues on
any ongoing wildfires and new starts. Otherwise, afternoon upslope
gustiness of 20-25 mph will be periodically common. Min RHs will
be in the 20-30% range today and fall slightly to the 15-20% range
by the middle part of the week.

&&

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

$$

DISCUSSION...Benedict
AVIATION...Young
FIRE WEATHER...Benedict/Smith