416
FXUS65 KPSR 141158
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
458 AM MST Sun Jul 14 2024

.UPDATE...Updated 12Z Aviation Discussion...

&&

.SYNOPSIS...
Thunderstorm chances will increase today with the potential for
some activity to get to the Valley floor. Strong winds and
localized dense blowing dust will be the primary concerns with
these thunderstorms. Thunderstorm chances will then become mostly
confined to the higher terrain through at least the first half of
the week before chances increase across the lower deserts for the
second half. Temperatures through the week will remain above
normal with widespread Moderate to locally Major Heat Risk.

&&

.DISCUSSION...
Early morning satellite and radar showed a decaying thunderstorm
complex over northern Sonora with isolated to scattered new
thunderstorm development occurring along the international border
in southern Arizona. Elsewhere across the forecast area, quiet
conditions are in place with a gulf surge helping to boost dew
points into the 60-70 degree range across much of central Arizona
to southeast California. The aforementioned decaying northern
Sonora thunderstorm complex will also act to increase moisture
into southern Arizona. Meanwhile, objective analysis showed an
upper level ridge centered near the Four Corners region with 500
mb heights around 594 dm. Temperatures today are forecast to be
around 2-5 degrees cooler than yesterday due to the increase in
moisture into the region along with the gradual weakening of the
ridge. Lower desert highs today will top out in the 106-111 degree
range for most places. However, the increased moisture will help
push heat indices to upwards of 113-115 degrees across southeast
California and the Lower Colorado River Valley. Thus, an Excessive
Heat Warning remains in effect through this evening for the areas
mentioned.

The increase in better boundary layer moisture and higher
instability will provide better thunderstorm chances to south-
central Arizona heading into this afternoon and evening. Ensemble
guidance show PWATs continuing to rise to around 1.3-1.5" today and
forecast soundings and HREF data showing CAPE values increasing to
around 1000-1500 J/kg. DCAPE values will also be high at around 1500-
2000 J/kg, which will support strong to potentially severe winds
and long traveling outflows. HREF paintball plots show convection
firing up this afternoon in southeast Arizona near the international
border and along the Rim. These thunderstorms are then expected
to send outflows traveling toward central Arizona, though there is
uncertainty in exactly how strong these outflows will be and
whether or not new convection will fire along them. Some of the
hi-res guidance has backed off on convection getting into the
lower elevations of south-central Arizona with modest CIN in
place. However, strong, colliding outflow boundaries could
certainly invigorate shower and thunderstorm activity across parts
of the lower deserts this evening. As mentioned before,
thunderstorms will be capable of producing strong winds with 00Z
HREF probabilities for winds in excess of 35 mph climbing upwards
of 50-70%, particularly across southern Gila County. Strong
outflows will be capable of producing areas of dense blowing dust
in dust prone regions, which can quickly reduce visibilities and
make travel dangerous. Locally heavy rainfall will be possible for
areas that end up under thunderstorms and could lead to an
isolated flooding concern.

Going into the first part of the new workweek, moisture in the
region will slightly decrease while subsidence over the area
increases as the ridge center migrates over Arizona. The latest
global ensemble runs have backed off on the amount of drying that
will take place in the atmospheric column early to midweek with
ensemble mean PWATs sticking around 1.3-1.5". Daily thunderstorm
chances will continue across the Arizona high terrain through the
upcoming week with chances increasing across the lower elevations
during the latter half of the week as moisture increases. Aside from
thunderstorm chances, temperatures will once again approach or
exceed 110 degrees for many areas across the lower deserts by the
middle part of the week. With these temperatures, some areas could
flirt with excessive heat conditions, particularly across southeast
California where there are pockets of Major HeatRisk. Elsewhere,
most places will be under Moderate HeatRisk. Folks should continue
to exercise the proper heat safety precautions this week, including
staying cool, limiting time outdoors, and staying hydrated.

&&

.AVIATION...Updated at 1155Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The potential for thunderstorm activity as well as outflow winds
will be the primary weather issues heading into this evening.
Westerly winds will continue through most of the day. There
continues to be some lingering gusts near 20 kts, however, that is
expected to subside during the next couple of hours with speeds
generally aob 12 kts through this afternoon. Heading into this
evening, thunderstorms are likely to develop across the higher
terrain areas to the north and east of the metro. Confidence
continues to remain low on the overall convective coverage across
the area and as a result there is no mention of VCTS/TSRA for this
TAF package but may need to be included in subsequent packages if
confidence for greater coverage increases. What is a bit more
certain is the potential for outflow winds to impact the
terminals, most likely from the north to northeast between the
03-05z timeframe. There is a 30-50% chance of gusts exceeding 30
kts with the outflow. Sky coverage through this afternoon will
generally remain FEW, increasing to SCT-BKN this evening depending
on the overall convective coverage.


Southeast California/Southwest Arizona including KIPL and KBLH:
Southeast winds will be favored at KIPL while south winds will be
favored at KBLH through the period. Thunderstorms are likely to
develop over the higher terrain areas, especially over the San
Diego Mountains later this afternoon. This could result in some
outflow winds, especially at KIPL where a TEMPO for westerly wind
gusts is in place. Otherwise, periodic gusts into the 20-25 kt
range are likely at both sites, especially this afternoon and
evening. FEW-SCT passing mid to high level clouds will prevail
through the period.


&&

.FIRE WEATHER...
Chances for thunderstorms and wetting rains will increase this
afternoon and evening, particularly over the higher terrain east of
Phoenix 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 southern
Gila County 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
many 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 15-25%
before decreasing to around 10-20% by the middle part of the week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST this evening for AZZ530.

CA...Excessive Heat Warning until 8 PM PDT this evening for
     CAZ560>570.

&&

$$

DISCUSSION...Smith
AVIATION...Lojero
FIRE WEATHER...Smith/18