531
FXUS65 KPSR 141710
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1010 AM MST Sun Jul 14 2024

.UPDATE...
Updated Aviation

&&

.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 1710Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Thunderstorms and at least one outflow boundary causing gusty winds
with abrupt wind shifts will be the main weather impacts through
tonight. Confidence is excellent that west winds with occasional
modest gusts near 15kt will prevail into the early evening hours
with only mid/high clouds decks. Thunderstorms are likely to develop
across higher terrain areas well northeast of the terminals by late
afternoon, however forecast confidence is relatively low with
respect to how far into the metro storms can survive/re-form during
the evening hours.

At this time, there is enough evidence suggesting storms skirting
the northern edge of the Phoenix airspace to include VCTS mention
for KSDL/KDVT. Outflows with abrupt wind shifts appear far more
likely across the entire area with better than a 50% chance of some
northerly component incorporating gusts around 30kt during a 03-05Z
time frame. Wind directions thereafter become tied to locations of
storms and additional wind shifts are likely, though timing and
magnitude remain very uncertain. Should several more intense
outflows happen to collide within area, there could be more direct
thunderstorms impacts for all terminal locations, however current
odds are less than 20% and preclude stronger mention in this TAF
package.


Southeast California/Southwest Arizona including KIPL and KBLH:
Wind gusts with shifting directions will be the greatest weather
concern through Monday morning under occasional midlevel cigs. While
southeast winds will be favored at KIPL and south winds at KBLH,
there may be wind shifts due to outflow boundaries from nearby
thunderstorms. Thunderstorms are possible this afternoon over the
higher terrain areas west of KIPL which could result in gusty W/SW
outflow winds surging into lower elevations. Gusts over 25kt would
be most likely at KIPL late afternoon/early evening with lesser
probabilities at KBLH. There is around a 15% chance of TSRA directly
impacting KIPL this afternoon, and radar trends will need to be
monitored.

&&

.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...18
FIRE WEATHER...Smith/18