933
FXUS65 KPSR 100936
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
236 AM MST Wed Jul 10 2024

.SYNOPSIS...
Strong high pressure will allow extreme heat to persist across the
region for another few days as many high temperature records will
be threatened. Moisture will also slowly move back into the area
providing modest chances for isolated thunderstorms over eastern
Arizona high terrain. Over the weekend, far better moisture should
be imported into lower elevations supporting improved rainfall
chances, as well as pulling temperatures away from excessive
levels and closer to seasonal normals.

&&

.DISCUSSION...
There was some improvement with atmospheric moisture yesterday as
a patch of mid level moisture tracked southeastward out of Nevada
into northern and central Arizona by the afternoon. This allowed
for a bit more widespread and stronger convection than models
advertised. However, the strong high pressure system remains
intact over the region with the center now positioned over Nevada.
The high has weakened slightly, but the expansive heat dome that
it helped to create remains in place with daily highs still
reaching near or even exceeding records. Guidance continues to
support little overall change with heights and temperatures over
our area through Friday as the high center very slowly drifts
eastward into Utah. Excessive heat will remain the main forecast
concern today through Friday with highs through Thursday ranging
from 114-120 degrees across the western deserts to 112-117 degrees
across the lower deserts of south-central Arizona.

Convective activity today is expected to be less vigorous across
the higher terrain east of Phoenix as some drier air will work
southward into eastern Arizona. However, the HREF still indicates
some modest convection developing in the mountains north of
Phoenix this afternoon, likely sending gusty outflow winds into at
least the northern portion of Phoenix early this evening. Moisture
is then expected to increase again across southeast Arizona into
the higher terrain east of Phoenix on Thursday leading to more
widespread and stronger thunderstorm activity. Forecast soundings
for Thursday afternoon show modest MUCAPE up to around 1000 J/kg
along the Mogollon Rim extending into the foothills just east of
Phoenix. This instability along with plenty of dry air in the
boundary layer supporting high DCAPEs should result in good
potential for strong to possibly a few severe thunderstorm wind
gusts over the high terrain northeast and east of Phoenix. SPC has
introduced a Marginal risk for severe storms on Thursday with the
area encompassing much of area east of Phoenix and probably too
optimistically westward into the Phoenix metro. Moisture levels
over the south-central Arizona lower deserts are not likely to be
high enough for additional redevelopment of storms into the
Phoenix metro, but strong outflow winds from the east southeast
are much more likely to occur. The 00Z HREF shows the threat for
strong winds maximized over Gila County into eastern Pinal County,
but it still shows upwards of a 50% probability of 30+ kt winds
reaching Phoenix and a 10% probability of 50+ kt winds. However,
just looking at the new 06Z HRRR, it barely shows any convection
east of Phoenix Thursday afternoon and virtually no outflow winds
getting near Phoenix. It will be something to monitor over the
next day and a half.

Friday still looks to be a transition day for our area as the high
center is finally far enough to the north and east that easterly
flow will overtake the area. Moisture advection will be much
better starting Thursday night as a strong Gulf surge is expected
to occur. Between the Gulf surge and easterly moist flow starting
Friday morning, there should be a noticeable change in boundary
layer moisture. Temperatures will react to the higher moisture,
but Friday`s forecast highs are still expected to range from
112-116 degrees over the lower deserts. The higher moisture
content air on Friday may allow for some convection over higher
terrain areas south of Phoenix as well as over the eastern Arizona
high terrain. However, convective potential into the south-
central Arizona lower deserts should still be limited with PoPs
generally at between 10-15%.

An additional surge of moisture off Gulf of California is expected
Friday night/Saturday morning along with the continued moist
advection out of New Mexico. This is likely to increase PWATs
across the lower deserts into a 1.2-1.5" range on Saturday,
potentially allowing for lower desert convection developing off of
any outflows from higher terrain areas. Temperatures Saturday are
expected to continue to improve with readings dropping to between
107-111 degrees over most of the lower deserts. However, despite
the lower air temperatures Saturday, the increased humidity is
likely to still make it feel uncomfortably hot.

The best potential for more widespread and potentially strong
monsoon thunderstorm activity looks to be on Sunday when models
continue to show upper level support from an upper level low that
develops over New Mexico. This potential could carry over into
early next week as the low is forecast to remain just east of
Arizona, but as with active periods during the monsoon it is
common to have a down day after a very active day due to
convective overturning of the atmosphere. Starting Tuesday, an
upper level trough is forecast to reach California, while the sub-
tropical high center may shift back closer to or even into
Arizona. This somewhat favored scenario would point toward some
drier air working back into the region from the west during the
middle of next week and thus pushing most of the monsoon activity
back over the eastern Arizona high terrain. At least for now if
this does occur, guidance generally supports the ridge not being
nearly as strong as it currently is and keeping temperatures
closer to normal readings through the rest of next week.

&&

.AVIATION...Updated at 0542Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation weather concerns are expected through the TAF
period. Winds will continue to follow diurnal tendencies with
extended periods of light and variable winds at times. Occasional
afternoon breezes gusting upwards of 20 kts are expected again for
Wednesday. Uncertainty increases heading into early Wednesday
evening as hi-res guidance indicate the potential for isolated
strong storms north of Phoenix to send an outflow toward the south
into the Valley. Have added mention in the SDL and DVT TAFs for
now, but exact magnitude is uncertain. Mostly clear skies with a
few mid and high clouds will continue throughout the period.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns are expected through the next 24
hours. Winds will favor the E to SE at KIPL, while winds at KBLH
will favor the S. Wind speeds will generally climb to upwards of
8-12 kts through the period. Mostly clear skies will persist.

&&

.FIRE WEATHER...
Unusually hot weather will persist over the next few days with
thunderstorm activity increasing over eastern districts starting
Thursday. Today`s activity should be quite isolated with more
widespread activity over the higher terrain Thursday followed by
chances spreading into the lower deserts on Friday. However,
chances of wetting rainfall will mainly stay confined to southern
Gila Co. Minimum humidity values over the lower deserts will
continue to fall into a 5-10% range through Thursday, improving to
10-15% Friday, with somewhat higher values over the Arizona higher
terrain. Occasional upslope gusts near 20 mph will be common, and
with increased thunderstorm activity, stronger outflow winds will
gradually become more likely Thursday afternoon/evening. Far
better chances for beneficial rainfall arrive over the weekend
with activity moving into lower elevation locations.

&&

.CLIMATE...

Record Highs

           Phoenix      Yuma      El Centro
          ---------    -------   -----------
July 10   115 (1958)  118 (1959)  116 (2021)
July 11   118 (1958)  118 (1958)  117 (1975)
July 12   116 (2020)  119 (1939)  118 (1964)

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Friday for AZZ530>555-559.

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

&&

$$

DISCUSSION...Kuhlman
AVIATION...Smith
FIRE WEATHER...Kuhlman
CLIMATE...Berislavich/Kuhlman