546
FXUS65 KPSR 111650
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
950 AM MST Thu Jul 11 2024

.UPDATE...
Updated Aviation

&&

.SYNOPSIS...
Strong high pressure will continue to impact the region over the
next few days allowing excessive heat to persist across the region
through at least Friday. Modest moisture levels will also provide
for chances for isolated thunderstorms over eastern Arizona high
today and gusty winds as far west as the Phoenix area. For Friday
and through the weekend, moisture levels will continue to improve as
rainfall chances eventually spread over the rest of the region.
Temperatures will also gradually cool away from excessive levels and
closer to seasonal normals by Sunday.

&&

.DISCUSSION...
The strong high pressure system currently centered near Las Vegas
continues to be the dominant feature across the region, but day by
day moisture levels are improving and this will eventually curtail
the excessive heat that has been a problem over the last week or so.
Convective activity yesterday was fairly limited in scope and
impacted areas well north and southeast of Phoenix. Increased
moisture levels today are expected to bring a bit more widespread
convection, initially focused along the Mogollon Rim to the White
Mtns. Forecast MUCAPE of around 1000 J/kg across the majority of
southern Arizona along with 20-30kt mid-level winds out of the north
northeast in eastern Arizona should promote isolated strong to
possible severe thunderstorms over the high terrain by mid to late
afternoon. The dry lower levels will again support very high DCAPEs
increasing the strong wind threat. The 00Z HREF generally shows two
main areas of convection, one north northeast of Phoenix and another
over southern Gila County into eastern Pinal and Graham Counties.
Given the expected high CIN in place over the south-central Arizona
lower deserts, any storms coming off the high terrain are expected
to die out quickly, but strong outflow winds moving into the lower
deserts are very likely. Guidance generally supports the strongest
outflow winds across central Pinal County with another likely weaker
outflow potentially moving southwestward into northern Maricopa
County.

Moisture levels will continue to improve into Friday, especially
across the lower deserts as guidance shows a robust Gulf moisture
surge occurring tonight/Friday morning. Convective potential over
the higher terrain for Friday seems to be very similar to today
minus less activity in far southeast Arizona due to a pocket of
drier air moving out of west Texas and northern Mexico. The chance
for strong to severe storms on Friday looks to be considerably lower
due to lower instability and DCAPEs, but better moisture and lower
CIN over the lower deserts may be enough for some storms to survive
or to develop along propagating outflows into the south- central
Arizona lower deserts.

Excessively hot temperatures will persist through at least Friday
with highs gradually lowering each day as lower level moisture
increases. Forecast highs today are again between 112-116 degrees in
the Phoenix area to 114-119 degrees across the western deserts
before some improvement is seen on Friday across the western
deserts. Surface dew points increase a good amount into Saturday
with readings in the 60s across the western deserts to the mid to
upper 50s in the Phoenix area. Forecast highs Saturday do take a
decent step lower with readings mostly between 110-113 degrees, but
given the increased humidities it really won`t feel any cooler than
Friday. The one upside starting Saturday is there should be some
cloud cover at times and this could help to take the edge off the
heat.

Forecast confidence for convection over the weekend has decreased as
model guidance is now shifting the expected development of an upper
level low from over New Mexico to over Texas. Guidance is now also
hinting at a quiet day across at least southeast Arizona on Saturday
due to the pocket of drier air, despite our flow turning solidly out
of the east. An easterly flow is almost always favorable for monsoon
activity, but given the models shifting toward a brief period of
drying into eastern Arizona Saturday`s convection is probably going
to be fairly limited. Moisture advection should improve once again
Saturday night into Sunday across the entire area creating better
storm chances later Sunday, but likely losing support of the upper
low (now probably too far east) may hinder widespread development.
However, with deeper moisture likely in place by Sunday afternoon,
as long as the higher terrain convection is widespread enough, any
colliding outflows over the lower deserts should result in
additional development. Locally heavy rainfall may also become a
concern on Sunday along with a strong wind threat from any stronger
storms that may develop. Drier air is expected to gradually spread
from west to east early next week likely limiting convection to
south- central and eastern Arizona by Tuesday. Temperatures are also
expected to continue to improve Sunday into Monday with highs
falling below 110 degrees over the south-central Arizona lower
deserts to around 110 degrees over the western deserts. If guidance
is correct in showing the drier air by next Tuesday or Wednesday,
then that should eventually push temperatures up a few degrees
during the middle of next week.

&&

.AVIATION...Updated at 1135Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The potential for multiple strong, gusty outflow boundaries with
abrupt wind shifts are the primary weather hazards this evening.
Confidence is very good that light east winds will turn to a W/SW
direction around noon, however forecast uncertainty grows
exponentially thereafter. While actual thunderstorms should remain
well removed from the Phoenix metro, outflows emanating from the
east, north, and south could all impact operations. The most likely
direction will initially be from the east due to afternoon storms
over southern Gila/eastern Pinal counties with a 30% chance of
prolonged wind gusts over 30kt. Onset timing is also somewhat
uncertain with a range of 00Z-03Z among high resolution models.
There is also a non-zero chance of a northerly outflow also sweeping
into the metro, however odds are low enough not to include in this
TAF package. Higher odds exist for a wind shift to the S/SW mid/late
evening as storms in southern AZ could push an outflow north.
Confidence is slightly better overnight that an easterly component
will finally settle over the metro sometime after midnight.


Southeast California/Southwest Arizona including KIPL and KBLH:
The potential for increasing wind speeds overnight will be the main
weather issue through Friday afternoon with occasional SCT mid/high
level cloud decks. S/SE winds will be preferred through the entire
TAF period, however a Gulf surge overnight may cause an increase in
speeds and frequent gusts. Onset timing looks to be around or just
prior to midnight, with the greatest uncertainty in the magnitude
and duration of any stronger gusts.

&&

.FIRE WEATHER...
Unusually hot weather will persist the next few days with
thunderstorm activity steadily increasing over eastern districts.
Moisture will steadily increase over most districts through the
weekend allowing temperatures to retreat while humidity levels and
rainfall chances increase markedly. Storms will initially produce
only isolated wetting rain chances in eastern districts with areal
coverage likely becoming far more widespread by the weekend. Minimum
humidity values will continue to fall into a 5-15% range through
Friday, however by Sunday, values should struggle to fall below 20%.
Some slight drying may wash over the districts by the middle of next
week when minimum values fall closer to a 10-20% range. Occasional
afternoon upslope gusts near 20 mph will be common the next few
days, and the increase in thunderstorm activity will produce more
frequent strong outflow winds across a larger expanse.

&&

.CLIMATE...

Record Highs

           Phoenix      Yuma      El Centro
          ---------    -------   -----------
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...18
FIRE WEATHER...18/Kuhlman
CLIMATE...Berislavich/Kuhlman