234
FXUS65 KPSR 121758
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1058 AM MST Fri Jul 12 2024

.UPDATE...
18Z Aviation Discussion.

&&

.SYNOPSIS...
A strong ridge of high pressure located over the Great Basin will
continue to result in excessive heat through Saturday. This ridge
will finally migrate over the 4-Corners region this weekend,
resulting in a slow cooling trend and a noticeable increase in
moisture levels. Isolated showers and storms will be possible
across south-central Arizona through Saturday with the best
chances for storms reaching the lower deserts on Sunday. Drier
conditions are expected to gradually spread over the area during
the first half of next week.

&&

.DISCUSSION...
The strong high pressure ridge is still the most dominant feature
across the region, but moisture continues to increase day by day
allowing for increasing convection. The heat dome which has caused
excessive heat all week will remain intact today and largely even
through Saturday. Forecast highs for today are a couple degrees
cooler than what we have been seeing over the past week, but they
still easily reach excessive heat levels. PWATs have improved to
over 1" across much of the lower deserts, but drier air working in
from northern Mexico is lowering PWATs to around 0.8" across
eastern Arizona. Despite the minimal moisture levels for today,
the excessive heat will again create steep lapse rates with
MUCAPEs mainly between 500-750 J/kg from the White Mtns through
the Mogollon Rim. Higher CAPE is forecast across southwest Arizona
and southeast California today, but that will be wasted due to
strong CIN. The latest HREF and the 06Z HRRR show convection
forming over the higher terrain east and northeast of Phoenix this
afternoon with a east southeasterly steering flow mostly keeping
the convection riding just north of Phoenix into this evening.
The HREF does show some potential for additional convective
development across Pinal County this evening, probably from
colliding outflows, but this is of fairly low forecast
confidence. The gusty wind threat today looks to be considerably
lower than what we had yesterday due to lower instability, less
mid-level flow, and marginally lower DCAPEs.

Lower level moisture will continue to improve Friday night into
Saturday causing surface dew points to surge to around 70 degrees
in Yuma and El Centro to around 60 degrees in the Phoenix area.
Lingering overnight clouds Friday night are also likely to keep
temperatures very warm, likely the warmest night of this past
week. Forecast highs Saturday do drop another 3 degrees or so from
today`s highs, but given the increased humidities, it will still
feel just as hot as Friday. Even though temperatures fall enough
on Saturday to drop the HeatRisk mostly into the Moderate
category, we feel it was necessary to extend the Excessive Heat
Warning through Saturday due to Heat Indices essentially staying
between 110-115 degrees. Convective potential for Saturday still
looks to be rather limited due to the drier air temporarily
working its way into far eastern Arizona, but since moisture will
have worked its way all the way through southern California we
can`t rule out some isolated showers and thunderstorms over the
western deserts, especially within JTNP and over any locally
higher terrain features. Hi-res CAMs generally agree on most of
the convection staying over the higher terrain north of Phoenix
with some potential for some activity across Pima County and
southern Maricopa County.

Deeper moist southeasterly flow is then expected to overtake the
majority of Arizona late Saturday into Sunday increasing PWATs to
around 1.5" over the lower deserts. Higher moisture will also
spread across eastern Arizona which will provide for much more
expansive higher terrain development Sunday afternoon and likely
multiple outflows into the lower deserts prompting further
development of convection. NBM PoPs for Sunday rise to 30-40%
across the south-central Arizona lower deserts to 50-60% over
higher terrain areas east of Phoenix. GFS forecast soundings for
Phoenix show considerable CAPE at around 1500 J/kg Sunday
afternoon, but with still some modest CIN in place. However,
given the potential for high instability any deep storm outflows
or colliding outflows will likely be enough for lower desert
convective development. Any strong thunderstorms Sunday will
likely have the potential to produce strong to possibly severe
wind gusts and locally heavy rainfall.

Temperatures Sunday should lower enough to fall below excessive
heat levels across the board due to the overall increased
moisture, convective activity, and additional cloud cover.
Starting Monday, guidance is still showing some drier air working
from west to east through southern California into at least
western portions of Arizona. There should still be enough
moisture to work with across the eastern half of Arizona for
another round of shower and thunderstorm activity on Monday, but
instability is likely to be lower and thus the convective
potential should be noticeably lower than Sunday. The drier air
should then continue to spread eastward Tuesday into Wednesday
mainly limiting any convection to the eastern Arizona high
terrain. Temperatures should bottom out on around Monday, but
highs are still forecast to be 2-4 degrees above normals. As the
drier air works through the region during the middle part of next
week, temperatures should slowly rise with highs likely topping
110 degrees over much of the lower deserts by next Wednesday or
Thursday.

&&

.AVIATION...Updated at 1740Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
There is a lot more uncertainty regarding thunderstorm potential
this afternoon and evening. Latest guidance suggests lower storm
coverage across the region and therefore less confidence in
outflow boundaries reaching KIWA and KPHX (10% chance). However
there still around a 30% chance of a northerly or northeasterly
outflow reaching KSDL and KDVT tonight, mainly after 03Z. Winds
through the rest of today will be slow to veer, becoming westerly
by 23Z-00Z. Winds should return out of the ESE by 09Z-10Z tonight.
Cloud cover is expected to remain FEW to SCT throughout the
period. Smoke from nearby fires could create haze and slantwise
visibility issues through early this afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns are expected through the next
24 hours. Winds will continue to favor an E to SE component at
KIPL, while a southerly direction is expected at KBLH. Gusts will
materialize this afternoon to around 20-25 kts at both sites.
Otherwise, FEW-SCT mid to high clouds will continue throughout
the period.

&&

.FIRE WEATHER...
Very hot temperatures will be seen again today with thunderstorm
chances steadily increasing over the eastern districts through the
weekend as moisture improves. Temperatures will slowly retreat
over the weekend while humidity levels increase. Storms will
initially produce only isolated wetting rain chances in eastern
districts with areal coverage likely becoming far more widespread
by Sunday. Minimum humidity values will fall to around 10-15%
today, 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 12   116 (2020)  119 (1939)  118 (1964)

&&

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

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

&&

$$

DISCUSSION...Kuhlman
AVIATION...Salerno
FIRE WEATHER...Salerno/Kuhlman
CLIMATE...Kuhlman