396
FXUS65 KPSR 291024
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
324 AM MST Sat Jun 29 2024

.SYNOPSIS...
Above normal temperatures will persist well into next week,
especially across the western deserts. Expect daily high
temperatures around 110 degrees across the lower deserts this
weekend before temperatures cool slightly across south-central
Arizona starting Monday. After an overall quiet day today, shower
and thunderstorm chances will ramp up later on Sunday across
south-central and eastern Arizona. The increased monsoon moisture
starting Sunday should last into the middle of next week giving
daily chances of showers and thunderstorms to portions of southern
and central Arizona.

&&

.DISCUSSION...
Dry air continues to dominate the western half of Arizona and
southern California, while modest monsoon moisture stubbornly
remains in place across the southeastern 1/3rd of Arizona. The
weaker ridge yesterday resulted in barely any CIN and the
instability driven by the lingering moisture allowed for fairly
widespread showers and thunderstorms across Pinal County through
southeast Arizona. For today, the sub-tropical ridge center over
the Southern Plains is forecast to strengthen while also extending
back through our region. This added subsidence aloft should be
enough to create an overall fairly quiet day across the area. Hi-
res CAMs do show some isolated convection popping up this
afternoon across far southern Maricopa County and over the higher
terrain in Gila County, but the coverage should be considerably
less than what was seen on Friday.

Over Mexico, an easterly wave can be seen within water vapor
imagery early this morning and this is expected to drive a robust
MCS across Sonora later today before nearing southeast Arizona
tonight. This wave will help to turn our mid level flow out of
the southeast tonight, allowing for moisture to surge
northwestward into southern and central Arizona. We may also see
some isolated elevated light shower activity late tonight into
early Sunday morning associated with this moisture advection and
any gravity waves emanating from the Sonoran MCS.

Guidance continues to point toward a very busy monsoon day across
southeast Arizona Sunday afternoon where instability is likely to
be maximized and then potentially Sunday evening into south-
central Arizona. The 00Z HREF and now the latest HRRR all point
toward outflows and at least some showers and thunderstorms
progressing northwestward out of the Tucson area by early Sunday
evening. Forecast MUCAPE does decrease to around 500-750 J/kg in
the Phoenix area with the axis of better instability extending
toward Tucson. Forecast soundings do show some CIN in the Phoenix
area, but any large robust outflow and/or continuous
redevelopment of convection should be enough to overcome the
expected CIN. As of right now, we are confident there will be at
least some scattered showers and thunderstorms making their way
into south-central Arizona Sunday evening with the best chances
over Pinal and Gila Counties with PoPs of 50-60%. Lower chances
of 30-40% are expected into the Phoenix area as the activity
begins to enter lower instability and higher CIN. A few storms are
likely to be strong to severe with damaging winds possible. Storm
outflows should also have a good possibility of generating some
blowing dust, especially in Pinal County. Moisture levels should
also be ample enough with PWATs increasing toward 1.75" to provide
for some localized heavy rainfall and potentially some minor
flooding.

The GFS has been consistently showing an MCV forming Sunday night
over south-central Arizona with the remnant MCV slowly drifting
toward Flagstaff on Monday. Guidance does overall agree with
Monday showing a much quieter monsoon day, likely partially due to
the subsidence behind the MCV and because the flow will begin to
turn southwesterly again. This southwesterly flow should provide
for a brief period of drying Monday into Tuesday, but moisture
should still remain plenty adequate on Tuesday for some mainly
high terrain based showers and thunderstorm activity. Forecast
confidence for Tuesday and Wednesday is still somewhat low due to
the lack of any good forcing as we will fall in between a
developing high pressure ridge off the coast of California and the
ridge center over the Lower Mississippi Valley. A couple of weak
upper level shortwave troughs are also expected to pass by to our
north Tuesday and Wednesday with potentially a little bit of upper
level forcing over Arizona on Wednesday. This may help with some
convection, but a southwesterly steering flow is generally not
very favorable for convection impacting the lower deserts. Later
next week, a very strong high pressure ridge with H5 heights
upwards of 598dm is forecast to shift into California by Thursday
and maybe into the Great Basin or over our region by the
following weekend. This synoptic set up would bring northerly dry
flow across our region considerably limiting monsoon activity
starting Thursday.

Temperatures over the next week or so are expected to stay several
degrees above normal, particularly across the western deserts.
Forecast highs up to around 110 degrees are likely to be seen
across the south-central Arizona lower deserts to 108-113 degrees
across the western lower deserts. When adding in fairly high dew
points in the 50s to the expected highs around 110 degrees over
much of the area, the heat will continue to be dangerous to those
most vulnerable and to those not adequately prepared for the heat.
An Excessive Heat Watch remains in effect for portions of
southeast California and the Lower CO River Valley for the
majority of next week.

&&

.AVIATION...Updated at 0548Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

A broad swath of southerly outflow winds originating from earlier
storms that were over Pinal and Pima Counties has overspread the
Valley floor. Expect southerly breeziness (gusts to 20kts) to
slowly weaken and become light and variable favoring southeasterly
before sunrise. Expect SW/Wly winds to develop by mid afternoon.
Anticipate an increase in high clouds late tonight and Saturday
morning. As for storm development Saturday afternoon/evening,
confidence in impacts at the TAF sites too low to reflect in the
forecasts at this time.

Southeast California/Southwest Arizona including KIPL and KBLH:

Overall, expect familiar warm season wind patterns at the TAF
sites through Saturday. At KIPL, westerly winds will shift to
southeasterly by sunrise. At KBLH, SWly winds early in the TAF
period will trend to southerly by 09Z or so. Southerly breeziness
(gusts to 25kts) resumes around midday Saturday. Otherwise,
expect clear skies.

&&

.FIRE WEATHER...
Very limited monsoon activity is expected today before fairly
widespread showers and thunderstorms are expected over south-
central and eastern Arizona Sunday afternoon and evening. Humidity
levels today will drop slightly from yesterday with MinRHs in the
upper teens across the lower deserts to 20-30% over the higher
terrain with only very slight improvement through Sunday
afternoon. Overnight recoveries will be fair tonight and good
Sunday night as moisture increases over much of the area. Winds
will follow typical diurnal trends through Sunday afternoon with
occasional afternoon breeziness near 20 mph, while strong outflow
south southeasterly winds look likely Sunday evening into south-
central Arizona. Daily monsoon storm chances should persist
through at least south-central Arizona into the middle part of
next week, while humidities rebound to 20-25% across the lower
deserts to upwards of 35-40% over the eastern Arizona high
terrain. Temperatures next week will remain several degrees above
normal each day.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Watch from Sunday morning through Friday evening
     for AZZ530.

CA...Excessive Heat Watch from Sunday morning through Friday evening
     for CAZ562-566-567-569-570.

&&

$$

DISCUSSION...Kuhlman
AVIATION...AJ
FIRE WEATHER...Kuhlman