Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 190019
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
519 PM MST Mon Mar 18 2024

.UPDATE...Updated 00Z Aviation Discussion.

&&

.SYNOPSIS...
Unsettled weather continues with showers and thunderstorms
expected through the remainder of this afternoon and early evening
across south-central Arizona. Coverage of showers and
thunderstorms decreases for Tuesday before the responsible weather
system finally exits the region Wednesday. Ridging will build
over the Intermountain West by the end of the week which will
result in dry and tranquil conditions along with continued
temperature increases towards well-above normal levels. Cooler
unsettled weather then looks to return this weekend into early
next week.

&&

.DISCUSSION...
An active afternoon is underway as showers and thunderstorms
continue to develop across parts of central Arizona with strong
winds, hail, locally heavy rainfall, and frequent lightning
possible through the afternoon. The threat for strong and perhaps
isolated severe thunderstorms will continue through the remainder
of the afternoon into the early evening.

The unsettled weather pattern continues as a Rex Block remains in
place over the western CONUS with a cutoff upper-level low situated
over the Southwest. Currently this afternoon, satellite WV imagery
shows this upper low continuing to retrograde westward with the
low center now situated over Riverside County. As a result, an
influx of better moisture has creeped into south-central Arizona
with PWAT values increasing upwards of 0.6-0.7" through the
afternoon. Instability across the region continues to increase
this afternoon with the latest SPC mesoanalysis showing SBCAPE
values in excess of 500 J/kg and steep mid-level lapse rates
around 8 C/km across Maricopa, Pinal, and Gila Counties. Combined
with forced ascent associated with the aforementioned upper low,
thunderstorms will continue to blossom across parts of south-
central Arizona through the afternoon. The latest 12Z HREF keeps
the bulk of this thunderstorm activity east of Phoenix through the
afternoon with chances decreasing westward over the desert floor.
However with the potential for strong outflows pushing across the
valley floor this afternoon into the early evening, we could
conceivably see some additional development make it into the
Valley. As mentioned, strong outflows will be possible today with
model soundings showing DCAPE values upwards of 700-900 J/kg this
afternoon. HREF shows probabilities of exceeding 35 mph climbing
upwards of 50-70% with the greatest chances residing across
eastern Maricopa and Pinal Counties and portions of southern Gila
County. Could see an isolated severe thunderstorm gust, which the
HRRR has been aggressive in showing in some of its runs.
Additionally, the better lapse rates and instability could lead to
some larger hail compared to the small pea-sized hail that`s been
more common in some of our recent events. In terms of dust, some
areas of blowing dust generated by strong outflows will be
possible, though less favorable given the expected orientation of
outflow boundaries. Rainfall amounts outside of thunderstorms will
generally remain light, mostly under 0.25" with locally heavy
amounts for areas that end up under a thunderstorm.

The upper low will shift eastward back over Arizona Tuesday while
gradually weakening in the process. Instability will not be as high
as today with SBCAPE values around 100-300 J/kg closer to the cold
core. CAMs support isolated to scattered showers and thunderstorms
developing tomorrow afternoon around the Kofas and over high terrain
areas north and east of Phoenix. The Rex Block pattern finally
breaks down heading into Wednesday and the upper low shifts east
into New Mexico. This will be replaced with flat ridging over the
Desert Southwest giving us drier, warmer weather for the latter half
of this week. Temperatures by Thursday warm up into the low to mid
80s across the south-central Arizona lower deserts and mid to upper
80s across southeast California and southwest Arizona. Some areas
will flirt with their first 90 degree temperature of the year on
Thursday with NBM probabilities of reaching or exceeding 90 degrees
climbing upwards of 50-70% across the Imperial Valley. Global
ensembles then show troughing returning to the western CONUS this
weekend into early next week. Thus, we will be looking at the
return of some cooler unsettled weather once again.

&&

.AVIATION...Updated at 0015Z.

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

Scattered showers and thunderstorms are currently moving through
eastern and northern portions of the Phoenix Metro. These storms
are anticipated to fall apart and exit the Phoenix Metro between
02-03Z. In the meantime, theses storms, along with their
outflows, are causing easterly gusts around 20-25 kt with
occasional gusts of 20-30 kt. Once these storms fall apart and
exit the Metro, the winds will also start to calm, although some
gusts to around 15-20 kt may hang on through 04-05Z, mainly for
the northern terminals (KDVT & KSDL). Winds are expected to go
light, aob 5 kt, and variable for the overnight hours, however
they may predominantly be out of the east. By mid-morning the
winds will become easterly before doing their typical diurnal
switch to the westerly tomorrow afternoon. SCT-OVC cloud bases are
currently around 6-8 kft with these showers and storms. Once they
fall apart and exit the Metro, clouds will scatter out and start
to lift with FEW-SCT high clouds expected for the overnight hours.
Then FEW clouds with bases aoa 7-9 kft are expected for tomorrow
afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation weather concerns are expected through the
forecast period. Light and variable winds at KBLH will become
northwesterly late this evening and then transition to
northeasterly late tomorrow morning. At KIPL, current light
westerly winds will become northwesterly late tomorrow morning.
Wind speeds at both terminals will be aob 5 kt through the TAF
period. FEW-SCT high clouds are anticipated through the TAF
period. With FEW CU clouds developing tomorrow afternoon with
bases aoa 8 kft.

&&

.FIRE WEATHER...
Low pressure will continue to promote rain chances over the next
few days, especially across higher elevation locations. Outside of
any rainfall activity, breezy conditions are expected across the
the far eastern districts with max gusts approaching 30-35 mph at
times. Elsewhere, winds should generally be light, with occasional
afternoon breeziness. High pressure will then build over the
region by the middle of the week resulting in drier and more
tranquil conditions. MinRHs for the front half of the week should
remain above 20-25% across the region before moisture levels
begin to drop off once the aforementioned high pressure sets in.
Temperatures will hover around normal for the next few days before
a quick warm-up takes place during the latter portion of the week

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...Smith
AVIATION...Berislavich
FIRE WEATHER...RW


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