Severe Thunderstorm Warning 76, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
1224 PM MST Fri Aug 12 2022

.SYNOPSIS...
Today and through the weekend will bring increased chances for
monsoon storms. Storm activity will tend to favor the afternoon
and evening hours with strong winds, heavy rainfall, and localized
flooding all possible. A Flood Watch is in effect today through
11 pm MST/PDT for all of south-central and southwest Arizona, as
well as southeast California. Slightly cooler temperatures are
expected over the weekend with increased cloud cover. Chances for
showers and thunderstorms will persist into early next week.

&&

.DISCUSSION...
Very broad high pressure centered over the plains is resulting in
east-southeast flow across our region, which is aiding in keeping
a very moist atmosphere in place. Precipitable water values
exceed 1.5 inches across most of our forecast area, with the
greatest moisture in southwest Arizona. An MCV has also been
moving through this area, resulting in scattered showers and
isolated thunderstorms. This feature will continue to play a key
role this afternoon and evening as it continues to move through
our western CWA. There is also another MCV circulating along the
Arizona/Mexico border that looks to be another key player in this
afternoon and evenings weather.

Plenty of sunshine across most of our forecast area today has
allowed the atmosphere to destabilize quite a bit. Even the SPC
mesoscale analysis page is showing at least 1000 J/kg of MLCAPE
across our forecast area. Storms are already starting to pop up
this afternoon, especially northeast and southwest of the Phoenix
area. The HREF was doing a good job of picking up on this, with it
also showing outflow boundaries from this activity interacting
somewhere near the Phoenix area. We expect scattered coverage of
storms by late this afternoon/early evening, across much of south-
central Arizona, and also out west in southwest Arizona and
southeast California as that MCV pushes through. Due to the
scattered coverage of storms combined with slow storm motion, the
flooding risk will be even more elevated today, and thus a Flood
Watch is in effect forecast area-wide through 11 pm MST/PDT
tonight. In addition to flooding, any storm will be capable of
producing strong winds, small hail, and frequent lightning.

For Saturday, models are showing a slight increase in overall
instability, with some HREF members showing more widespread
convection compared to today. As with today, there are no good
indications of substantial larger scale disturbances, but there
very well could be another MCV or two to provide localized
enhanced ascent in addition to the typical terrain influences. If
today ends up producing an organized MCS resulting in a worked
over atmosphere, then Saturday should be less active for most
areas. WPC's Excessive Rainfall Outlook for both today and
Saturday has a fairly large slight risk area encompassing the
majority of Arizona, so we may end up needing a Flood Watch at
some point later today or on Saturday. Although forecast
confidence drops a bit going into Sunday, there looks to be very
little change in this potential active weather pattern as ample
moisture will remain in place. Day to day monsoon storm chances
are likely to persist into next week, but there is some ensemble
support for some slight drying early next week which likely
contributed to the decrease in NBM PoPs.

Temperatures today will again be quite warm with highs near 105
degrees across a good portion of the lower deserts, resulting in
localized Moderate HeatRisk. As monsoon storm activity likely
ramps up into the weekend, daytime highs should drop a bit with
NBM highs closer to 100-103 degrees.

&&

.AVIATION...Updated 1240Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Winds will favor diurnal tendencies through the rest of this
morning and into the early afternoon hours, mostly below 10 kts.
Shower/thunderstorm chances increase by late afternoon/early
evening (~40-50%) across the metro. Have added VCSH/VCTS to the
TAFs for later today. Any thunderstorms will be capable of gusty
erratic winds along with lightning, blowing dust and locally heavy
rainfall. Confidence in winds is low given the possibility for
multiple outflows from various directions. For now, have added a
NE outflow as this is currently the most favored solution. There
is a 20-30% chance outflow winds will exceed 30 kts in the Valley.
SCT- BKN clouds will mostly remain aoa 10 kft, dropping to around
8 kft with any convection.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will generally favor a SE to SW component at KIPL, while
winds mostly favor the S at KBLH. There will be about a 20-30%
chance for showers and thunderstorms this afternoon with the
primary impacts with any thunderstorms being gusty erratic winds
(30-40% chance >30 kts) along with blowing dust and lightning.
SCT-BKN clouds will mostly remain aoa 10 kft but may briefly drop
lower with any thunderstorms.

&&

.FIRE WEATHER...
Ample monsoonal moisture is expected to persist through at least
the first half of next week keeping the fire danger threat low.
This moist airmass will continue to yield elevated humidities
with afternoon minimum RH values mostly in a 30-35% range,
locally higher, and good overnight recovery. Chances for wetting
rains will continue for most areas almost daily, especially
through the weekend. Winds for the most part will remain light,
with the exception of thunderstorm outflows generating stronger
gusts.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flood Watch until 11 PM MST this evening for AZZ530>563.

CA...Flood Watch until 11 PM MST this evening for CAZ560>570.

&&

DISCUSSION...Feldkircher/Kuhlman
AVIATION...Smith
FIRE WEATHER...Kuhlman

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