Flash Flood Warning 107, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
541 AM MST Fri Aug 12 2022

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
Today and through the weekend will bring increased chances for
monsoon storms, particularly across higher terrain areas. Storm
activity will tend to favor the afternoon and evening hours with
strong winds, heavy rainfall, and localized flooding all possible.
After near normal temperatures today, slightly cooler temperatures
are expected over the weekend with increased cloud cover. Chances
for showers and thunderstorms will persist into early next week,
but likely to a lesser degree compared to over the weekend.

&&

.DISCUSSION...
After fairly isolated storms on Thursday, the atmosphere has
recovered with higher instability now encompassing the majority
of the area. Current objective analysis shows ample moisture
across the entire region, but overall little convection ongoing
early this morning. What current shower activity is there is
mainly associated with two separate MCVs located just south of
Pima County and another across far southeast Arizona, both of
which are very slowly drifting to the west northwest.

Assuming the MCV across southeast Arizona doesn't spawn much more
shower or thunderstorm activity this morning, cloud cover to start
out the day should be somewhat minimal aiding in good insolation
and destabilization by this afternoon. Forecast soundings later
today across the lower deserts still show measurable CIN, but
expected insolation should be sufficient to get fairly widespread
high terrain storms firing by mid afternoon. General consensus
among hi-res models is for fairly widespread afternoon convection
along the Rim through Gila County and some scattered activity over
elevated terrain areas like the Kofa's and Table Top area. Low
level mixing ratios will be fairly good at 10-12 g/kg, but not
indicating excessive moisture to where DCAPEs are too low for
decent storm outflow production. The CIN over lower elevation
areas is likely to initially inhibit further development along
weaker outflows, but any organized deeper outflows should be
enough to erode the CIN for additional storm development.

Unfortunately, the 00Z HREF members show very little agreement
for lower desert storm development this evening with the HRRR
favoring the Phoenix area, NSSL over southern Maricopa Co., and
the ARW across the Lower Colorado River Valley. However, NBM PoPs
across the area today are notably higher than yesterday with
20-30% across the western deserts, 35-45% in the Phoenix area, and
50-60% over the high terrain north and east of Phoenix. Models do
not indicate any organized ascent areas from larger scale
disturbances, but the current MCVs may persist long enough to
enhance convection mainly south of Phoenix. Given the expected
environmental parameters today, isolated strong winds, patchy
blowing dust, heavy rainfall, and localized flooding will all be
possible. Will hold off on any Flood Watches for now due to the
lack of a good focusing mechanism for organized storms and HREF
disagreement, but there very well could be a few storms that
produce heavy rainfall amounts capable of producing localized
flooding.

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...None.
CA...None.
&&

DISCUSSION...Kuhlman
AVIATION...Smith
FIRE WEATHER...Kuhlman

Special Weather Statement
National Weather Service Phoenix AZ
936 AM MST Fri Aug 12 2022

AZZ532-CAZ565-121715-
Yuma AZ-Imperial County Southeast CA-
936 AM MST Fri Aug 12 2022

...A strong thunderstorm will impact portions of west central Yuma
and southeastern Imperial Counties through 1015 AM MST/1015 AM
PDT/...

At 935 AM MST/935 AM PDT/, Doppler radar was tracking a strong
thunderstorm over Yuma, moving northwest at 15 mph.

HAZARD...Winds in excess of 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Yuma, Winterhaven, Araby, Algodones Dunes and Andrade.

This includes the following highways...
AZ Interstate 8 between mile markers 1 and 8.
AZ Route 95 between mile markers 29 and 30.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 3264 11477 3272 11472 3271 11475 3270 11493
      3272 11498 3295 11482 3273 11447 3258 11459
TIME...MOT...LOC 1635Z 120DEG 14KT 3270 11463

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

Feldkircher

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