Flash Flood Warning 147, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
419 PM MST Sun Aug 14 2022

.UPDATE...0z Aviation Discussion...

&&

.SYNOPSIS...
Ample monsoonal moisture and favorable conditions for storms are
expected today with the best coverage of storms likely in La Paz,
Maricopa, northwest Pinal, and southern Gila counties where flood
watches are in effect for this afternoon and evening. Strong
winds, heavy rainfall, blowing dust, and lightning will also be
possible with any storm activity today. Rain chances decrease
slightly Monday/Tuesday, favoring high terrain areas. Better
moisture returns by the end of the week.

&&

.DISCUSSION...
Moisture levels have increased once again over south-central
Arizona, with more precipitable water in this morning's Phoenix
sounding than what was observed Friday morning. Values are right
around the max moving average for the day according to the SPC
sounding climo page. Surface dew points are also near 70 degrees
across our AZ areas and a little higher in southeast California.
So, it’s safe to say it’s moist out there. An MCV can also be seen
on satellite imagery around southern Gila county. This complex
looks like it will slowly move north and could continue to play a
role in triggering additional activity across the eastern parts
of south-central AZ this afternoon. In addition to this feature,
coverage of high terrain thunderstorms, both in So Cal and in
Arizona, is also expected to continue increasing this afternoon.
HREF suggests that outflows from these distant storms will
propagate into the lower deserts and there should be plenty of
instability for them to play with, with the SPC mesoscale analysis
page showing MLCAPE values in excess of 1000-2000 J/kg by this
afternoon across our forecast area (highest in southwest
Arizona). However, there is some uncertainty for the Phoenix
area, since the cloudiness associated with the aforementioned MCV
might be inhibiting the atmosphere from warming up enough. The
mesoscale analysis page even shows a good amount of convective
inhibition in the Phoenix metro lingering into the early evening.
Will the forcing from the outflows or MCV be enough regardless?
We shall see, but it does seem hi-res guidance, especially the
HRRR, is optimistic about scattered activity developing in the
Phoenix metro later today/tonight.

Due to extremely slow storm motion, an abundance of moisture, and
better storm coverage, a Flood Watch remains in effect for south-
central Arizona and La Paz county through 11 pm this evening. For
the rest of our CWA, coverage is expected to be less than the past
couple of days and that is why the Flood Watch was canceled for
today. However, that does not mean that flooding will not be a
risk, any thunderstorm that does develop will have the potential
to produce flash flooding in these areas today and tonight. In
addition to flooding, strong to severe winds, blowing dust,
frequent lightning strikes, small hail, and heavy rain will be
possible with any storm today. There is currently greater than a
30% chance of seeing wind speeds exceed 35 mph across most of our
forecast area this afternoon and evening, except for areas in or
around La Paz county who have greater than a 50% chance.

We start to dry out a bit again tomorrow as our flow starts to
turn back to the southwest. There will still be plenty of moisture
for high terrain thunderstorms, but will there be sufficient
energy to allow for additional convection to develop in the lower
deserts, especially after the activity we are expecting today and
tonight? HREF guidance suggests there may be just enough for
isolated activity. Regardless of location, any storm that develops
tomorrow will have the potential to produce frequent lightning,
strong to severe winds, blowing dust, small hail, and heavy rain.

A shift in the pattern will be more noticeable by Tuesday with
increasing subsidence seen across much of southern Arizona and
more dry air likely advecting in from the east from New Mexico.
Overall, it looks like Tuesday and Wednesday will only offer
limited storm chances across the lower deserts (10-20%) and 25-40%
over the eastern Arizona high terrain. Temperatures will also
warm up into the middle part of this week with more widespread
Moderate HeatRisk and highs around 105 degrees in the Phoenix area
to as warm as 107-109 degrees across the western deserts.

The expected lull in monsoon activity should be fairly brief as
ensembles show a return of deep moisture across the region at some
point later this week. This should coincide with a weakening
inverted trough forecast to track westward across northern Mexico
and the sub-tropical high getting reestablished across the Great
Basin. The NBM is rather bullish with PoPs by Friday into next
Saturday showing fairly widespread 30-50% chances across the lower
deserts, while lowering high temperatures into the 90s. However,
this is still several days out and forecast confidence is quite
low.

&&

.AVIATION...Updated 2320Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Currently tracking an outflow with gusty winds pushing south into
Metro Phoenix. Gusts up to 35kt are possible within the next hour
at SDL/PHX/IWA. Thereafter, widely scattered thunderstorms with
localized gusty winds will be with us through at least early
evening with 30-50% coverage anticipated. MVFR or even IFR
conditions cannot be ruled out on a short-term basis if you get
beneath TS. Quieter conditions are forecast later tonight as winds
go variable or easterly and light. Westerly component arrives by
early afternoon Monday, and isolated storms are again possible
later in the day. Will work on more detail RE: storm threats for
tomorrow in the next TAF package - once this evening's activity
has diminished.

Southeast California/Southwest Arizona including KIPL and KBLH:
IPL looks mostly quiet this evening with SSW winds backing to SE.
Storms to the mountains west of IPL have weakened and pushed
significant anvil debris overhead. BLH will see VCTS for the next
few hours. Prevailing winds at BLH will hold onto a southerly
component.

&&

.FIRE WEATHER...
Ample monsoonal moisture is expected to persist through the
majority of the coming week, keeping the fire danger threat low
for most locations. This moist airmass will continue to yield
elevated humidities with afternoon minimum RH values mostly in a
30-35% range, briefly dropping to 25-30% for Tuesday and
Wednesday. Chances for wetting rains will continue to be modest
today and Monday, but lower to less than 10% for most areas during
the middle part of the week. 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 AZZ533-534-537>563.

CA...None.
&&

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

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Special Weather Statement
National Weather Service Phoenix AZ
450 PM MST Sun Aug 14 2022

AZZ538-150030-
Tonopah Desert AZ-
450 PM MST Sun Aug 14 2022

...A strong thunderstorm will impact portions of Maricopa County
through 530 PM MST...

At 450 PM MST, Doppler radar was tracking a strong thunderstorm over
Palo Verde Nuclear Generation Station, or 8 miles southeast of
Tonopah, moving east at 5 mph.

HAZARD...Winds in excess of 40 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Palo Verde Nuclear Generation Station, Wintersburg and Hassayampa.

This includes AZ Interstate 10 between mile markers 97 and 109.

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 3331 11299 3349 11295 3349 11267 3322 11273
TIME...MOT...LOC 2350Z 281DEG 5KT 3339 11287

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

Iniguez

Special Weather Statement
National Weather Service Phoenix AZ
451 PM MST Sun Aug 14 2022

AZZ538-539-559-150030-
Sonoran Desert Natl Monument AZ-Tonopah Desert AZ-Gila Bend AZ-
451 PM MST Sun Aug 14 2022

...A strong thunderstorm will impact portions of Maricopa County
through 530 PM MST...

At 451 PM MST, Doppler radar was tracking a strong thunderstorm over
Gila Bend Auxiliary Field, or near Gila Bend, moving northeast at 15
mph.

HAZARD...Winds in excess of 40 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Gila Bend, Gila Bend Auxiliary Field, Bosque, Cotton Center, Sonoran
National Monument and Big Horn.

This includes the following highways...
AZ Interstate 8 between mile markers 99 and 141.
AZ Route 238 between mile markers 1 and 15.
AZ Route 85 between mile markers 1 and 16, and between mile markers
119 and 138.

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 3266 11274 3293 11305 3320 11264 3285 11230
TIME...MOT...LOC 2351Z 232DEG 11KT 3292 11274

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

Iniguez