Severe Thunderstorm Warning 166, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
442 PM MST Sun Aug 21 2022

.UPDATE...Updated 00z Aviation Discussion...

&&

.SYNOPSIS...
Another chance for storms mainly across Maricopa, northwest Pinal,
and La Paz counties between 3 pm and 10 pm today. Isolated severe
winds will be possible. Storm chances trend lower Monday before
increasing again by Wednesday. Another downtrend in storm chances
by the end of next week. Temperatures will follow a similar trend
but with higher temperatures on days with lower storm chances.
Overall, temperatures are anticipated to be below normal.

&&

.DISCUSSION...
Phoenix ended up breaking its daily precipitable water record
once again today, with 1.95 inches observed in this mornings
sounding. In addition, surface dew points are in the upper 60s to
lower 70s across our deserts. Although we have seen some drying
over the past 24 hours, it remains evident that we still have
plenty of moisture in the atmosphere today. In terms of the
synoptic pattern, the mid-level flow is more out of the north-
northeast today and that disturbance that brought us a substantial
amount of rainfall over the past few days is also going to be
forced eastward over the next 24 hours. For the remainder of the
day, hi-res guidance continues to suggest that convection will
continue developing along the rim this afternoon, with activity
then propagating southwestward into south-central Arizona and
parts of southwest Arizona and the Colorado River Valley. Outflows
from this activity are most likely to move into the lower deserts
after 3 pm. There should be plenty of instability to support
additional storms as these outflows push through, with the
mesoscale analysis page forecasting greater than 2000 j/kg of
mlcape this afternoon. The best chances for storms will be across
south-central Arizona and in La Paz county in southwest Arizona.
Slightly drier air will increase the damaging wind risk and lower
the flood risk slightly compared to yesterday. The probability of
getting greater than 35 mph winds is around 70% in the Phoenix
area, greater than 50% across northwest Pinal and the rest of
Maricopa county, and greater than 30% across southwest Arizona. In
addition, isolated severe winds (greater than 58 mph) will be
possible, and due to this there is a marginal risk of severe
storms mainly across Maricopa (including the Phoenix metro),
northwest Pinal, and La Paz counties. Due to the potential for
strong winds, blowing dust will also be a risk in dust prone
areas. With slightly faster storm motion and slightly less
moisture in the atmosphere, the chance of getting more than 3” of
rainfall in 3 hours is less than 10% (for reference, the chance
was 10-30% the past few days). However, even though the Flood
Watch isn’t in effect today, localized flooding will still be
possible with any storm. Further west in southeast California,
regardless of moisture, this pattern isn’t necessarily the most
favorable for storms out there. The best chances will be across
JTNP, where an isolated storm can’t be ruled out this afternoon.

High pressure to our west starts to move eastward, drying us out
a little more and increasing 850 mb temps approximately 5 degrees
tomorrow. Our flow will remain out of the north-northeast, and we
can expect a similar story tomorrow, but with less moisture and
more limiting temperatures aloft. HREF is showing less convection
firing off along the rim by the early afternoon. Activity and
associated outflows will once again try to propagate towards the
lower deserts but with less support, storms look like they will
struggle to survive. It’s possible that a few isolated storms
develop, but coverage looks to be substantially less than what
we’ve seen the past few days. The chance for getting greater than
35 mph wind speeds lowers to 10-30% across south-central Arizona
and generally around 10% or less across the western deserts. The
best time frame for outflows and isolated convection would be
between 3 and 10 pm, with the best coverage across the high
terrain north and east of Phoenix.

The flow turns more easterly Tuesday into Wednesday as the high
starts to shift towards the 4 corners. 850 mb temps are warmest
with the center of the high closest on Tuesday. PWs drop more
across our forecast area as well on Tuesday, and only isolated
storms look possible, favoring south-central Arizona. Wednesday
currently looks like it will be another good day for lower desert
storms, even as far west as southeast California. Moisture
increases once again and our flow is a lot more favorable.
Definitely something we will continue to keep an eye on. Low
confidence on the forecast beyond Wednesday, but it does appear
that Thursday could be active again and then we start to slowly
dry out and warm up again towards the weekend as our flow turns
more westerly.

Below normal temps will continue for at least the next week with
minor heatrisk across south-central and southwest Arizona and
minor to moderate heatrisk across southeast California.

&&

.AVIATION...Updated 2335Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Watching several clusters of strong thunderstorms across Yavapai
County moving southward towards the valley. Confidence of any
thunderstorm directly affecting the terminals remains low and thus
VCTS continues to be reflected in the latest TAF package issuance.
However, there is higher confidence of outflow winds from the
north from these thunderstorms affecting the terminals with timing
expected to be between 01z and 03z for impacts. There continues to
be a greater than 50% probability of winds exceeding 30 knots and
about a 5% probability of winds exceeding 50 knots with these
outflows. As these storms continue to inch closer to the area,
cloud cover coverage will increase to SKN-BKN with bases aoa 5-7
kft. Conditions should improve by late evening with light and
variable winds likely into the overnight with an easterly switch
early Monday morning. A westerly shift is anticipated by late
morning into the early afternoon. Thunderstorm potential and
associated outflow impacts appears lower for Monday afternoon/
evening, with a 10-30% probability of winds exceeding 30 knots.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns expected through the period.
Prevailing wind direction will be from the southeast at KIPL and
from the south at KBLH with speeds generally around 10 kts. Cloud
coverage will generally be FEW to locally SCT with bases aoa 15
kft.

&&

.FIRE WEATHER...
Very elevated moisture with min RH values >30-50% today with
excellent overnight recoveries >65-80% across the region. Storm
chances will be greatest across the rim north and east of the
Phoenix metro today, however, isolated to scattered storms will be
possible in the lower deserts of south-central & southwest AZ as
this activity propagates southward. Winds on average will be
light, with the exception of any thunderstorm or associated
outflows generating stronger gusts. Well below normal max Ts
today. Drier and slightly warmer conditions with a downtick in
storm activity is likely tomorrow before another uptick by
midweek. Much drier conditions are then forecast by next weekend
with min RH values in the lower deserts generally less than 30%.

&&

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

DISCUSSION...Feldkircher
AVIATION...Lojero
FIRE WEATHER...Feldkircher

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Special Weather Statement
National Weather Service Phoenix AZ
800 PM MST Sun Aug 21 2022

AZZ538-539-559-220330-
Sonoran Desert Natl Monument AZ-Tonopah Desert AZ-Gila Bend AZ-
800 PM MST Sun Aug 21 2022

...A strong thunderstorm will impact portions of Maricopa County
through 830 PM MST...

At 800 PM MST, Doppler radar was tracking a strong thunderstorm near
Bosque, or 8 miles east of Gila Bend, moving south at 15 mph.

HAZARD...Wind gusts up to 50 mph.

SOURCE...Radar indicated.

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

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

This includes the following highways...
AZ Interstate 8 between mile markers 114 and 139.
AZ Route 238 between mile markers 1 and 16.
AZ Route 85 between mile markers 1 and 4, and between mile markers
119 and 126.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3302 11270 3301 11244 3279 11230 3280 11270
      3295 11277
TIME...MOT...LOC 0300Z 344DEG 13KT 3292 11255

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH

INS

Special Weather Statement
National Weather Service Phoenix AZ
815 PM MST Sun Aug 21 2022

AZZ533-534-538-220400-
Aguila Valley AZ-Tonopah Desert AZ-Central La Paz AZ-
815 PM MST Sun Aug 21 2022

...A strong thunderstorm will impact portions of east central La Paz
and Maricopa Counties through 900 PM MST...

At 815 PM MST, Doppler radar was tracking a strong thunderstorm 8
miles east of Wenden, or 31 miles south of Alamo Lake, moving south
at 15 mph.

HAZARD...Wind gusts up to 50 mph.

SOURCE...Radar indicated.

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

Locations impacted include...
Wenden, Gladden and Salome.

This includes US Highway 60 between mile markers 60 and 79.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3395 11352 3394 11327 3371 11316 3364 11339
      3366 11362
TIME...MOT...LOC 0315Z 356DEG 11KT 3383 11341

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH

INS