Severe Thunderstorm Warning 351, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
907 AM MST Wed Aug 21 2024

.SYNOPSIS...An active monsoon period through Thursday across
much of southeast Arizona. Thereafter, some drying Friday into the
weekend will result in isolated thunderstorms mainly east of Tucson.
Thunderstorms each day will be accompanied by the typical monsoon
threats of strong wind gusts, localized heavy rainfall and flash
flooding, and blowing dust. High temperatures near to slightly above
normal through the forecast period.

&&

.UPDATE...

This morning we've got an MCV moving into our area, sticking
mainly to the south and west of Tucson, from Mexico that is
bringing storms and showers along with it. The complex is moving
to the northwest and will continue to bring showers for much of
the morning. Outside of the MCV, to the north and east of Tucson
skies are mostly sunny this morning. This afternoon, thunderstorm
activity is still expected and will be stronger than this
morning. With increasing PWAT's of 1-1.8 inches across the area
and substantial DCAPE of 1000-2000 J/kg, storms that develop will
be capable of producing strong to severe winds and locally heavy
rainfall that can lead to flash flooding. Convection looks to
begin around 1 to 2 PM MST focused to the south and east of Tucson
becoming more widespread across southern AZ as the afternoon
progresses. Chance for storms and showers in Tucson will be around
4 to 7 PM. Heat will not be as much of a concern as it was
yesterday with high temperatures decreased slightly. We are in
Minor HeatRisk today, meaning that only those who are extremely
sensitive to heat and those who do not have a way to stay
hydrated or properly cooled will be impacted.

&&

.PREV DISCUSSION... /issued 227 AM MST Wed Aug 21 2024/

.DISCUSSION...Mostly clear skies this morning east of Tucson with
partly cloudy skies west of Tucson. Radar is mostly quiet at this
time with the exception of a lone shower or two over the T.O. Nation
and SE Pinal County. The ingredients are coming together nicely for
an active monsoon day today across much of southeast Arizona. PWAT
values are trending a bit higher for much of the forecast area (1.4
to 1.8 inches from Tucson westward), though a bit drier out east
near the NM border still hanging around 1 inch. We'll be under south-
southeast flow aloft between high pressure over New Mexico and a
trough across the west coast. While there are no discernible large
scale features embedded in this flow on water vapor imagery, it's
certainly likely smaller mesoscale features could help enhance lift
today. Given that we'll be starting out with considerable solar
insolation, that will result in destabilization with MLCAPE values
per the HREF increasing to around 1000 to 2000 J/KG for much of the
area later. Focus area for most widespread convection this afternoon
into evening will generally be west of a Douglas-Safford line and
east of a line from Sells-Eloy. Expect a hybrid of both severe
threat due to strong winds (blowing dust as well W/NW of Tucson) and
a flash flood threat as well. The flash flood threat will be focused
on Pima and Santa Cruz Counties where the deepest moisture resides.
We did consider a Flash Flood Watch but confidence is low in large
scale clustering to produce widespread flash flooding with storm
motions also around 15 mph. Will continue to message localized flash
flooding. The Weather Prediction Center (WPC) and Storm Prediction
Center (SPC) have placed our area under a slight risk for excessive
rainfall and a marginal risk for severe thunderstorms, respectively.

Still plenty of moisture to work with for Thursday for scattered
showers and thunderstorms for most of the forecast area. A more
noticeable drying trend starts on Friday as the flow aloft becomes
more southwesterly which allows for additional drying aloft. Still
isolated to scattered showers and thunderstorms from Tucson eastward
Friday, then just isolated showers and thunderstorms south and east
of Tucson this weekend. By early to mid next week, the flow pattern
will become more southerly to southeasterly again allowing an
increase in thunderstorm coverage back to seasonable levels for
late August.

Temperatures will be near to slightly above normal through the
forecast period.

&&

.AVIATION...Valid through 22/12Z.
SCT clouds at 6k-9k ft AGL this morning. Aft 21/19Z, SCT-BKN clouds
at 6k-9k ft AGL and SCT SHRA/TSRA for much of the forecast area thru
22/034, then diminishing thru the end of the forecast period. MVFR
conditions near TSRA, with VSBY restrictions, wind gusts to 45+ kts,
heavy rain and mountain obscurations. Outside of thunderstorm wind
gusts, wind speeds will be 12 kts or less, favoring a SELY direction
this morning, then SWLY thru NWLY direction this afternoon into
evening. SFC wind variable in direction at other times. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Mainly afternoon and evening showers and
thunderstorms can be expected across southeast Arizona through
Thursday, with a drying trend Friday through the weekend resulting
in a reduction in thunderstorm activity. High temperatures will be
near to slightly above normal through the forecast period. Min RH
values will be in the 25-35 percent range in most valleys locations
through Thursday, lowering to around 18-28 percent Friday through
the weekend as drier air overspreads the area. Outside of any
thunderstorm outflow winds, 20-foot winds will generally be 15 mph
or less, with afternoon/early evening gusts to 20-25 mph and light
winds overnight.

&&

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
None.
&&

Public...Malarkey
Aviation...Aviation Forecaster
Fire Weather....Fire Weather Forecaster

Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson

Preliminary Local Storm Report
National Weather Service Tucson AZ
1212 PM MST Wed Aug 21 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1020 AM     Flash Flood      1 SSE Nogales           31.36N 110.93W
08/21/2024                   Santa Cruz         AZ   Public

            Video shared of flooding on roadway next to
            Nogales Wash. Time estimated based on
            internal webcam footage.

&&

Preliminary Local Storm Report
National Weather Service Tucson AZ
1221 PM MST Wed Aug 21 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1221 PM     Hail             8 WNW Tucson            32.22N 111.02W
08/21/2024  M1.00 Inch       Pima               AZ   Trained Spotter

            Report from trained spotter of accumulating
            1 inch hail.

&&

Preliminary Local Storm Report
National Weather Service Tucson AZ
1225 PM MST Wed Aug 21 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1223 PM     Hail             8 WNW Tucson            32.24N 111.02W
08/21/2024  M1.25 Inch       Pima               AZ   Trained Spotter

            Trained spotter reported 1.25 inch
            accumulating hail.

&&

Preliminary Local Storm Report
National Weather Service Tucson AZ
1242 PM MST Wed Aug 21 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1030 AM     Flash Flood      1 SSE Nogales           31.35N 110.93W
08/21/2024                   Santa Cruz         AZ   Public

            Video showing water over bridge. Time
            estimated by radar and internal webcam
            footage.

&&