Severe Thunderstorm Warning 137, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
255 PM MST Tue Jul 16 2024

.SYNOPSIS...Temperatures slightly above normal through the rest
of this week, with typical mid July moisture levels across the
region. This will result in the daily chances for showers and
thunderstorms. The main threats will continue to be strong gusty
outflow winds and heavy rainfall leading to localized flash
flooding.

&&

.DISCUSSION...We started this morning with some weak showers/
thunderstorms across Southeast Arizona, and we will likely finish
the day with more established stronger storms. The storm activity
we saw this morning was associated with a mid-level MCV that
tracked across southern Pima county and eventually moved into NW
Sonora Mexico. Typically in the wake of these types of features,
we see a subsidence field that hinders storm development. In this
case though, it is far enough away where it shouldn't have too
much impact on Southeast Arizona this afternoon.

There are three things that are around to help thunderstorm
activity/development today. The overall pattern is defined by a
mid-upper high centered over central New Mexico with the flow
around this feature resulting in a weak diffluent area across
Southeast Arizona. A trough moving into the Pacific Northwest will
force this high to align more into a NW-SE orientation, resulting
in an area of weak stretching deformation assisting with the
overall lift. The third thing of note today is a weak vort max in
northern Chihuahua Mexico that will continue to rotate around the
base of the upper high and push into the far SE corner of the
state this evening.

So, with this in mind...our thinking is that we will see
thunderstorms develop NE of Tucson this afternoon (which we are
already watching develop via radar). The latest 16/20Z HRRR has
these storms moving off the higher terrain into the Upper Gila
River valley between 4-6 pm. I would expect these storms to
produce a strong outflow as it moves off the terrain, potentially
impacting Safford. Otherwise, thunderstorms east and southeast of
Tucson will be pulse-type and/or delayed until the late afternoon
and evening as we start to see the impact of the approaching vort
max. I have confidence in the University of Arizona 16/12Z WRF-RR
run since it has been resolving the timing/location of convection
very well the past few days. This run delays the majority of the
activity well into the evening hours. Tucson will likely stay on
the northern periphery of the majority of storm activity, just
clipping the Tucson Metro Area late (between 8-10 pm MST) this
evening.

Drier air in the mid-levels of the storm residing in NM and will
push west and entrain into the thunderstorms along the Arizona/New
Mexico border. The 16/12Z HREF is suggesting a 50-70 percent
likelihood of wind gusts in excess of 30+ kts from storms east of
Tucson today. It should be noted that 16/00Z HREF run had a 10
percent chance of wind gusts in excess of 50 kts but has backed
off on this run. The 16/12Z HREF is also pinpointing the heaviest
rainfall to occur S and SE of Tucson in Cochise and Santa Cruz
counties this afternoon/evening with a 10-30 percent chance of
3-hr rainfall amounts in excess of 1 inch, and even a 10 percent
chance of rainfall in excess of 3 inches along the International
Border.

In general, the main threat from storms today will be strong and
gusty thunderstorm outflows, but heavy rainfall is also in the
mix...especially S and SE of Tucson in Cochise and Santa Cruz
county where there is a better mix of moisture and will be
impacted by the weak vort max later this evening.

Otherwise, we will see a continued chance of mainly afternoon and
evening thunderstorms persist into early next week. The upper high
center will slowly drift into NW Arizona by late this week, then
near southern Nevada by the weekend. This puts us in into a more
favorable pattern for strong storms as the flow will move off the
Mogollon Rim/higher terrain into SE AZ. However, resolving which
day that will be more active at this juncture is difficult.

&&

.AVIATION...Valid through 18/00Z.
SCT-BKN clouds at 8k-12k ft AGL thru 17/05Z and again aft 17/18Z,
with diminishing cloud cover between 17/05Z and 17/18Z. SCT
TSRA/SHRA thru 17/05Z, mainly east through south of KTUS and in the
White Mountains. SCT TSRA/SHRA developing again aft 17/19Z. MVFR
conditions in TSRA, with mountain obscurations, vsby reductions and
wind gusts to 40+ knots. Outside of TSRA, SFC wind at most locations
12 knots or less favoring a WLY/NWLY direction during the afternoon
and early evening hours and variable in direction at other times.
The exception will be in the upper Gila River valley near KSAD where
WLY/NWLY SFC wind will be 16-22 kts with gusts to 32 kts thru
17/04Z. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Deeper moisture remains across southeast Arizona,
with typical mid July moisture levels expected through at least the
upcoming weekend. This will result in the daily cycle of mainly
afternoon and evening showers and thunderstorms. The main threats
will be strong, gusty and erratic outflow winds and heavy rainfall
leading to localized flash flooding. Minimum relative humidity
values will be 20-30 percent in most lower elevation locations and
25-40 percent in mountain areas. Away from thunderstorms, 20-foot
winds will generally be 15 mph or less, with afternoon/early evening
gusts to 20-25 mph and light winds overnight. Wind direction during
the afternoon will primarily be west to northwest into the weekend.
The exception will be in the upper Gila River valley around Safford,
where afternoon/early evening winds will be west-northwest around 20
mph and gusts to 30-35 mph through this evening.

&&

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

&&

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Preliminary Local Storm Report
National Weather Service Tucson AZ
210 PM MST Tue Jul 16 2024

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

0502 PM     Flash Flood      8 ENE Sierra Vista      31.60N 110.19W
07/15/2024                   Cochise            AZ   Law Enforcement

            DELAYED REPORT Photo on Cochise County
            Sheriff Office Facebook page showing
            flooding over Monson Rd leading to road
            closures. No exact timing on when the road
            was closed. Road currently open to local
            traffic only during cleanup. Time is
            estimated based on the radars heaviest
            rainfall.

&&

JVT