Flash Flood in Arizona, August 8 to 9, 2024

Area Forecast Discussion
National Weather Service Tucson AZ
147 PM MST Thu Aug 8 2024

.SYNOPSIS...Scattered showers and thunderstorms each day into this
weekend with the exception of Saturday which could see reduced
coverage. Storms will have the potential for heavy rainfall and
strong wind gusts. Temperatures slightly below normal today then
warm up to above normal levels Friday through the weekend into
early next week.

&&

.DISCUSSION...Storms are beginning to pop up over the higher
terrain as of 1:30 PM this afternoon over the Sky Islands. There
is still some debris clouds mainly over Western Pima County,
Tohono O'odham Nation, and Northeastern Graham County. The
activity should remain in the higher elevations over the next
couple of hours before making their way into the valley floors
later this afternoon and evening. The thunderstorm ingredients are
either in place or beginning to shape up with MLCAPE being in the
1000-1500 J/kg range over most of Southeast Arizona, where the
only exceptions are where the remnants of the debris clouds are
located with some CIN being there due to lack of surface heating.
The PWs are ranging from 1.00"-1.75" with the higher values areas
Tucson westward. Areas with the best shear are areas north of the
forecast area, however there is some weak directional shear with
the surface being from the NW and the overall upper flow from the
SE, so there could be some potential for sustained updrafts. Since
we are still in that moister environment, DCAPE is in the 700-900
J/kg range, decreasing the overall severe wind threat, but is
still possible. Aiding in longer lived updrafts is the semi-
favorable placement of the upper level low that is currently
located over the Gulf of California making some upper level
diffluence available as well. Interestingly, the RAP model is
showing some areas of 1-3 in the Microburst Composite, so that is
something of note that stronger storms are possible today. Similar
to yesterday there is very light steering flow of 5-10 kts so
thunderstorms will be slow moving with possible accumulations
between 1"-2" and can be higher in localized areas. The main
threats with thunderstorms this afternoon and evening are heavy
rainfall leading to possible flash flooding, some gusty winds
(30-40 mph), and frequent lightning. Overnight some CAMs are still
hanging onto some thunderstorm activity through about 2 AM, so
that is something to keep in mind tonight.

Looking ahead to tomorrow, the overall activity is very much
dependent on if/how long thunderstorm activity sticks around in
the overnight hours to determine how active it is on Friday
afternoon and evening. Conditions are still favorable for
thunderstorm activity with moisture sticking around for much of
the forecast area minus areas east of Tucson, daytime heating,
and lift still available. The HREF CAMs are highlighting
southeastern Pinal, Pima, and Santa Cruz counties but not as much
in coverage as today. The weekend continues to look to decrease
in activity slightly with each day as the moisture begins to cycle
and limit much of the coverage to areas mainly west of Tucson.

After this weekend, there is currently no hints at any extra
dynamics or moisture surge in the longer range models to increase
confidence on any specific higher impact monsoon days as of now.
Overall high temperatures are slightly above normal (3-6 degrees)
though next weekend. Stay tuned to forecast as it changes.

&&

.AVIATION...Valid through 10/00Z.
SCT-BKN clouds at 6k-9k ft AGL and BKN-OVC clouds AOA 15k ft AGL
thru this evening then gradual clearing overnight into the
morning. SCT SHRA/TSRA thru 09/06Z, slowly diminishing
thereafter with possible ISOLD SHRA/TSRA thru 09/09Z. MVFR
conditions expected near TSRA, with VSBY restrictions, wind gusts
to 40+ kts, heavy rain and mountain obscurations. Outside of
thunderstorm wind gusts, wind speeds will be less than 12 kts,
favoring an SWLY through NWLY direction in the afternoon and early
evening hours and variable in direction at other times. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Isolated to scattered mainly afternoon and evening
showers and thunderstorms are expected through the upcoming
weekend with a possible down day Saturday. There is a chance for
some overnight activity tonight. Min RH values will be in the
25-40 percent range in the valleys through Thursday (and higher in
the mountains), decreasing to 15-30 percent Friday through the
weekend for the upper Gila Valley and Sulfur Springs Valley.
Outside of 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.
&&

Tetrault

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