Severe Thunderstorm Warning 220, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
203 PM MST Sat Jul 27 2024

.SYNOPSIS...

Daily chances for showers and thunderstorms this weekend and into
next week with the main threats being heavy rainfall with isolated
strong wind gusts. Localized flash flooding will be possible.

&&

.DISCUSSION...

In the upper levels, a ridge axis was placed from southeastern
Arizona into southern Colorado, while a jet streak was crossing
south-central California through Utah. GOES-West water vapor
imagery showed evidence of favorable convective placement this
afternoon in southern and eastern areas of southeastern Arizona,
with drier mid-level air and less synoptic support further
northwest. This keeps Tucson on the edge of the better convective
probabilities, with chances increasing south towards Nogales and
east towards Safford, Douglas, and the New Mexico border.

As of time of discussion, convection has been well under way
across areas of Santa Cruz, Cochise, Graham, and Greenlee
counties. Moderate instability, slow storm motions, and decently
moist mid- levels will allow for the threat of heavy rainfall
capable of producing flash flooding, especially as these slow
moving thunderstorms sit over locations vulnerable to excessive
rain. Though not the primary threat, enough mid-level dry air has
moved in to allow for an isolated strong to severe wind gust under
any thunderstorm.

Coverage this evening will rapidly diminish with sunset. A few
high-res models such as the HRRR and UofA WRF produce a batch of
early Sunday morning showers, which seems reasonable as some
instability aloft should remain and the fact hat
showers/thunderstorms were observed early this morning.

Tomorrow, the upper high shifts east a bit and mean flow over
southeastern Arizona becomes southerly. This will bring another
day of likely active monsoon weather, this time better oriented to
potentially bring thunderstorms into the Tucson metro. Forecast
chances are fairly widespread, maximized from Santa Cruz through
Cochise counties where initiation should happen first. Heavy
rainfall and isolated strong wind gusts remain the primary
threats.

Looking through next week, the upper level high should remain
centered east of the region, keeping southerly flow over
southeastern Arizona and daily chances for some sort of coverage
of thunderstorms. With the above normal height anomalies, daily
high temperatures should generally remain above normal.

&&

.AVIATION...

Isolated to scattered thunderstorms through 28/02Z near KOLS-KDUG
and up north through KSAD, with a slight chance of one near KTUS.
Very heavy rainfall and isolated gusty outflow winds to 45 kts
near any thunderstorm today. Otherwise winds generally under 12kts
this afternoon and becoming light tonight. Chances for
thunderstorms expected again Sunday afternoon.

&&

.FIRE WEATHER...

Scattered afternoon and evening showers and
thunderstorms with day to day variability on which areas will see
the best chance of rainfall. Each day has the threat of heavy
rain, localized flash flooding and strong gusty winds. Minimum
relative humidities will be 20 to 30 percent in most lower
elevation locations and 25 to 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. As high pressure builds mid-week, high
temperatures should rise a bit and minimum relative humidities
should fall by a few percentage points.

&&

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

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Preliminary Local Storm Report
National Weather Service Tucson AZ
216 PM MST Sat Jul 27 2024

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

0213 PM     Rain             10 SE Sierra Vista      31.48N 110.19W
07/27/2024  M2.57 Inch       Cochise            AZ   Trained Spotter

            Trained spotter observed 2.57 inches in 50
            minutes. Rain letting up at time of report.

&&

AJE