Severe Thunderstorm Warning 279, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
104 PM MST Wed Aug 7 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 cool to near normal levels today
and Thursday, then warm up to above normal levels Friday through
the weekend.

&&

.DISCUSSION...Temperatures are 4-10 degrees less than this time
yesterday thanks to the cloud cover in place over some of the CWA.
The upper level low is now situated over western Sonora and the
Gulf of California. Storms have already begun to form over the
Huachucas, Mt Graham, and the White Mountains. Expect this
activity to continue with storms mainly confined to the higher
terrain from Tucson eastward over the next couple of hours with
storms then moving into the lower deserts. Areas with lingering
mid-level clouds such as Tucson could have a late start or
struggle some with storm formation. However ingredients for storms
are still in place with MLCAPE of 1000-2000 J/kg, PWAT ranging
from 1.25"-1.75", and moderate 0-6 km shear of 15-20 kts. Storms
will be capable of strong winds and heavy rainfall with heavy
rainfall expected to be the bigger threat. DCAPE values are only
around 700 J/kg. HREF rainfall probabilities are highlighting
areas just south of the Tucson metro, Santa Cruz County, and
western Cochise County for the greatest chance of heavy rainfall.
Three hour probability matched mean for greater than 1" of QPF is
70 percent for these areas this afternoon and evening. Isolated
amounts of 2" will also be possible. Storms will also be slower
moving with steering flow around 5-10 knots, which will aid the
heavy rain threat.

CAMs aren't showing much if any nocturnal showers or thunderstorms
which should leave Thursday with more insolation than today.
Moisture and instability will be similar to today, so expect
scattered thunderstorms mainly from central Pima County eastward
during the afternoon and evening. The HREF favors eastern Pima
County, Santa Cruz County, and Cochise County to be the most
active. The upper level low will sit over the northern portion of
the Gulf of California, which is a little further east than
previous model runs and could slightly enhance the 500 mb flow.
Storms will be capable of strong winds and heavy rainfall leading
to localized flash flooding. The HREF is highlighting Cochise
County to see the best chances for heavy rainfall with the 3 hour
QPF PMM showing a 10 percent chance for 3 inches of rain and 70
percent for 1".

Friday eastern areas begin to lose moisture, which could lead to
reduced storm coverage especially if the atmosphere is worked over
from Thursday's storms. But areas from Benson westward could still
see storms. Temperatures also begin to increase as high pressure
becomes centered over New Mexico. Saturday the upper level low
moves west over Baja California and models further dry out
southeast Arizona, which will lead to further reduced storm
coverage. High temperatures will also increase to 4-7 degrees
above normal.

Sunday into early next week moisture returns to normal levels with
daily afternoon and evening thunderstorms expected. Mid-week a
possible pattern change looks to take place with a trough setting
up on the West Coast. Ensembles still differ with how far south
the trough extends which will determine whether southeast Arizona
switches from southeasterly flow to drier southwesterly flow.

&&

.AVIATION...Valid through 09/00Z.
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 08/03Z, slowly diminishing
thereafter. 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. Min RH values will be
in the 25-40 percent range in the valleys through Thursday (and
higher in the mountains), decreasing to 20-30 percent Friday
through the weekend. 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.
&&

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