Severe Thunderstorm Warning 268, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
923 AM MST Tue Aug 6 2024

.UPDATE...Current water vapor imagery shows an upper level low
centered over the border of Chihuahua and Sonora with a nose of
dry air extending from the Texas Panhandle through the White
Mountains and into western Pima County. This low will progress
northwestward today providing upper level support to storms this
afternoon and evening. The 12Z KTWC sounding measured 1.43 inches
of PWAT with dry air in the mid to upper levels. PWATS will
increase by about a tenth of an inch this afternoon ranging from
1.5" in Tucson to 1.75" in western Pima County and 1.1" along the
AZ/NM border.

The 06/12Z HREF and other CAMs initiate storms along a line from
Nogales to Tucson between 1 PM and 3 PM with storms then moving
westward into central and western Pima County and Pinal County.
Storms will be aided by 1000-1500 J/kg of MLCAPE along with steep
low-level to mid-level lapse rates. With the upper level moving
through 0-6 km shear will be elevated with the HREF showing values
between 30-40 kts. This will lead to strong updrafts and long-
lived storms with some supercells possible. Storms will be capable
of strong to severe wind gusts aided by 1500 J/kg of DCAPE and
the mid-level dry air currently shown on water vapor. Also can't
rule out some isolated severe hail as well. SPC has areas from
Tucson westward in a slight risk for severe weather. As storms
propagate westward blowing dust will also be an issue, so a
blowing dust advisory is in effect from 4 PM to 8 PM for areas
west and north of Tucson. Heavy rainfall will also be a threat
with these storms. HREF 3 hour probability matched mean QPF is
highlighting Santa Cruz County as well as southern Tohono O'odham
Nation with 50-70 percent chance for an inch or greater and 10
percent chance for three inches this afternoon and evening. WPC
also has areas from Tucson westward in a slight risk for excessive
rainfall. Please see the previous discussion for longer term
details.

&&

.PREV DISCUSSION... /issued 222 AM MST Tue Aug 6 2024/

.SYNOPSIS...A disturbance aloft will result in an active monsoon
pattern for Tuesday with numerous showers and thunderstorms,
especially from Tucson westward. Otherwise, expect scattered showers
and thunderstorms each day through this week, with potential for
heavy rainfall and strong wind gusts. Temperatures cool to near
normal levels Tuesday through Thursday, then warm up to above normal
levels Friday through the weekend.

&&

.DISCUSSION...Radar this morning was showing isolated showers and
t-storms moving west/southwest across Cochise, Pima and Santa
Cruz counties. The late evening round of storms produced localized
rainfall up to 0.75" and wind gusts up to 45 mph. Water vapor
imagery this morning showed an inverted trof across Chihuahua MX
moving slowly to the west. This feature will be the driver in our
weather today as it moves into Sonora MX, with the potential for
strong to severe thunderstorms and locally heavy rain, mainly from
Tucson west. 06/00z HREF showing much of the western half of
forecast area with 10% chance of wind gusts 58 mph or greater
between 3 pm and midnight as storms move to the west. Outflow
winds will kick up the dust, thus after coordinating with WFO
Phoenix a blowing dust advisory was issued from 4 pm to 8 pm for
areas west/northwest of Tucson. On the precip side, with PW values
in the 1.5" to 2" range west of Tucson, localized heavy rainers
are likely that will increase the threat flash flooding. With all
that said, SPC has outlined the western half of our area in a
marginal risk for severe thunderstorms due to wind and WPC has
pretty much the same area in a slight risk for flash flooding.
Will have to watch some of the washes across central Pima county
as they are running elevated this morning after recent rains.

Thunderstorm coverage on Wednesday is dependent on how worked
over the atmosphere ends up. With the inverted trof hanging around
southwest of the area heading into the weekend, daily chances of
storms continue Thursday into the weekend with day-to-day
variability on areal coverage of storms.

Near normal temperatures are expected today through Thursday,
then warmer temperatures return Friday through the weekend as
heights increase with perhaps a bit of drying.

&&

.AVIATION...Valid through 07/12Z.
FEW-SCT clouds at 10k-14k ft AGL thru 06/18Z, then SCT-BKN clouds at
6k-9K ft AGL and BKN-OVC clouds at 10k-14k ft AGL thru the end of
the forecast period. ISOLD -SHRA/-TSRA thru 06/18Z, then SCT-NMRS
SHRA/TSRA thru 07/06Z, before slowly diminishing thereafter. MVFR
conditions (locally IFR) expected near TSRA, with VSBY restrictions,
wind gusts to 45+ kts, heavy rain, low cloud heights and mountain
obscurations. Outside of thunderstorm wind gusts, wind speeds will
be less than 12 kts, favoring an ELY through SLY direction. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Scattered to numerous showers and thunderstorms
are expected today, with isolated to scattered mainly afternoon and
evening showers and thunderstorms Wednesday through the upcoming
weekend. 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...
Blowing Dust Advisory from 4 PM this afternoon to 8 PM MST this
evening for AZZ501-502-505.

&&

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