Severe Thunderstorm Warning 91, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
902 AM MST Fri Aug 18 2023

.SYNOPSIS...Scattered showers and thunderstorms are expected
again this afternoon and evening with cooler temperatures.
Moisture being pushed toward Arizona from Hurricane Hilary is
expected to enhance the rainfall of showers and thunderstorms
across areas south and west of Tucson Saturday afternoon through
Saturday night. Otherwise, cooler temperatures and scattered
showers and thunderstorms are expected late this weekend into next
week.

&&

.DISCUSSION...Currently some weak showers and associated cloud
cover to the south of Tucson. This will likely last another hour
then skies will begin to clear some. Skies are already clear east
of Tucson. Today looks to be a fairly active day. The 18/12Z HREF
and other CAM models show convection starting this afternoon
mainly east of Tucson at first. Storms then progress
west/northwest likely along outflows and move through Tucson late
this afternoon or early evening then continue into central and
western Pima County. The main threats with these storms will be
strong to severe outflow winds as well as heavy rainfall and
localized flash flooding. Storms will also be aided by a weak
impulse moving in from the east. The HREF shows 70-90 percent
neighborhood probabilities of winds greater than 30 kts for most
of southeast Arizona and a 10 percent neighborhood probability for
winds greater than 50 kts in Pinal County and central/western
Pima County. Blowing dust will likely be an issue this evening in
Pinal County and central Pima County. High temperatures will be
right around normal. Please see the previous discussion for longer
term details.

&&

.AVIATION...valid through 19/18z.
ISOLD -SHRA with bases 8-12k ft AGL this morning. Areal coverage
incrg aft 18/19z to SCT -SHRA/-TSRA and contg thru 19/07z before
diminishing toward end of valid pd. Typical diurnal trends for SFC
winds 8-15 kts. Erratic wind gusts of 35-45 kts near any TSRA.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Scattered showers and thunderstorms are expected
again today with likely more widespread activity and with a few
severe storms possible. Then Saturday afternoon through Saturday
night heavy rainfall producing showers and thunderstorms are
possible south and west of Tucson thanks to moisture from tropical
storm Hilary. Gusty southeasterly winds are expected Sunday
afternoon, strongest in the Gila valley, however minimum humidity
levels will range from the mid 20s in the Gila Valley to 40+ Tucson
westward. After that, we will have the typical daily rounds of
scattered showers and thunderstorms with temperatures and humidity
level running closer to normal, which hasn't been the norm lately.

&&

.PREV DISCUSSION... /issued 330 AM MST Fri Aug 18 2023/
The scattered showers/isolated thunderstorms that were across the
area before midnight have pushed north of the forecast area. A
few light showers still possible this morning as radar is showing
a few south of the Intl border. The special Tucson 06z sounding
had a PW value up near 1.70" although that value was contaminated
a bit due to the thunderstorms that were around at release time.
The 12z sounding should give a better idea where the Tucson PW is
at.

Although debris clouds will slow down heating an hour or two
today, the combination of a moist atmosphere and a disturbance
aloft moving in from east later today will bring scattered showers
and thunderstorms. A few of the storms will be strong to severe
with locally heavy rain. Blowing dust may be an issue this evening
W-NW of Tucson.

Still on track with additional moisture pushing across the area
this weekend associated with Hurricane Hilary. The 3 am advisory
had Hilary located 400 miles S of Cabo San Lucas MX as a cat 4
hrcn. Little has changed with track of Hilary west of Baja Pen and
weakening as it moves into cooler waters. Little has changed from
previous forecast for our area with areas south and west of
Tucson seeing the best chances for heavy rain that could produce
flash flooding. No changes were made to the flood watch area.
Areas east of Tucson will see less chances of storms.

Moisture remains in place next week for daily chances of showers
and thunderstorms. With the large dome of high pressure over the
central part of the CONUS, there is the potential for an easterly
wave to move out of the Gulf of Mexico next week. At this time it
could be around Wed/Thu time frame.

High temperatures will be hanging around normal with day-to-day
variability.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Saturday morning through Sunday evening for
AZZ501>503-515.

&&

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