Area Forecast Discussion
Issued by NWS Tucson, AZ

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035
FXUS65 KTWC 231656
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
956 AM MST SAT JUL 23 2016

.SYNOPSIS...Isolated to scattered thunderstorms will occur mainly
east to south of Tucson today. An increase in deeper moisture will
then result in an upswing in thunderstorm activity during the
upcoming week. Expect well above normal temperatures again today
followed by a moderation in daytime temperatures next week.

&&

.DISCUSSION...Clear skies or mostly clear skies prevail across much
of southeast Arizona at this time. Some thicker mainly cirriform
clouds were across western Pima County, and these clouds were on the
northern periphery of a westward moving MCV entering the northern
Gulf of California from northwest Sonora. Dewpoints at lower
elevations valid 16Z ranged from the mid 50s-near 60. These temps
were nearly 5 degs higher versus 24 hours from Tucson westward into
western Pima County, but were a couple of degs or so lower east and
south of Tucson. Surface temps valid 16Z exhibited only a few degs
of change versus this time Friday, depending upon location.

23/12Z KTWC sounding total precip water value of 1.53 inches was
0.10 inch higher versus 24 hours ago. Stability parameters yielded a
more unstable regime versus Friday morning, with MUCAPE of 1230 J/kg
and Lifted Index of minus 5 as examples. However, the wind profile
especially in the surface-3km layer yielded markedly lower speeds
versus 24 hours ago. Regarding the synoptic scale, 23/12Z upper air
plots depicted a broad ridge of high pressure over the swrn CONUS,
with a 598 dm high analyzed just west of the southern California
coast, and a 597 dm high analyzed over northeast New Mexico. Light
wly/nwly winds prevailed in the surface-700 mb layer across
southeast Arizona, with moderate ely/sely flow in the 600-300 mb
layer.

There were differences between the 23/12Z Univ of AZ WRF-NAM and the
23/15Z HRRR regarding the development and evolution of showers/tstms
later today into the this evening. These solutions were similar with
suggesting that showers/tstms will initiate across the White
Mountains by early afternoon. The HRRR then depicted markedly more
showers/tstms to occur shortly thereafter south of Tucson, and
especially in an area from south-central Pima County ewd across
Santa Cruz County and into southwest Cochise County.

Meanwhile, the UA WRF-NAM kept the aforementioned area precip-free
until later this evening, and for this afternoon favored the White
Mountains/Chiricahua Mountains for showers/tstms to occur. At this
time, am inclined to favor the UA WRF-NAM scenario given recent HRRR
track record (e.g. last evening solutions depicting showers/tstms
into the Tucson metro area around daybreak this morning, etc.).

The official forecast depiction of scattered showers/tstms across
the White Mountains this afternoon/evening, and isolated
showers/tstms mainly southeast of Tucson, seems quite reasonable at
this time. High temps this afternoon will generally be a degree-or-
two warmer/hotter versus Friday, and will average about 6-10 degs
above normal.

Please refer to the additional sections for further detail.

&&

.AVIATION...VALID THRU 24/18Z.
Scattered -TSRA/-SHRA mainly east to south of KTUS this afternoon
and evening. KOLS has the best chance of -TSRA/-SHRA occurrence.
However, forecast confidence is not sufficiently high enough to
include in the TAF at this time. A slight chance of -TSRA/-SHRA
continues late tonight into Sunday morning, especially east to south
of KTUS. Brief wind gusts to around 40 kts and MVFR conditions will
occur with the stronger TSRA. Aviation discussion not updated for
TAF amendments.

&&

.FIRE WEATHER...Isolated to scattered thunderstorms mainly east to
south of Tucson today. Greater coverage of thunderstorms will then
occur starting Sunday and continue into next weekend. Outside of
gusty thunderstorm outflow winds, 20-foot winds will generally be
terrain driven and less than 15 mph.

&&

.PREV DISCUSSION /306 AM MST/...A large thunderstorm complex over
northern Mexico continued to decay early this morning, with debris
cloudiness across much of southeast Arizona. Latest HRRR solution
did not appear to be handling the current trends very well, so will
not place much merit on what the model has for later today in terms
of the thunderstorm potential. That said, the GFS and GEFS continued
to advertise a better flow pattern that will help bring deeper
moisture needed for thunderstorms northward this coming week. This
moisture increase will evolve as the upper high becomes more
consolidated over north-central NM and the four corners region in
the next day or so. The pattern then shifts with the upper high
amplifying and becoming centered over southern Nevada. This pattern
shift will bring a more north-east to easterly steering flow to the
area. Thus, helping steer thunderstorms developing in the higher
terrain of the Rim and White Mountains southwest in the lower
deserts. Otherwise, daytime temperatures will remain several degrees
above normal today, then moderate some as moisture and subsequently
thunderstorm coverage increase.

&&

.TWC Watches/Warnings/Advisories...None.

&&

$$

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