Special Weather Statement, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
352 PM MST SAT JUL 16 2016

.SYNOPSIS...Adequate moisture will provide scattered mainly afternoon
and evening showers and thunderstorms through Wednesday. A slight
decrease in daily coverage of showers and thunderstorms may then
occur Thursday into next weekend.

&&

.DISCUSSION...Scattered showers and thunderstorms were occurring
generally south of a Bowie-Benson-Tubac line at this time. Other
isolated showers/tstms were also ongoing across the White Mountains.
Rain amounts from alert gauges in central/eastern Santa Cruz County
and southwest Cochise County have yielded just a few hundredths of
an inch. Meanwhile, mostly clear skies prevailed elsewhere across
southeast Arizona at mid-afternoon.

The 16/12Z Univ. of AZ WRF-NAM/GFS were fairly similar with
depicting the best chance of measurable rainfall this evening to
occur south-to-southeast of Tucson. These solutions then depicted
what appears to be potentially a remnant MCV to be near the Tucson
metro area (just east of Tucson via the NAM; over Santa Cruz County
south of Tucson via the GFS) around daybreak Sunday. This scenario
definitely seems plausible given the darkening feature as per water
vapor imagery moving westward into east-central Sonora Mexico at
this time.

For this forecast issuance, have leaned toward a scenario for this
evening that suggests the bulk of the ongoing showers/tstms will
gradually decrease in coveage/intensity. Have then opted for
a slight chance of showers across much of the area late tonight. If
a remnant MCV exists early Sunday morning, the potential exists that
Sunday may be the proverbial down-day regarding precip chances as
the system moves north of the area.

However, given a somewhat low confidence in this scenario, have
essentially made only very minor adjustments to the inherited PoPs
Sunday and during much of the upcoming week. Thus, have continued
with scattered showers/tstms across much of the area Sunday
afternoon/evening, and similar coverage of showers/tstms Monday
through Wednesday during the afternoon hours. A slight chance of
showers/tstms exists during the late night/early morning hours.
Thereafter, slightly less daily coverage of showers/tstms should
exist Thursday into Saturday.

Have noted fairly large discrepancies between the operational 16/12Z
GFS/ECMWF during the next 7-day forecast period. For instance and in
general, the ECMWF was markedly wetter versus the GFS during
the afternoon/evening hours, whereas the GFS was markedly wetter
versus the ECMWF during the nighttime/early morning hours. There
were several nighttime periods that the ECMWF depicted precip-free
conditions area-wide, while the GFS suggested isolated to perhaps
scattered coverage of showers/tstms for any given nighttime period.

At any rate, daytime temps Sun-Wed will be quite close to seasonal
normals followed by a gradual warming trend Thur-Sat.

&&

.AVIATION...VALID THRU 18/00Z.
Scattered -TSRA/-SHRA this evening mainly south-to-southeast of KTUS,
then isolated -SHRA across the area late tonight into Sunday morning.
Expect scattered -TSRA/-SHRA to return Sunday afternoon. Brief wind
gusts to 45 kts and MVFR conditions may occur with stronger TSRA.
Surface wind will generally be variable in direction less than 12
kts thru the period. However, surface wind east of KTUS this evening
and Sunday afternoon will be nwly at 10-20 kts with gusts to 25 kts.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Adequate moisture will lead to scattered mainly
afternoon and evening thunderstorms through at least Wednesday. A
slight decrease in daily coverage may then occur starting Thursday
and continuing into next weekend. Outside of thunderstorm winds,
expect typical diurnal 20-ft wind patterns. However, gusty northwest
winds should occur Sunday and Monday across the Upper Gila River
Valley including Safford.

&&

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

&&

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