Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 181055

Area Forecast Discussion
National Weather Service Tucson AZ
355 AM MST Tue Jul 18 2017

.SYNOPSIS...Conditions will remain favorable for widespread showers
and thunderstorms into Wednesday. Some drying may then reduce
thunderstorm coverage west of Tucson Thursday into Friday, but
locales east of Tucson will remain active. Widespread showers and
thunderstorms should return by early next week. Expect below normal
daytime temperatures for much of the area into early next week.


.DISCUSSION...IR satellite imagery depicted warming cloud tops
associated with a decaying MCS over south-central Arizona and over
portions of this forecast west-to-northwest of Tucson at this time.
Isolated showers and thunderstorms were moving westward across
western Pima County. Otherwise, mostly clear skies were noted east
of Tucson with mostly cloudy to cloudy skies elsewhere. Based on
satellite/radar trends as well as various high resolution models,
expect these showers/tstms to dissipate or move west of this
forecast area by 7-8 a.m. MST or so.

Several HRRR solutions as well as the 18/06Z Univ of AZ WRF-NAM were
in good agreement with the depiction of showers/tstms to redevelop
later this morning generally from the Tucson metro area eastward to
the New Mexico border. This is a similar scenario that occurred
Monday. At any rate, fairly widespread coverage of showers/tstms
should then prevail this afternoon into this evening.

Although widespread flash flooding is not expected to occur, the
ample available moisture should translate into the potential for at
least locally heavy rainfall. A threat also exists for a few
thunderstorms to produce locally damaging wind gusts. As has been
the case the past few nights, showers/tstms should favor locales
west-to-northwest of Tucson late tonight followed by dissipating
showers/ tstms early Wednesday morning. A similar scenario exists
late Wednesday morning into early Thursday morning.

The 18/00Z GFS/ECMWF/CMC and their respective ensembles continued to
depict a generally easterly mid-level flow regime to prevail
Thursday into Friday. These solutions depict the best coverage of
showers/tstms to generally prevail east-to-south of Tucson with
somewhat limited coverage of showers/tstms across western sections.

Thereafter, a pattern conducive to more widespread coverage of
showers/tstms appears in the offing starting Saturday and continuing
into early next week. The GFS and especially ECMWF depict the
presence of a pronounced inverted upper trough to approach from the
southeast this weekend, then become quasi-stationary over the area
next Monday. Thus, the official forecast continues with scattered to
numerous showers/tstms from Tucson eastward/southward Saturday thru
Monday mainly during the afternoon/evening hours; and, isolated to
scattered showers/tstms west of Tucson. Locally heavy rainfall and
brief damaging wind gusts should also occur.

Below normal daytime temperatures will prevail for much of southeast
Arizona into early next week.


.AVIATION...Valid thru 19/12Z.
Isolated -TSRA/-SHRA west of KTUS ending around 14Z-15Z this
morning. Scattered -TSRA/-SHRA developing KTUS vicinity east and
south late this morning, then scattered to numerous -TSRA/-SHRA this
afternoon into this evening. Expect -TSRA/-SHRA mainly west of KTUS
late tonight into early Wednesday morning. Otherwise, VFR conditions
with cloud decks generally 6k-12k ft AGL, and surface wind variable
in direction mainly less than 12 kts. Aviation discussion not
updated for TAF amendments.


.FIRE WEATHER...Expect fairly widespread coverage of showers and
thunderstorm into Wednesday. Isolated to scattered mainly afternoon
and evening thunderstorms will then prevail Thursday into Friday. A
favorable pattern for more widespread coverage of showers and
thunderstorms is expected to return by early next week. Otherwise,
20-foot winds will mainly remain below 15 mph with below normal high
temperatures continuing into this weekend.






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