Forecast Discussion

Forecast Discussion for TWC NWS Office
FXUS65 KTWC 152231

Area Forecast Discussion
National Weather Service Tucson AZ
330 PM MST Sun Sep 15 2019

.SYNOPSIS...Scattered thunderstorms east of Tucson ending early this
evening. Scattered showers and thunderstorms develop again Monday
and continue into Monday evening before dissipating. Markedly less
thunderstorm activity beginning Tuesday and prevailing into next
weekend. The best coverage of showers and thunderstorms should occur
Thursday. Seasonably warm daytime temperatures this week.


.DISCUSSION...Isolated showers and thunderstorms were occurring at
this time across portions of Greenlee/Graham/Cochise Counties east
of Tucson. Other isolated showers/tstms have occurred during the
past hour near the International border southwest of Tucson. Expect
any remaining showers/tstms the rest of this afternoon to remain
east to south of Tucson, and either dissipate or move eastward into
southwest New Mexico around or shortly after sunset. Dry conditions
to occur later tonight and into Monday morning.

Southwesterly flow aloft Monday to prevail ahead of a deepening
upper trough over the Pacific Northwest. Have noted several Univ of
AZ WRF solutions to favor a north-to-south oriented band of showers/
tstms to develop Monday afternoon west of Tucson. These showers/tstms
are then progged to move northeastward and encroach upon the Tucson
metro area Monday evening before dissipating. Global scale models
suggest more widespread coverage of showers/tstms to occur Monday
afternoon and evening before ending late Monday night.

At any rate, the official forecast continues with scattered showers/
tstms across much of this forecast area late Monday morning into
Monday evening. Expect any remaining showers/tstms to dissipate by
daybreak Tuesday. A low amplitude upper trough should exist Tuesday
across the western CONUS. There appears to be enough residual
moisture to justify isolated showers/tstms from Tucson eastward/
southward with dry conditions elsewhere. Any showers/tstms Wednesday
should be limited to mountains across eastern sections.

There were fairly distinct differences between the 15/12Z GFS/GEFS
and ECMWF/EPS regarding the potential for showers/tstms across this
forecast area on Thursday. The GFS/GEFS was markedly more robust
with precip potential, likely due to the northward import of
subtropical moisture into the area. However, the ECMWF/EPS shunted
the bulk of this deeper moisture plume further east into the
southern Rockies. Per coordination with neighboring WFO`s, have
maintained isolated showers/tstms Thursday east to south of Tucson.

Thereafter, the GFS/GEFS and ECMWF/EPS were quite similar with
depicting a light-to-moderate generally westerly flow aloft regime
to prevail across the area Friday into next Sunday. As a result,
expect mostly dry conditions across much of southeast Arizona
Friday into next Sunday with isolated afternoon/evening showers/
tstms confined mainly across the White Mountains.

Daytime high temperatures during this forecast package can generally
be characterized to average within a few degrees of seasonal normals
depending upon location.


.AVIATION...Valid through 17/00Z.
Isolated SHRA/TSRA mainly east of KTUS continuing into the early
evening, with cloud bases around 8k-12k ft MSL. TSRA/SHRA redevelop
tomorrow afternoon and areal coverage will extend across much of the
forecast area. SFC winds remain less than 12 kts through the period,
favoring a WLY-NWLY direction during the afternoon both today and
tomorrow. Stronger gusts will be possible around TSRA. Aviation
discussion not updated for TAF amendments.


.FIRE WEATHER...Expect showers and thunderstorms Monday afternoon
and evening across much of southeast Arizona. A drying trend then
occurs on Tuesday, which continues through the remainder of the
week. However, isolated mountain storms will still be possible
during the usual afternoon/evening timeframe. Light terrain driven
winds generally persist, except for breezier conditions on Thursday
afternoon across western Pima County.






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