Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 272206

Area Forecast Discussion
National Weather Service Tucson AZ
305 PM MST TUE SEP 27 2016

.SYNOPSIS...An area of low pressure aloft will provide a chance of
showers and thunderstorms through Thursday. A slight chance of
showers and thunderstorms Friday will exist east of Tucson, then dry
conditions will prevail this weekend into early next week.


.DISCUSSION...Scattered showers and thunderstorms extended from the
central/southern portion of the Tohono O`odham Nation southeastward
into western Santa Cruz County at this time. Movement of these
showers and thunderstorms was to the north at 25-30 mph. This area
of showers/tstms is well handled via the 27/12Z Univ of AZ WRF-NAM
and GFS. The 27/20Z HRRR was too far southeast with this area of
showers/tstms valid at the current time.

Expect scattered showers/tstms this evening ahead of an upper low
pressure system centered over far northwest Sonora Mexico. The upper
low is progged to fill while moving northwest into southern
California Wednesday morning. The hi-res models suggest that
isolated showers/tstms will continue late tonight. A north-to-
south axis of deeper moisture will maintain isolated to scattered
showers/tstms mainly from Tucson eastward Wednesday and Wednesday

Meanwhile, Tropical Storm Roslyn located at 18.8N/116.6W (or about
515 miles WSW of the southern tip of Baja California) valid 2 PM MST
this afternoon is expected to weaken to a remnant low in about 24
hours. However, the 27/12Z GFS/ECMWF/CMC depict some moisture from
this system to be entrained northeastward across the area Thur.
Thus, precip chances are expanded further west Thur versus Wed to
include the entire forecast area.

Isolated to scattered showers/tstms should continue Thur evening,
then a drying trend will ensue from west-to-east Friday as
southwesterly flow aloft increases. A slight chance of showers/tstms
continues across eastern sections Friday afternoon/evening.
Thereafter, the GFS/ECMWF/CMC were similar with depicting a
deepening upper low over the Pacific Northwest this weekend, then
moving this system eastward across the northern Rockies/northern
CONUS Plains Mon-Tue. Stronger westerly flow aloft will shunt the
deeper moisture well east of the area. Thus, dry conditions to
prevail Sat-Tue.

High temps Wed are forecast to be about 5-10 degs warmer versus
temps achieved this afternoon. A few degs of additional warming will
occur Thur followed by no significant change in daytime temps Fri-
Sat. A very minor moderation in daytime temps is on tap early next
week, with high temps trending a few degs below normal.

A warming trend will occur Tue-Thur followed by no significant
change in daytime temps Fri-Mon. The upshot is that high temps
Thursday into early next week will trend closer to seasonal normals
for late Sep/early Oct.


.AVIATION...Valid through 29/00Z.
Scattered -TSRA/-SHRA this evening followed by a slight chance of
-TSRA/-SHRA late tonight into Wednesday morning. Isolated to
scattered -TSRA/-SHRA to prevail Wednesday afternoon KTUS vicinity
east to the NM border. Otherwise, cloud decks generally 6k-10k ft
AGL, and surface wind easterly to southerly at 5-15 kts with gusts
to 25 kts. Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...A chance of thunderstorms exists area-wide through
Thursday evening, then a drying trend will begin late Thursday and
continue into this weekend. A slight chance of showers and
thunderstorms Friday will continue east of Tucson followed by dry
conditions Saturday through next Tuesday. Expect occasionally gusty
east winds through Thursday, then normal diurnal wind trends to
prevail Friday into early next week.






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