Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 130420
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
920 PM MST Tue Sep 12 2017

.SYNOPSIS...Isolated afternoon and evening thunderstorms will
continue mainly over the higher terrain east of Tucson, becoming
breezy to locally windy on Thursday and Friday. Moisture then begins
to increase on Sunday into early next week expanding thunderstorm
coverage.

&&

.DISCUSSION...The 13/00Z 500mb upper air plot shows a 591dm high
situated over southeastern Arizona and this feature resulted in
record high temperatures in multiple locations this afternoon. Drier
air has also advected into the far southeastern portion of the
state. Satellite derived precipitable water indicates an area of 0.5-
0.7" spanning from Safford to Sierra Vista stretching toward the New
Mexico bootheel.

Although most of our area experienced fair weather today, enough mid-
level moisture remained for isolated thunderstorms to develop over
the White Mountains as well as a few storms in central Pima County.
This activity has since greatly diminished in coverage and PoPs have
been adjusted down to account for radar/satellite trends. Model
guidance suggests a dry forecast through tonight with clear to
partly cloudy skies. Please see the previous discussion for further
details on the rest of this week and the week ahead.

&&

.AVIATION...Valid thru 14/06Z.
SKC and variable winds less than 10 kts are expected through
tonight. WLY/NWLY SFC winds increase Wednesday afternoon 10-20 kts
with gusts to 25 kts especially northeast of KTUS, and a slight
chance of -TSRA/-SHRA mainly east of KTUS. Aviation discussion not
updated for TAF amendments.

&&

.FIRE WEATHER...Isolated afternoon and evening showers and
thunderstorms mainly east of Tucson through Saturday. There is a
slight chance of showers and thunderstorms area wide early next
week. Gusty southwest to northwest winds especially east of Tucson
Wednesday into Friday as a couple of troughs move north of the area.
Otherwise, 20-foot winds will generally be terrain driven at less
than 15 mph.

&&

.PREV DISCUSSION /255 PM MST/...Looking ahead, confidence is
increasing that we will begin to transition away from our typical
monsoon pattern in the coming days. Though some moisture will linger
for a few days, the upper pattern will do well to get rid of our
easterly flow regime by the coming weekend.

To get to that point however, we`ll have to deal with a few weak
troughs swinging north of the area. Low pressure off the CA coast
will migrate eastward on Wednesday and open up into the larger scale
flow on Thursday as it moves through the Great Basin. We may see a
few more showers or storms across the Whites each day as this
occurs, but most of the CWA will remain dry. However, a tightened
pressure gradient will lead to slightly elevated southwest winds,
especially on Thursday.

A stronger trough is progged to dig south out of the Pac NW and kick
the first quickly eastward Friday into Saturday. This trough remains
slightly further north of the area than the first, but breezy
southwest winds are once again a good bet. Have maintained a slight
chance of showers and storms mainly across eastern areas Friday into
Saturday.

There are hints of "tropical trouble" early next week, however
confidence remains low as medium-range models still cannot come to a
consensus on the evolution of the next tropical system. PoPs were
increased a bit especially for eastern zones Sunday and Monday,
expecting that we may have a moisture surge ahead of the system for
at least a slight chance of showers and thunderstorms area-wide each
day. Past that, kept PoPs in the slight chance category as the track
of this system has yet to be determined.

Today will be the warmest day out of the next 7. Look for a few
degrees of cooling for Wednesday, with more seasonable temperatures
on tap Thursday into early next week. Lower dewpoints will help our
overnight lows out a bit as well, with upper 60s possible across the
Tucson metro Saturday and Sunday mornings.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None

&&

$$

Howlett/Francis/French

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