Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 191642
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
942 AM MST Tue Sep 19 2017

.SYNOPSIS...Dry conditions across much of the area with seasonably
warm temperatures through Wednesday. A strong low pressure trough
will then bring isolated showers and thunderstorms, gusty winds and
a cooling trend Thursday into Friday. Expect dry conditions with
below average temperatures this weekend.

&&

.DISCUSSION...A zonal flow across the region with dry conditions
north of us and moisture still available in Sonora. We`ll continue
to see just enough for isolated thunderstorms near the far
southeast and eastern mountains. Otherwise, a deepening trough
will dominate weather through Western states. For us that will
translate into gusty winds and a cooling trend later this week, as
per the previous discussion below.

&&

.AVIATION...Valid thru 20/18Z.
A few -TSRA/-SHRA may occur near the international border
southeast of KTUS and perhaps near KDUG this afternoon. Forecast
confidence is too low to include in the KDUG TAF. Otherwise,
clear skies will prevail west to north of KTUS. A few to
scattered clouds around 8k-12k ft AGL will occur southeast of KTUS
this afternoon and evening. Surface wind late this morning
through the early evening hours will be swly to nwly at 13-20 kts
with gusts to near 30 kts. Surface wind mainly less than 12 kts at
other times. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...There will continue to be a slight chance of
afternoon and evening showers and thunderstorms mainly east and
south of Tucson through Friday, before a drying trend takes place
this weekend. A deepening upper trough over the western United
States will result in gusty southwest winds, especially during the
afternoon and evening hours through Saturday. The strongest winds
are expected on Thursday and Friday. Near normal high temperatures
will continue through Thursday, cooling to below normal levels this
weekend.

&&

.PREV DISCUSSION...Despite a drier westerly flow aloft, models
showed enough moisture near the International Border to support a
slight chance of showers and thunderstorms southeast of Tucson
through Wednesday. Thereafter, models deepen a system over the
Intermountain West Thursday into the weekend with varying amounts
of moisture advecting into southeast Arizona in advance of it. The
latest GFS solution suggested that the bulk of this moisture will
remain east of the area. This solution differed from the ECMWF
model which showed deeper moisture increasing east through south
of Tucson Thursday into Friday. Given the wide spectrum of
solutions, will keep the trend of increasing rain chances for
Thursday and Friday in the forecast for now. Otherwise, the system
will bring strong and gusty winds, especially Thursday and
Friday, along with noticeably cooler temperatures.

&&

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

&&

$$

Meyer

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