Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 260431
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
930 PM MST SUN SEP 25 2016

.SYNOPSIS...A persistent low pressure system will bring gusty winds
into Monday, along with a chance of showers and thunderstorms
through midweek. A gradual drying trend will then occur during the
latter part of the week, with dry conditions returning area-wide
next Sunday. Expect cooler temperatures Monday, then daytime
temperatures returning closer to normal late in the week.

&&

.DISCUSSION...A few showers and thunderstorms developed this evening
near the International Border but have since dissipated. Latest
models still indicated showers and a few thunderstorms on the
increase later tonight and Monday. The wind will be the main concern
as a strong easterly flow strengthens by morning and continues
through the day Monday. The other weather story will be the much
cooler daytime temperatures for tomorrow. That said, the current
forecast handled the trends well so no updates necessary this
evening. Please refer to the additional sections for more details.

&&

.AVIATION...Valid through 27/06Z.
A few -SHRA/-TSRA this evening near the International border south
of KTUS, then -SHRA/-TSRA to increase from southeast to northwest
across the area late tonight into Monday afternoon. MVFR conditions
with occasional higher terrain obscurations especially Monday.
Otherwise, cloud decks will mainly be 10k-15k ft MSL thru the period.
Surface wind tonight into Monday afternoon will be ely/sely at 12-25
kts with gusts to near 40 kts. Aviation discussion not updated for
TAF amendments.

&&

.FIRE WEATHER...Scattered showers with isolated thunderstorms
area-wide late tonight into Monday. Stronger thunderstorms may occur
Tuesday, especially from Tucson westward into western Pima County. A
chance of showers and thunderstorms exists Wednesday into Thursday
mainly east of Tucson, then showers and thunderstorms Friday into
next weekend should be limited to near the New Mexico border.

Expect strong and gusty east winds tonight into Monday night. 20-
foot winds will likely be mainly in the range of 15-25 mph with
higher gusts. Winds should decrease Tuesday followed by elevated
southwest afternoon winds during the latter part of the week.

&&

.PREV DISCUSSION...The various 25/12Z NWP model suite remained
consistent versus previous solutions regarding the overall weather
regime during the upcoming week. A low pressure system will become
quasi-stationary over central Baja California Monday. A tight mid-
level gradient will translate to gusty ely/sely winds later tonight
into Monday. A wind advisory is in effect from 5 am to 4 pm
MSTMonday for portions of the Tucson metro area, and other locales
southwest to southeast of Tucson.

Moisture will increase across the area later tonight into Monday as
well, and only minor adjustments were made to the gridded data PoP
values during much of this forecast period. Thus, there is a slight
chance of showers and thunderstorms this evening mainly near the
International border adjacent Santa Cruz/Cochise Counties. Precip
chances will increase from southeast-to-northwest late tonight into
Monday. This will translate into scattered to perhaps numerous
showers and a slight chance of thunderstorms Monday. Some decrease
in coverage of showers/tstms to occur Monday night into early
Tuesday.

The upper low is progged to move northward into southwest AZ Tuesday
afternoon. 25/12Z Univ of AZ WRF-NAM and GFS remained similar versus
previous solutions with suggesting that stronger thunderstorms may
occur Tuesday afternoon, particularly from Tucson westward into
western Pima County. The projected storm trajectories also suggest
the potential for blowing dust Tuesday afternoon, perhaps along the
Interstate-10 corridor from northwest of Tucson into southern Pinal
County.

A deep sly flow regime should prevail Wednesday as the upper low
weakens west of the area. Some mid-level drying my encroach upon
southern sections, and enough moisture should exist for a slight
chance of showers/tstms area-wide into Wednesday night. The flow
aloft Thursday is presently progged to become increasingly swly, and
the deeper moisture is depicted to arc from northern AZ sewd into
southwest New Mexico. A slight chance of showers/tstms continues
Thursday generally from Tucson eastward to the New Mexico border.

Thereafter, the deterministic 25/12Z GFS/ECMWF were similar Fri-Sun
with depicting increasing swly flow aloft in response to a deepening
low pressure system over the Pacific Northwest. This regime will
likely result in substantial drying across this forecast area, with
precip-free conditions to return area-wide next Sunday.

High temps Monday are forecast to be about 8-15 degs cooler versus
this afternoon. A warming trend will then occur Tue-Thur followed by
no significant change in daytime temps Fri-Sun. The upshot is that
high temps Thur-Sun will return closer to seasonal normal for late
Sep/early Oct.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
    Wind Advisory from 5 AM to 4 PM MST Monday for AZZ503-504-507-
      508-515.

&&

$$

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