Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 141732

Area Forecast Discussion
National Weather Service Flagstaff AZ
1032 AM MST Thu Sep 14 2017

.SYNOPSIS...A low pressure system moving through the region today
will bring a cooler, windy, and showery day to northern Arizona. A
few thunderstorms that develop could become strong to severe. A
flash flood watch is in effect for far northwestern Arizona
through early this evening. Dry and cool weather will follow for
Friday, lasting through the coming weekend.


Increased chances for precipitation as the closed low continues to
track towards the area. Discrete organized convection can be
found along the Mojave border with Coconino and Yavapai counties.

These longer lasting storms ahead of peak heating are strong
indications of an organized environment that will allow for
stronger and potential severe thunderstorms as diurnal heating
combines with the upper level instability to create stronger lapse
rates in an environment favorable for organized storm formation.

Main threat today continues to be damaging winds from outflows of
storms with a lesser chance for large damaging hail. It should
also be noted there is a very slight chance for an isolated tornado




Low pressure is centered over inland southern California early
this morning and moving east. Lift ahead of the trough has already
supported a few thunderstorms across eastern Arizona overnight.
The trough will head east through the southern tip of Nevada today
and then northeast into southern Utah by this evening. Moisture
remains somewhat limited but sufficient when combined with dynamic
lift to produce scattered to numerous showers and storms today
mainly from the Mogollon Rim north. Deep layer 0-6 km wind shear
values of 35 to 45 kts will promote some strong and long-lived
updrafts, with perhaps some rotating updrafts, leading to an
enhanced threat for severe thunderstorm development. The most
likely area for severe storms is the northern third of our area
roughly from Grand Canyon east across the Hopi Mesas and north to
Utah. Large hail and damaging winds of 60+ mph are the concerns.

Though moisture is rather limited and storm coverage is not
expected to be widespread, we feel the threat for strong, heavy
rain producing cells warrants a flash flood watch for the
northwestern corner of the state. This includes Grand Canyon,
Supai, Page, and Antelope Canyon. The threat for thunderstorms
will end quickly this evening as much drier air spreads east
across the state behind the trough passage. The trough will also
bring windy and cooler weather. Expect frequent wind gusts today
in the 30-40 mph range.

Subsequent troughs will move through the western U.S. this weekend
keeping temperatures cool, though dry weather will continue. A
deeper trough looks to affect the west next week with a likely
return of unsettled weather.


.AVIATION...For the 18z package... Morning convection has cleared
out with a few lingering showers north of KGCN. After 18z, scattered
to numerous SHRA/TSRA especially along/north of Mogollon Rim.
MVFR/IFR conditions and erratic outflow winds will be possible in
the vicinity of the stronger storms. In addition, south to southwest
winds with gusts between 25-35 knots are forecast 17Z-02Z. SHRA/TSRA
ending from west to east after 02Z. Aviation discussion not updated
for TAF amendments.


.FIRE WEATHER...A low pressure system will cross the area today
bringing increasing chances for showers and thunderstorms, and
gusty south to southwest winds. Dry and cooler weather will
arrive for Friday and Saturday, with breezy conditions continuing
Friday. A return of moisture is possible in the White Mountains
region Sunday and Monday, with most other areas remaining dry.


.FGZ WATCHES/WARNINGS/ADVISORIES...Flash Flood Watch until 7 PM MST this evening FOR AZZ004>006-009.




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