Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 301659

Area Forecast Discussion
National Weather Service Flagstaff AZ
959 AM MST TUE AUG 30 2016

.SYNOPSIS...Monsoon moisture will start to gradually return to
eastern Arizona starting today, with isolated to scattered
showers and thunderstorms in the forecast across the region
through the remainder of the work week. A drying trend will move
into the region starting on Saturday with a Pacific trough
bringing dry southwesterly flow into northern Arizona.


.UPDATE...Lower level moisture has increased in the past 24 hours
across portions of central and southeast Arizona, including
northern Gila, southern Navajo and Apache counties. Some isolated
showers and storms have already developed over the White Mtns as
of 950am, and the steering flow from northeast to southwest should
push this activity into portions of northern Gila over the next
several hours. This trend is handled in current forecasts, and
only minor updates are anticipated today. Remainder of discussion
below still applies.


.PREV DISCUSSION...(Today through Wednesday) Northern Arizona is
currently positioned on the downstream side of an upper level
ridge resulting in a light northeast flow across the region. This
flow will keep the best moisture along and south of the Mogollon
Rim today. In addition, a stable layer around 500 mb will help
limit thunderstorm development as well. With that said, the
forecast calls for a slight uptick in convection as compared to
yesterday. In general, expect scattered storms along the eastern
Mogollon Rim and White Mountains, with more isolated activity
possible over other higher terrain locations from Flagstaff
eastward. On Wednesday, chances for storms increase as moisture
slides in under the ridge from the southeast. With that said, the
atmosphere remains quite stable, so still expecting low to
moderate grade monsoon activity for most places. Model forecasts
continue to favor the eastern Mogollon Rim and White Mountains,
with more isolated activity elsewhere.

(Wednesday night through Monday) Monsoon moisture will peak over
northern Arizona Thursday through Friday. Each afternoon is
forecast to have a chance of showers and thunderstorms develop,
primarily over the higher elevations of northern Arizona. Marginal
instability and shear parameters could lead to stronger storms
developing over northwestern Coconino county Thursday afternoon,
and over the higher terrain of northern Arizona Friday afternoon.
The main threats will be small hail and gusty winds. By Saturday,
the medium range models diverge with their solutions. The latest
GFS drys out all of northern Arizona whereas the ECMWF keeps
monsoon moisture lingering with another day of showers and
thunderstorms forecast. Given the model to model and run to run
inconsistencies, will keep low POPS in for Saturday afternoon.
Sunday through Monday, a long wave trough is forecast to develop
over the western CONUS. This will lead to dry southwesterly flow
developing over northern Arizona, with little to no precipitation
forecast each day. Temperatures will be near to slightly below
normal through the period.


.AVIATION...For the 18Z package...VFR conditions will prevail
across the majority of northern Arizona over the next 24 hours.
from 18Z Tue to 02Z Wed, scattered showers and thunderstorms are
forecast along the White Mountains and Eastern Mogollon Rim,
moving toward the southwest and affecting portions of northern
Gila county in the afternoon. Activity more isolated in nature
elsewhere. Aviation discussion not updated for TAF amendments.






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