Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 201722

Area Forecast Discussion
National Weather Service Flagstaff AZ
1020 AM MST Thu Jul 20 2017

.SYNOPSIS...Expect very active monsoon conditions for the next
several days. Local heavy rainfall capable of producing flash
flooding remains possible from stronger storms.

.DISCUSSION...The morning sounding at FGZ once again showed a very
wet atmosphere (0.96" Pwat) and a light east-southeasterly flow.
This means that storms will be slow moving and capable of producing
heavy rain (over the same area) which could lead to flash flooding.
An area of instability and weak rotation (MCV) was moving through
southern Navajo County and into northern Gila/southeastern Coconino
County this morning. Showers and isolated thunderstorms are
already in progress there. Another active day is expected across
northern Arizona!


.PREV DISCUSSION /327 AM MST/....Monsoon moisture will remain
entrenched across northern Arizona today. The primary change over
the past 24 hours is that high pressure in the mid-levels has
shifted further to the east. The result over Arizona will be for the
steering flow to point from south to north. Such a flow pattern
favors an increase in shower thunderstorm activity across northeast
Arizona as storms that form in the mountains and along the Mogollon
Rim send outflow boundaries across the Little Colorado River Valley,
as well as the Navajo and Hopi Nations. The northeast is a bit drier
so storms could produce wind gusts in excess of 50 mph. Otherwise,
local downpours of up to an inch will be possible. South of the
Mogollon Rim, under this steering flow, there likely will be a
downturn in activity with storms more isolated and tending to remain
over and near the mountains. We have adjusted the forecast grids to
account for this tendency. Still saturated soils across the broad
area encompassing Prescott and Payson with isolated 2+ inch
downpours and flooding possible.

From Friday onward...The steering flow remains south to north on
Friday with similar results as described above. A center of high
pressure then moves in from over the eastern Pacific for Saturday
and Sunday with the steering flow becoming northeast to
southwest. We will have to see how the moisture hangs in across
central Arizona but under this steering flow typically it is quite
active from the Mogollon Rim southward (similar pattern to that of
the past few days). Beyond the weekend, monsoon moisture remains
entrenched across Arizona with daily thunderstorms continuing.


For the 18Z package...Expect scattered to numerous showers and
thunderstorms along and north of the Mogollon Rim, with the
potential for scattered showers and thunderstorms initiating along
outflow boundaries south of the rim by mid afternoon. MVFR/IFR in
heavy rain will be possible under the strongest storms. Aviation
discussion not updated for TAF amendments.


.FIRE WEATHER...The active monsoon conditions will continue with
scattered to numerous showers and thunderstorms each day. Heavy rain
and gusty winds will remain the primary impact. Expect near average
temperatures across the area.

Saturday through Monday....Expect daily chances for showers and
thunderstorms. No significant changes in the weather pattern are






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