Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 201614

Area Forecast Discussion
National Weather Service Flagstaff AZ
914 AM MST SAT AUG 20 2016

.SYNOPSIS...Monsoon moisture will remain in place with the
potential for shower and thunderstorm activity continuing through
the middle of next week.


.UPDATE...This morning`s sounding from Flagstaff shows cooling of
about 1 to 2 degrees Celcius in the mid-levels compared to
yesterday. This will allow for a bit more instability today, with
showers and storms first firing in the White Mountains around 10
to 11 AM MST, and then farther northwest along the Mogollon Rim
beginning after 11 AM.

The steering flow is northeast to southwest, so we will see storms
that develop on the Rim move down into Yavapai and northern Gila
Counties this afternoon. We may see an MCS develop this afternoon
across Yavapai County as storms move off the Mogollon Rim. The
main threat with storms today will be heavy rain, which could lead
to localized flash flooding, especially across Yavapai County.
There will also be a threat for marginally severe hail and gusty
winds with the strongest storms.

The PoP forecast was updated to increase storm chances across
Yavapai and northern Gila counties this afternoon, otherwise,
everything else looks good.


.PREV DISCUSSION /331 AM MST/...A low-level high pressure
circulation will remain positioned over south central Arizona
through Sunday. The circulation around the high will continue to
push moisture residing over the Gulf of California/northwest
Mexico into Arizona and across the Mogollon Rim. In addition, a
weak trough aloft will provide a cooler than normal mid-level air
mass and weak upward motion. As daytime heating progresses expect
a decent chance of showers and storms both today and Sunday from
the Mogollon Rim south with lower chances in drier air to the
north. The main threat the next two days will be isolated heavy

From Monday onward...As westerly flow develops through a deep
layer, low-level drying and mid-level warming should start to
stabilize the air mass over northern Arizona. However, some model
conflicts exist. The European model hangs on to just enough
moisture for a decent chance of showers and thunderstorms through
the week. The GFS is drier with less convective activity. The
development of westerly flow aloft usually brings more stable
conditions and favors the less convective GFS solution. As a
result, the forecast grids will contain a lower chance of showers
and thunderstorms from Monday onward but complete shut off isn`t
likely due to lingering moisture.


.AVIATION...For the 18Z package...Deeper moisture and greater
instability over the southern part of the forecast area will support
robust thunderstorm development. Sct SHRA/TSRA will develop along
and south of the Mogollon Rim early this afternoon...becoming
SCT/NMRS late this afternoon through 03Z as the storms slowly move
toward the south and west. Generally ISOLD -TSRA expected north
and east of a KGCN-KINW line through tonight. Expect MVFR
conditions with the stronger storms. Aviation discussion not
updated for amendments.






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