Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 201718

Area Forecast Discussion
National Weather Service Flagstaff AZ
1018 AM MST Sun Aug 20 2017

.SYNOPSIS...Expect the daily pattern of afternoon and evening
showers and thunderstorms to resume today as monsoonal moisture
returns to the region. This pattern will stick around through most
of next week.


.UPDATE...Minor updates were made to precipitation/thunderstorm
chances through tonight. The previous forecast handled expected
trends well with initial development along the rim, then moving to
the west and southwest. Edits were made to handle the light rain
activity ongoing over Yavapai County, and also to bump up precip
chances over western portions of Coconino and Yavapai counties
late this evening/overnight as confidence is increasing that
rain/thunder could persist well past sunset. Minor updates were
also made to wind, temperature, and sky grids through tonight.


.PREV DISCUSSION /425 AM MST/...Southerly flow will continue to
bring higher PW values north and west into the state for the next
several days. A weak area of low pressure moving into southwest
New Mexico early this morning is also helping to push moisture
northward and is providing some forcing to the eastern and
central zones. This weak synoptic lift has led to the development
of a few light showers from Flagstaff south and southeast.

We expect decent coverage today due to this airmass. Steering flow
supports early development along the Mogollon Rim, pushing west
and southwest in the afternoon. Steering flow becomes southerly
Monday and then southwesterly through the middle of the week.
Monday is likely to remain active, but a slight drying trend will
develop by Tuesday as flow turns southwest.

This flow pattern is due to a quasi-stationary low off the
southern California coast and high pressure over west Texas. By
the end of the week, this low is set to open up and move east.
There may be an uptick in activity Thursday as the low moves
across the state, then followed by drier conditons as westerly
flow and warmer mid-level temperatures develop behind the low.

Long story short, expect a return to low or medium grade monsoon
conditions for the next several days.


.AVIATION...For the 18Z package...SCT -SHRA will give way to more
numerous SHRA/TSRA developing with the highest coverage over the
Mogollon Rim and White Mountains. Stronger storms are expected to
diminish by around 03Z with ISOLD-SCT -SHRA continuing through much
of the night. Generally VFR conditions are expected with ISOLD MVFR
to IFR conditions in the stronger storms. Aviation discussion not
updated for TAF amendments.


.FIRE WEATHER...Isolated to scattered showers will persist this
morning. Deeper moisture returns to much of northern Arizona
today, with chances of mainly afternoon and evening thunderstorms
continuing through Monday.

Tuesday through Thursday...Thunderstorm chances persist through the
period, with generally light winds outside of storm activity.






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