Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 270933

Area Forecast Discussion
National Weather Service Flagstaff AZ
233 AM MST WED JUL 27 2016

.SYNOPSIS...The high pressure ridge is building westward into a
position that effectively blocks Monsoon moisture from moving up
into northern Arizona. Rather we will see a drier airmass move
into Arizona from the north heralding a low grade Monsoon weather
pattern with only a few thunderstorms developing along and north
of the Mogollon Rim country from Wednesday through Friday. Drier
air will lead to hot temperatures in the Grand Canyon region
through Thursday. Another Monsoon moisture surge is forecast to
start this weekend with increasing chances for showers and
thunderstorms through the weekend with storm activity lasting into
next week.


.DISCUSSION...The subtropical ridge will build westward blocking
our south to north Monsoon moisture tap and at the same time
advecting in drier air into Arizona from the north. Drier air will
bring warmer temperatures, higher cloud bases, and lower chances
for thunderstorms. Hot temperatures are forecast for the Grand
Canyon region with an Excessive Heat Warning in effect from Today
through Thursday. This dry pattern will not last long as the
ridge shifts eastward and a low pressure system moves across the
mouth of the Gulf of California. The track of this low will likely
generate a pressure wave causing a moisture surge northward up
into Arizona over the weekend.

Long range models continue to show this deep Monsoonal moisture
surge working its way into the state from south to north on
Saturday and Sunday. Expect increasing chances and a higher
coverage of showers and thunderstorms pushing northward each day.
Forecast guidance also shows climatologically excessive moisture
amounts on Monday and Tuesday as shown by precipitable water
totals in the 1.2 to 1.5 inch range. These exceedingly high
moisture totals may hinder convective development during the day
due to extensive cloud cover reducing the surface heating
convective trigger. Temperatures will also run several degrees
cooler through Wednesday.


.AVIATION...For the 12z Package. Expect mostly VFR conditions with
just isolated to scattered showers and thunderstorms possible btwn
18z - 02z Thu and mainly over the Mogollon Rim region. Storm
activity will diminish around sunset. Aviation discussion not
updated for TAF amendments.


.FGZ WATCHES/WARNINGS/ADVISORIES...Excessive Heat Warning from 8 AM this
morning to 11 PM MST Thursday for the Grand Canyon region below
4000 feet elevation.




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