Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 271620

Area Forecast Discussion
National Weather Service Flagstaff AZ
920 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.


Have tweaked pops and qpf to better match short term model
forecasts and radar trends. Otherwise forecast remains on track
and no significant updates are expected before the afternoon
product suite.


.PREV DISCUSSION /233 AM MST/...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.




.FGZ WATCHES/WARNINGS/ADVISORIES...Excessive Heat Warning until 11 PM MST Thursday FOR AZZ005-006.




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