Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 270340

Area Forecast Discussion
National Weather Service Flagstaff AZ
840 PM MST Mon Jul 26 2021

.SYNOPSIS...Scattered afternoon and evening showers and
thunderstorms are expected through Tuesday with near average
temperatures. Monsoonal moisture increases once again by
Wednesday, extending into the weekend, resulting in widespread
storm coverage across northern Arizona.


.UPDATE...Much of the activity across have diminished, aside from
a few isolated showers mainly over far northern Arizona. Minor
updates to the PoP grids this evening to incorporate radar trends
and latest hi- res guidance.


.PREV DISCUSSION /310 PM MST/...Taking a look out the window this
afternoon, mostly broken cloud cover is taking place with little
to no wind. Current radar is showing some isolated to scattered
thunderstorm activity popping up mainly west of I-17 into Yavapai
County as well as for a few areas north of I-40. The later start
to today`s convection could be the result from the earlier cumulus
development from this morning reducing daytime heating a bit.
Expect storm chances to continue, tapering by sunset this evening.

Global models, including the NBM, suggest much lesser shower and
thunderstorm activity for Tuesday, however we are hesitant to "go
all in" in this scenario. As the ridge of high pressure
transitions and strengthens just north of the Rockies, the
monsoonal flow pulls moisture a bit further west and north
extending into the deserts of California and Nevada. Yes, this
pattern reduces the moisture transport into Arizona with the
majority of the GEFS and EPS members showing a decrease in PWAT
values (1.1 to 0.6-0.7 inches by Tuesday afternoon), however low
to mid-level, lingering moisture will remain present across much
of the region during this time. This, coupled with enough daytime
heating, should be sufficient enough for storm development to
occur. No...not widespread, but some scattered coverage along the
higher terrain, including the Mogollon Rim, White and Chuska
Mountains, and the Kaibab Plateau. Hi-res guidance (HREF, HRRR,
and SREF) support this forecast thinking.

Moisture advection increases for Wednesday as the center of the
ridge settles over the Rockies, resulting in a return to more
widespread chances for thunderstorms across northern Arizona. PWAT
values increase back to the 1.0-1.2 inch range by Thursday with
higher confidence in flash flooding potential with 1-2 inch per
hour rainfall rates likely. Similar thunderstorm activity,
coverage, and impacts compared to last week is expected from
Wednesday into the weekend. Average temperatures with generally
light winds are also anticipated during this time.


.AVIATION...For the 06Z package...Mainly VFR condtions expected
through the TAF period. Showers and thunderstorms possible after
18Z, mainly in the high terrain. Brief periods of MVFR conditions
will be possible along with gusty and erratic winds in and around
thunderstorms. Winds will otherwise be light. Aviation discussion
not updated for TAF amendments.


.FIRE WEATHER...Isolated to scattered afternoon and evening
thunderstorms are expected through Tuesday. Moisture increases
once again for Wednesday resulting in a return to widespread
thunderstorms with the main threat being flash flooding,
especially on burn scar areas. Daytime temperatures will warm to
near-normal by mid-week with seasonal winds likely, outside of any
gusty and erratic outflows from storms.

Thursday through Saturday...Monsoonal moisture continues to
increase into the weekend with widespread chances for
thunderstorms across much of northern Arizona during this time.
Some storms can be severe, however higher confidence exists in the
main threat being flash flooding with rainfall rates of 1-2
inches per hour expected. Daytime temperatures will remain near-
normal with generally light winds likely.






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