Flash Flooding and Heavy Rain in Arizona, August 7 to 8, 2022

Area Forecast Discussion
National Weather Service Flagstaff AZ
1000 AM MST Sun Aug 7 2022

.SYNOPSIS...Deep monsoonal moisture is returning to Arizona.
Scattered to widespread thunderstorms are likely each afternoon
through the middle of the week. Flash flooding will again be the
main threat, especially near recent burn scars.

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.UPDATE...Main change to the forecast this morning was to update
the POPs to include the ongoing shower activity taking place in
northern Gila County near Payson. These showers should decay
within the next hour or so.

For today, expect a busier day in regards to thunderstorm activity
compared to the last two afternoons. A weakening mesoscale
convective system (MCS), currently over south-central Arizona,
has pushed low- level moisture northward from the south increasing
surface dewpoints across Yavapai and northern Gila counties.
Dewpoints in these regions are currently sitting around the low
60s, increasing as you head towards the Colorado River Valley.
This moisture also looks to be pooling along the Mogollon Rim with
dewpoints nearing 60F. This coupled with mostly clear skies,
besides across northern Gila County, should result in a more
active thunderstorm day with scattered to widespread coverage
mainly along and south of the Mogollon Rim and into the White
Mountains.

Updated the POP a bit for this afternoon and evening to match
better with the most recent hi-res convective model guidance. The
HREF and SREF have storm's initiating off the higher terrain later
this morning and eventually progressing into Yavapai, Gila, and
western Coconino counties in the afternoon. Using the GFS/ECMWF
700-300 mb flow guidance, storm motion will likely move off the
higher terrain (the Rim) and head towards the southwest at around
5-15 mph for today. This morning's sounding from Flagstaff sampled
PWATs around 1.00 inch with decent CAPE in the mid-levels. 1 to 2
inch per hour rainfall rates can be expected during this time in
stronger cells as well as the potential for some hail and strong
outflow gusts. SPC does have portions of Yavapai and Gila counties
in a Marginal Risk for severe thunderstorms today.

Storm activity should decrease later tonight with another round
anticipated for Monday. The Flash Flood Watch remains in place for
Yavapai and northern Gila counties today.

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.PREV DISCUSSION /342 AM MST/...This evening's thunderstorm
activity across the lower deserts of Arizona and Sonora is a
testament to the ongoing moisture surge. Increasing atmospheric
moisture is enhancing the probability of widespread storms over
the coming days for northern Arizona. Similar to last night, an
impressive mesoscale convective system in northwestern Mexico is
sending moist outflow northward to Arizona. However, this system
is further north compared to yesterday's, indicating the build-up
of favorable moisture and instability across the Sonoran Desert.
Expect a day of thunderstorms across northern Arizona today, with
the exception of the region along the Arizona-Utah border. Storms
will likely form first over the high country before pushing off
to the west and impacting the low country. Areas south and west
of the Rim are especially subject to experience robust rainmakers
this afternoon. This is why a Flood Watch is in effect from noon
MST today through 5AM MST tomorrow morning for Yavapai County,
Gila County, and the Sedona area. While the flash flood risk is
heightened in the aforementioned regions, those in vulnerable
areas across the whole of northern Arizona should remain on alert.

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AVIATION...For the 18Z TAF package...Scattered to widespread
showers and thunderstorms are expected to develop after 18Z, mainly
along and south of a KGCN-KFLG-KPAN-KSOW line. Isolated storm
coverage is likely towards the north. Periods of MVFR/IFR VIS and
CIGS are anticipated in and around any storms with gusty and erratic
winds. Expect generally light winds with VFR conditions outside of
storms. Activity will likely subside after 03Z Mon. Aviation
discussion not updated for TAF amendments.

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FIRE WEATHER...Monsoonal moisture will return to northern Arizona
for today and Monday resulting in scattered to widespread
thunderstorm coverage. Greatest chances expected along and south of
the Mogollon Rim, including the White Mountains and across Yavapai
and western Coconino counties. Main threats include flash flooding
and gusty and erratic outflow winds. Activity will subside
overnight.

Tuesday through Thursday...An active monsoon pattern is expected to
continue through the week with daily chances for showers and
thunderstorms across northern Arizona. Temperatures remain near
average with generally light winds outside of storms.

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.FGZ WATCHES/WARNINGS/ADVISORIES...
Flood Watch through late tonight for AZZ008-018-037-038-108-118-
137-138.

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PUBLIC...LaGuardia/BJ
AVIATION...LaGuardia
FIRE WEATHER...LaGuardia

For Northern Arizona weather information visit
weather.gov/flagstaff