Areal Flood Warning 1, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
631 PM MST Thu Jul 22 2021

.SYNOPSIS...Scattered showers and isolated thunderstorms begin to
expand in coverage from east to west overnight. The threat of
flash flooding will increase into the weekend as thunderstorms
occur across much of northern Arizona.

&&

.UPDATE...Widespread shower and thunderstorm activity continues
across a significant portion of northern Arizona this evening.
Flooding has been identified in Show Low, Flagstaff and other
locations across the region. Do not walk or drive through flood
waters. It only takes 6 inches of fast moving water to knock a
person over and carry them away, 12 inches to carry away a small
vehicle and 18 to 24 inches to carry away most large SUVs, trucks
and vans. Most importantly, it is impossible to see if the road
has washed out and just how deep the water has cut into the ground.
Turn around, don't drown!

&&

.PREV DISCUSSION /129 PM MST/...There is a significant threat of
flash flooding from today through Saturday, and possibly Sunday.
Severe thunderstorms are also possible from Friday afternoon into
the overnight hours.

High pressure remains entrenched over the Four Corners today and
is bringing clockwise flow aloft across northern Arizona.
Thunderstorms that formed over the high terrain are slowly
beginning to move into the lower elevations on light steering
flow. Localized heavy rainfall has been observed with these
isolated to scattered thunderstorms. Expect expanding coverage of
showers and storms throughout the remainder of the afternoon and
evening hours today.

A weak disturbance is rotating around the high pressure this
afternoon in the central Rocky Mountains and is progged to enter
the Four Corners area later this evening. Accompanying this will
be enhanced dynamics to support overnight convection, beginning
first in Apache County this evening and spreading southwestward
overnight. High resolution guidance is showing high chances for
widespread rainfall tonight in mainly northeastern and east-
central Arizona, with areas of embedded heavy rainfall. The
current Flash Flood Watch remains in effect until late Saturday
evening for a prolonged threat of flash flooding.

There is moderate confidence in a slight downturn in activity by
mid to late Friday morning, but another round of afternoon/evening
thunderstorms on Friday are likely. A second dynamic system, this
time an inverted trough moving westward from the southern
southern Rockies, will then provide enough support for another
round of overnight heavy rainfall Friday night. The inverted
trough is also progged to create enough wind shear to support
prolonged updraft development over northern Arizona on Friday. The
result would be a combination of heavy rainfall leading to flash
flooding, but also some severe thunderstorms. The severe
thunderstorm threat should be monitored even into Friday night on
the leading edge of another large storm complex moving into the
state from the east.

Significant flash flooding is again possible into Saturday as an
already saturated ground is favored to produce enhanced runoff.
The synoptic setup on Sunday is following a trend that began
yesterday where the inverted trough stalls out over southern
Arizona and continues to produce heavy rainfall on Sunday. The
current Flash Flood Watch will have to be monitored against
growing confidence in these conditions for later this weekend.

Scattered thunderstorm coverage remains in the forecast early next
week, but a bit less than what is expected over the next few
days, as moisture remains over northern Arizona.

&&

.AVIATION...For the 06Z package...Shra/tsra coverage increasing
across eastern Arizona and spreading west through the night. Areas
of MVFR/IFR possible. Gusty outflow winds near any storm activity
with otherwise light winds. Aviation discussion not updated for
TAF amendments.

&&

.FIRE WEATHER...There is a significant flash flood potential this
afternoon through Saturday night.

Scattered to numerous afternoon and evening showers and
thunderstorms are expected today through Saturday with storms
continuing into the overnight hours. Widespread wetting rain is
likely with embedded areas of heavy rain. Storm coverage will
begin to decrease by early next week.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...Flash Flood Watch through Saturday evening FOR AZZ006>008-
011>018-037-038-040.

&&

PUBLIC...Kobold/NL
AVIATION...Kobold
FIRE WEATHER...NL

For Northern Arizona weather information visit
weather.gov/flagstaff

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