Flash Flood Watch 5, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
948 PM MST Sun Jul 23 2017

.SYNOPSIS...A Flash Flood Watch continues across northern Arizona
through midnight. Heavy rainfall with flash flooding is possible
from stronger storms. Active monsoon conditions are expected to
continue Tuesday. A decrease in storm coverage should develop
starting Wednesday, especially across western and central
Arizona.

&&

.DISCUSSION...The flash flood watch covering the entire area
remains in effect through midnight. The bulk of the action this
evening has been over Yavapai County where a flash flood warning
remains in effect until 11:15pm tonight. Area creeks, streams and
rivers are running high and rises are currently being observed on
the Agua Fria River. This water could make it as far south as
Black Canyon City by late tonight. Otherwise, additional scattered
shower and thunderstorm activity is ongoing across a large
portion of the area. Latest model guidance indicates this will
likely continue through the overnight hours with an inverted
trough positioned to the south and west.

How widespread convection will be on Monday still remains in
question. Model soundings show a nearly saturated column which
would promote more in the way of cloud cover, cooler temperatures,
and light to moderate rainfall. However, overnight trends will
have to monitored as any breaks in the cloud cover and heating
would result in the development of more widespread storms across
northern Arizona on Monday. The next shift will fine-tune this
portion of the forecast for the morning package.

&&

.PREV DISCUSSION /249 PM MST/...A flash flood watch continues
for all of Apache, Coconino, Navajo, Yavapai, and northern Gila
Counties until midnight tonight. We have already issued several
Flash flood Warnings and Flood Advisories for southern Coconino
County. Storms have been very slow moving, and observed rainfall
has been over 1.5 inches with some of the stronger storms. Radar
indicates outflow boundaries are moving southward and westward
into northeast Yavapai county now, and an active period of weather
is expected there through mid evening.

For tonight and Monday...Progs continue to show an inverted
trough feature moving from southeast AZ through western AZ, with
abundant moisture persisting. Storms could persist into the
overnight tonight with the help of the feature. The storm steering
flow to switch from southeasterly tonight to southerly Monday. On
Monday, forecast soundings show a nearly saturated atmosphere
through a deep layer. Rain chances are high, but the amount of
cloud cover could act to hold down instability and decrease storm
intensity, rainfall rates and flash flood potential. Stay tuned as
this part of the forecast remains uncertain and could change.

Tuesday - the inverted trough is forecast to move north of the
state, with slightly lower precipitable water values over the
region. Looking for a more typical monsoon pattern, with scattered
afternoon storms moving SW to NE.

Wednesday & Thursday - models indicating a drier air mass and some
warming in the mid levels. Not expecting daytime storms to shut
down completely, but coverage should be isolated to scattered at
best.

Friday onward - high pressure forecast to shift to our north,
allowing for easterly flow and gradual moistening. Storm chances
return to typical monsoon levels.

&&

.AVIATION...For the 06Z package...A line of showers and
thunderstorms extending from Holbrook to Pinon are decreasing as
they move to the west-northwest. Light rain primarily west of I-17
and south of I-40 will continue into the early morning hours.
Scattered to numerous showers and a few thunderstorms will
develop again Monday after 18z-20z, with activity along the
Mogollon Rim extending from Flagstaff to the Grand Canyon and west
to the boarder. MVFR/IFR conditions in the stronger storms.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Expect above normal storm activity and high relative
humidity through Monday. Slightly drier and more stable conditions
arrive Tuesday, bringing activity back down to normal levels.

Wednesday through Friday...Chances for showers and thunderstorms
will continue, but coverage and frequency should decrease. Slightly
drier and warmer conditions near the surface will enhance the threat
for gusty outflow winds, associated with thunderstorms.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...Flash Flood Watch until midnight
MST tonight FOR AZZ004>018- 037>040.

&&

PUBLIC...TPS/DL
AVIATION...DB/TPS
FIRE WEATHER...Peterson

For Northern Arizona weather information visit
weather.gov/flagstaff

Hazardous Weather Outlook
National Weather Service Flagstaff AZ
950 AM MST Sun Jul 23 2017

AZZ004>018-037>040-240415-
Kaibab Plateau-Marble and Glen Canyons-Grand Canyon Country-
Coconino Plateau-Yavapai County Mountains-
Northeast Plateaus and Mesas Hwy 264 Northward-Chinle Valley-
Chuska Mountains and Defiance Plateau-
Little Colorado River Valley in Coconino County-
Little Colorado River Valley in Navajo County-
Little Colorado River Valley in Apache County-
Western Mogollon Rim-Eastern Mogollon Rim-White Mountains-
Northern Gila County-Yavapai County Valleys and Basins-
Oak Creek and Sycamore Canyons-Black Mesa Area-
Northeast Plateaus and Mesas South of Hwy 264-
950 AM MST Sun Jul 23 2017

This hazardous weather outlook is for Apache...Coconino...
Northern Gila...Navajo...and Yavapai Counties in Northern
Arizona.

.DAY ONE...Today and Tonight

Look for another round of scattered to numerous showers and
thunderstorms this afternoon and evening. The steering flow aloft
will be weak, pushing storms slowly toward the west-northwest. A
few storms today will be capable of dropping 1 to 3 inch downpours
which could result in flash flooding. A Flash Flood Watch has been
issued for all of northern and central Arizona.

Higher instability along and south of the Mogollon Rim could also
produce a few strong to severe thunderstorms, with hail up to one
inch in diameter and strong wind gusts.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Showers and thunderstorms are likely Monday, a few possibly
producing heavy rainfall and localized flash flooding. A decrease
in storm coverage is expected midweek before increasing again by
Thursday or Friday.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to standard operating procedures.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
1107 PM MST SUN JUL 23 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1102 PM     FLASH FLOOD      2 NNW BLACK CANYON CITY 34.09N 112.15W
07/23/2017                   YAVAPAI            AZ   TRAINED SPOTTER

            BLACK CANYON RIVER WASH IS 3'-4' DEEP OVER
            MAREN AVE. AND IS CURRENTLY IMPASSABLE. THE
            WATER CAME UP ABOUT 9:30 PM MST.

&&

DLB

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