Severe Thunderstorm Warning 156, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
1011 AM MST Thu Aug 23 2018

.SYNOPSIS...Deep monsoon moisture will remain over northern
Arizona through Friday. This will result in good chances for
afternoon and evening thunderstorms each day. A downturn in shower
and thunderstorm activity is possible over the weekend and
especially early next week.

&&

.DISCUSSION...An active monsoon day is on tap for northern
Arizona. Much of the area is enjoying partly to mostly sunny skies
this morning. Scattered to numerous thunderstorms are expected to
develop late this morning and continue into the afternoon hours
with ample moisture in place. General storm motion will be from
west to east. Some wind shear will be present today so stronger
storms with hail and gusty winds are possible. The primary threat
will be flash flooding especially in areas that have received
significant rainfall over the past few days including western
Coconino County and south into Yavapai County.

Current forecast looks good and no updates are needed this
morning.

&&

.PREV DISCUSSION /418 AM MST/...Deep moisture remain over all of
Arizona this morning. Satellite derived PW shows one to two inches
along the Colorado River from Yuma to the Four Corners. Cloud
cover extends along and south of a Prescott-Winslow-Four Corners
line this morning. Showers and thunderstorms are still ongoing
over southern Arizona this morning.

A trough of low pressure moving through the Great Basin today will
cause the winds aloft (above 18 kft/500 mb) to shift and become
more southwesterly today over northwestern Arizona. This will help
some storms become stronger today and move faster...roughly from a
Prescott-Four Corners line today. Moisture values will change
little today so scattered/numerous thunderstorms are expected
today and Friday.

A stronger southwest flow develops over the weekend for a
downward trend in moisture and thunderstorm activity over northern
Arizona. This downward trend could last well into next week.

&&

.AVIATION...For the 18Z package...Sct-nmrs shra/tsra and isold +tsra
by 18Z-19Z. Most active areas along and west of a KPGA-KGCN-FLG-KSOW
line. Brief MVFR/IFR in the strongest cells. Light winds, except for
thunderstorm outflows. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Monsoon moisture will remain over the district
with good chances for showers and thunderstorms again today and
Friday. Overnight activity is possible.

Saturday through Monday...A drier air mass will slowly filter
southward from the UT/AZ border starting Saturday. The drier air
will lead to a downturn in shower and thunderstorm activity for
areas north and east of the Mogollon Rim by Monday. The White
Mountain region can still expect high chances for showers and
thunderstorms.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...NONE.

&&

PUBLIC...TPS/KD/MAS
AVIATION...Peterson
FIRE WEATHER...Peterson/KD

For Northern Arizona weather information visit
weather.gov/flagstaff

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
1158 AM MST THU AUG 23 2018

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

0817 PM     FLASH FLOOD      1 SW YARNELL            34.22N 112.75W
08/22/2018                   YAVAPAI            AZ   DEPT OF HIGHWAYS

            THIS IS A POST-EVENT REPORT. ARIZONA DEPT.
            OF TRANSPORTATION REPORTS SR 89 IS CLOSED IN
            BOTH DIRECTIONS FROM FLOODING AT MILE POST
            277.4 (ABOUT 9 MILES NORTH OF SR 71).

&&

MCT