Special Weather Statement, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
322 PM MST Thu Jul 29 2021

.SYNOPSIS...Abundant monsoonal moisture will persist over
northern Arizona through the weekend. The greatest thunderstorm
coverage is expected through Friday, with storms capable of
producing high rain rates and flash flooding. Thunderstorm
coverage decreases Saturday and Sunday with even less activity to
begin next week.

&&

.DISCUSSION...

*Issued a Flash Flood Watch for portions of Coconino County from
 early Friday afternoon through late Friday evening.

Widespread shower and thunderstorm activity is taking place this
afternoon with greatest coverage across Navajo and Apache counties
as well as Yavapai County. Expect coverage to spread across much
of northern Arizona within the next hour or so. Activity is
forecast to decrease later this evening, however overnight showers
and isolated thunderstorm chances are possible across Yavapai and
western Coconino counties.

As the high pressure ridge amplifies over the western half of the
country, monsoonal moisture advection increases and extends north
and westward into portions of Nevada, Utah, Colorado, and eastern
California. With PWAT values remaining in the 1.0-1.2 inch range
across Arizona, sufficient forcing, and short range model
guidance suggesting widespread thunderstorm coverage... we went
ahead and issued a Flash Flood Watch for portions of Coconino
County for Friday afternoon/evening. Widespread flash flooding is
likely in this area during this time with 1-2 inch per hour
rainfall rates expected.

With most activity anticipated west of I-17 and Hwy 89 on Friday,
Yavapai County could also see some high rainfall rates from
storms. However, we have decided to leave this area out of the
Watch at this time due to a few reasons. Hi-res guidance continues
to suggest that Coconino County will see the most coverage on
Friday with the highest potential for widespread flash flooding.
We are also less confident in Yavapai seeing widespread flooding
because of the anticipated nocturnal activity likely to take place
in the area tonight. This scenario could result in leftover
debris cloud cover overnight into Friday morning which could limit
the overall convection during the day. Flash flooding is
possible, but not looking widespread at this time.

Thunderstorm coverage looks to begin a downward trend from
Saturday onward as the high pressure ridge transitions directly
overhead northern Arizona. Less forcing and monsoonal moisture are
likely in this pattern with warming temperatures forecast.

&&

.AVIATION...For the 00Z package...Mainly VFR conditions expected.
Thunderstorm activity continues with brief periods of MVFR
conditions and gusty and erratic winds in and around thunderstorms.
Scattered shower and thunderstorm coverage is then expected to
decrease after 06Z Friday. Another round of widespread thunderstorms
is anticipated for Friday. Aviation discussion not updated for
TAF amendments.

&&

.FIRE WEATHER...Scattered to widespread thunderstorm coverage is
expected to continue for the remainder of today with another round
on Friday with flash flooding and lightning being the primary hazards.
Rainfall rates of 1 to 2 inches per hour is possible. Lesser coverage
anticipated for Saturday. Light winds are forecast outside of
thunderstorm activity.

Sunday through Tuesday...Isolated to scattered storms are forecast for
Sunday with even lesser activity for Monday and Tuesday. Temperatures are
likely to begin a warming trend during this time.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...Flash Flood Watch from Friday afternoon through Friday evening
FOR AZZ004>007-012-015.

&&

PUBLIC...LaGuardia
AVIATION...LaGuardia
FIRE WEATHER...LaGuardia

For Northern Arizona weather information visit
weather.gov/flagstaff

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
1242 PM MST THU JUL 29 2021

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

1238 PM     HAIL             1 WSW PARKS             35.26N 111.96W
07/29/2021  E0.75 INCH       COCONINO           AZ   TRAINED SPOTTER

&&

TM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
330 PM MST THU JUL 29 2021

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

0329 PM     FLASH FLOOD      1 WNW CORNFIELDS        35.66N 109.70W
07/29/2021                   APACHE             AZ   PUBLIC

            SOCIAL MEDIA REPORT OF FLOODING OVER ROUTE
            15 AT MILE POST 86.

&&

TM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
351 PM MST THU JUL 29 2021

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

0341 PM     FLASH FLOOD      2 WSW CORNFIELDS        35.65N 109.72W
07/29/2021                   APACHE             AZ   PUBLIC

            CORNFIELDS CHAPTER REPORTED FIVE AREAS ALONG
            ROUTE 15 FROM BURNSIDE TO GREASEWOOD AZ THAT
            ARE FLASH FLOODING WITH MORE THAN ONE TO TWO
            FEET OF WATER. HEAVY DEBRIS AND THICK MUD
            WASHED ACROSS THE ROAD.

&&

DB

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
435 PM MST THU JUL 29 2021

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

0337 PM     FLASH FLOOD      14 S CIBECUE            33.83N 110.46W
07/29/2021                   GILA               AZ   DEPT OF HIGHWAYS

            ROAD CLOSURE DUE TO FLOODING.

&&

Special Weather Statement
National Weather Service Flagstaff AZ
505 PM MST Thu Jul 29 2021

AZZ007-012-015-016-038-300045-
Little Colorado River Valley in Coconino County-Western Mogollon
Rim-Coconino Plateau-Oak Creek and Sycamore Canyons-Eastern Mogollon
Rim-
505 PM MST Thu Jul 29 2021

...SIGNIFICANT WEATHER ADVISORY FOR THE FLAGSTAFF AREA IN COCONINO
COUNTY UNTIL 545 PM MST/645 PM MDT/...

At 503 PM MST/603 PM MDT/, Doppler radar was tracking strong
thunderstorms along a line extending from 12 miles west of Gray
Mountain to 7 miles southeast of Mormon Lake. Movement was southwest
at 25 mph.

Wind gusts up to 50 mph will be possible with these storms.

Locations impacted include...
Flagstaff, Sunset Crater Volcano National Monument, Timberline,
Kachina Village, Valle, Winona, Mormon Lake, Doney Park, Fort
Valley, Bellemont, Munds Park, Walnut Canyon National Monument,
Mountainaire, and Wupatki Trails.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 3565 11218 3577 11162 3495 11131 3493 11168
      3506 11182 3502 11185 3510 11192
TIME...MOT...LOC 0003Z 065DEG 22KT 3568 11168 3486 11136

Special Weather Statement
National Weather Service Flagstaff AZ
535 PM MST Thu Jul 29 2021

AZZ037-300100-
Yavapai County Valleys and Basins-
535 PM MST Thu Jul 29 2021

...SIGNIFICANT WEATHER ADVISORY NEAR CONGRESS IN YAVAPAI COUNTY
UNTIL 600 PM MST...

At 534 PM MST, Doppler radar was tracking a strong thunderstorm near
Congress, or 9 miles north of Wickenburg. This storm was nearly
stationary.

Half inch hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Congress.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 3420 11270 3402 11269 3402 11290 3418 11291
TIME...MOT...LOC 0034Z 079DEG 2KT 3410 11280