Flash Flood Warning 239, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
108 PM MST Thu Aug 18 2022

.SYNOPSIS...An active monsoon pattern will continue across
northern and central Arizona through the remainder of the week.
Heavy rainfall leading to flash flooding will continue to remain a
threat, especially through Saturday. Cooler temperatures are
expected through the weekend.

&&

.DISCUSSION...Satellite imagery reveals maturing cumulus clouds across
the north rim of the Grand Canyon, the SF Volcanic Field, and
Black Mesa. Forecast instability values from the HREF suggest
around a 50% chance of Boundary Layer CAPE values in excess of 500
J/kg along and west of the Mogollon Rim. With around a 30% of
CAPE at or above 1000 J/kg across western and southern Yavapai
County. Several HREF members as well as the Univ of AZ WRF suggest
that that a loosely organized complex will slide off the Mogollon
Rim and advance west and southward. Given that 24 hour radar-
based QPE from across Yavapai and portions of Oak Creek/Sycamore
Canyons runs between 1-2 inches with isolated 3" amounts, a Flash
Flood Watch appears prudent. The Flash Flood Watch for the
aforementioned areas will run from 1400 MST thru 2300 MST. In
addition, given the high likelihood of a hot and well-mixed PBL
across the Yavapai County deserts, there will be a strong to
damaging wind threat (50-60 mph) especially if the convection can
consolidate along a fortified cold pool. There's a little
uncertainty regarding exactly where this complex will take shape
as some guidance has the most vigorous convection/highest QPF
along the Yavapai/Mohave county border while other solutions
suggest the main show will be across Yavapai/Gila/Maricopa county
interface. Regardless, PoPs and QPF have been increased across
this area to account for the increased flash flood, and damaging
wind potential.

Tonight, convection will persist as many of the CAMs imply the
development of a mesoscale convective vortex or MCV. With this MCV
appearing probable to develop across Yavapai County, it'll induce
moist nocturnal upslope flow for areas near and east of the
I-17/US HWY 89 corridors. We'll hold onto 60-80% PoPs through the
pre-dawn hours on Friday and the current Flash Flood Watch that
runs through tonight appears very reasonable.

Friday will have the potential to produce significant flash
flooding across northern Arizona. Extraordinary PWAT values near
1" along the Mogollon Rim will support very efficient warm rain
processes and given the antecedent conditions (many areas
exceeding 150% of normal across the High Country), flash flooding
seems nearly a guarantee...especially for fire scars, poor
drainage areas, and normally dry washes (which are likely already
running high with water). Be sure to avoid areas prone to rapid
flash flooding such as low water crossings and slot canyons. If
you do decide to recreate, be sure that you have multiple ways to
receive warning information!

Saturday...monsoon activity will remain scattered to numerous for
most of northern Arizona for the first half of the weekend.
Although models are favoring a day less active than Friday,
flooding and flash flooding will remain a major weather threat.

Sunday onward...our synoptic scale pattern will begin to shift to
a less intense monsoon set-up for most of northern Arizona. Due
to multiple factors (inverted trough over Mexico, trough pushing
westward from the East Coast, ridging over northwest Arizona, and
a trough forming over the Great Basin), we'll begin to see a
northeastern flow aloft. This wind flow will funnel in drier air
to the northern portion of our CWA, but areas along and south of
the Mogollon Rim still have the potential to see isolated to
widespread thunderstorm activity well into next week. We'll have
more updates on the potential decrease in monsoon activity as we
approach the end of the weekend.

&&

.AVIATION...For the 00 UTC TAF package...SHRA/TSRA will likely be
in progress at the start of the 00 UTC TAF cycle, especially at
PRC and SEZ. The potential for MVFR/IFR vsby as well as
gusty/erratic winds will increase within TSRA cores. Strong TSRA
winds are most likely at PRC with gusts up to 30-40 knots.
Nocturnal SHRA/TSRA is advertised at all sites with activity
dwindling from west to east through the pre-dawn hours on Friday.
Another round of widespread SHRA/TSRA should be anticipated at
just about all TAF sites Friday afternoon with a lower chance
(closer to 30% at PRC).

&&

.FIRE WEATHER...Showers and thunderstorms have quickly ramped up this
afternoon across northern Arizona and will continue throughout
the evening hours. An uptick in storm activity is forecast Friday
and Saturday area wide. Gusty erratic winds and localized flash
flooding will be likely.

Sunday through Tuesday...A downward trend in thunderstorms is
forecast to start Sunday and continue through the early part of
next week. Isolated to scattered storm coverage is still expected.
Localized flash flooding will still be possible each day.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Friday evening for AZZ004>006-104>106.

Flood Watch through Saturday evening for AZZ007-015-107-115.

Flood Watch until 11 PM MST this evening for AZZ008-037-038-108-
137-138.

Flood Watch from Friday morning through Saturday evening for
AZZ008-011>014-016>018-037-038-040-108-111>114-116>118-137-138-
140.

&&

PUBLIC...Swenson/Bain
AVIATION...Bain
FIRE WEATHER...Swenson

For Northern Arizona weather information visit
weather.gov/flagstaff

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

Special Weather Statement
National Weather Service Flagstaff AZ
201 PM MST Thu Aug 18 2022

AZZ008-037-182130-
Yavapai County Valleys and Basins-Yavapai County  Mountains-
201 PM MST Thu Aug 18 2022

...A strong thunderstorm will impact portions of Yavapai County
through 230 PM MST...

At 200 PM MST, Doppler radar was tracking a strong thunderstorm 7
miles east of Rimrock, or 15 miles east of Camp Verde. This storm was
nearly stationary.

HAZARD...Winds in excess of 30 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Wet Beaver Creek Campground and V Bar V Visitors Center.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Heavy rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3474 11156 3458 11156 3456 11170 3471 11172
TIME...MOT...LOC 2100Z 068DEG 3KT 3464 11161

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...30 MPH

MAS