Flash Flood Warning 197, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
152 AM MST Sun Aug 14 2022

.SYNOPSIS...The active monsoon pattern will continue across
the Arizona High Country over the next 5 to 7 days. The main
hazards associated with activity will be heavy rain and flash
flooding. As a reminder, be sure to avoid flood prone areas. If
you come across flooded roadways...make the smart choice and turn
around, don't drown.

&&

.DISCUSSION...Saturday afternoon convection continues to dwindle
as of 1 AM. An outflow boundary continues to race toward the
northwest from decaying showers/storms along the Valley Floor
and there's around a 15-20% chance that a few showers erupt along
the leading edge through sunrise this morning. Otherwise, expect
partly cloudy skies. For areas that clear...some patchy fog will
become a possibility, with a greater probability of fog if these
cloud-free areas received rainfall recently.

Widespread mid/upper level cloudiness is on tap for today which
should translate to a slow increase in the coverage of showers
and thunderstorms. The latest NWP suggests that a MCV from the
aforementioned convection farther south may drift toward the
northwest through the day today. This may instigate a moist
upslope flow from areas across the AZ Strip...down to the Mogollon
Rim and into the White Mountains. 00 UTC HREF Probability of
Exceeding (POE) 1" of rainfall ranges between 50 and 70% along
these areas. Given that PWATs will climb to or just over 1"
(nearly 100% probabilities) and the subsequent efficient warm-rain
processes likely to ensure in mature convection, we'll go ahead
and issue a Flood Watch for Flash Flooding for portions of the
High Country today and into the early portion of tonight. Note,
not all areas in the watch will experience heavy rain/flash
flooding as the coverage of storms won't be 100%.

While the consensus of hi-res NWP doesn't support widespread
heavy rain after about midnight Monday morning, random nocturnal
outflow collisions will mean that convection could persist into
the pre- dawn hours on Monday morning. Several HREF members along
with some of the coarser deterministic NWP supports at least a
40-50 PoP during this time period.

As one can expect, Monday's rain/storm chances are somewhat
predicated on the coverage of this afternoon's activity. For now,
PoPs will mirror the multi-model consensus which places 70-80%
rain/storm chances across the White Mountains and Mogollon Rim.
The tail-end of the HREF, however, suggests that we may be able to
shift the greatest PoPs to areas near/west of the I-17 and US HWY
180 corridors (basically Yavapai and western Coconino). It's quite
possible that we'll need another Flood Watch for Flash Flooding
for these areas, as some of the HREF POE 3" across parts of
Yavapai and Coconino counties is actually around 40%.

For the extended forecast, there's not a ton in ensemble guidance
that suggests much of a break from daily shower and thunderstorm
chances. As such, NBM PoPs appear reasonable. Wednesday may offer
slightly lower rain chances (only around 40-60% chances), but rain
chances ramp back up as additional low level moisture surged
northward from Mexico. Flash Flooding will remain the primary
hazard given antecedent conditions and favorable precipitable
water (indicative of warm rain processes).

&&

AVIATION...For the 12Z TAF package...ISO SHRA and TSRA early this
morning with coverage increasing by 19Z, becoming widespread through
the afternoon into the early evening. Peak activity will be along a
KGCN-KFLG-KPAN-KJTC line. Heavy rain will cause periods of MVFR/IFR
with gusty winds near storms. Expect VFR conditions and light
surface winds away from storms. Aviation discussion not updated for
TAF amendments.

&&

FIRE WEATHER...Widespread showers and storms today and Monday with
peak activity each afternoon. Light winds will be interrupted by
gusty, erratic winds near storms. Localized flash flooding remains a
threat.

Tuesday through Thursday...Minimal change through the week. Monsoon
moisture will remain in place with showers and thunderstorm each day.

&&

&&

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

&&

PUBLIC...Bain
AVIATION...JM
FIRE WEATHER...JM

For Northern Arizona weather information visit
weather.gov/flagstaff