Flash Flood Warning 48, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
846 AM MST Wed Aug 23 2023

.SYNOPSIS...Daily showers and thunderstorms are expected into
next week. The wettest days will be today and Thursday, when the
remnants of Tropical Depression Harold bring more widespread
activity. Temperatures will remain cool through Thursday,
returning closer to average over the weekend.

&&

.UPDATE...Monsoon moisture remains in place across northern
Arizona with another round of showers and thunderstorms today.
Activity will be enhanced later this afternoon and likely
continue through the night as a result of the weak remnants of
tropical storm Harold. Stronger storms will produce extremely
heavy rain with areas of localized flooding likely. Consider this
when you are out and about driving around today.

&&

.PREV DISCUSSION /225 AM MST/...Today...A strong ridge remains
over the central US, allowing for Tropical Depression Harold to
cut under the ridge and moves into the southwest. With ample
moisture in place, PWATs should range from about 0.90 inches over
the high terrain to 1.25 inches below the Mogollon Rim. The
combination of the moisture and added synoptic-scale dynamics
from the remnants of Harold, will help to promote the development
of showers and storms today, and especially into the overnight.

Scattered to widespread showers and thunderstorms are expected to
develop by the afternoon and evening hours. Storms look to develop
initially over the higher terrain, then increasing in coverage
over much of northern and central Arizona once the better
dynamics move in during the evening and early overnight hours.
HREF PMM guidance show the greatest risk for heavy rainfall will
mainly be from the Kaibab Plateau southeastward through the
Mogollon Rim. Storm motions should be around 10 kts, so residency
time should be enough to create a flash flood threat, especially
over flood sensitive areas. Any training storms will also add to
the threat of flash flooding. SBCAPE looks to be about 500-1000
J/Kg and deep-layer shear around 15-25 kts, so overall the risk
of severe weather remains low. The greatest risk, looks to be
near the Kaibab Plateau during the afternoon.

Thursday...The center of the circulation moves over Arizona
Thursday morning, which should keep showers and storms around
through the morning. More widespread activity then returns during
the afternoon, especially north of the Mogollon Rim. The flash
flood threat looks to also shift northward, with the HREF hitting
on areas of Coconino County and the Navajo Nation being at the
greatest risk. Showers storm motions on Thursday may also help to
promote a flash flood threat.

Friday through Tuesday...The ridge over the central US begins to
degrade and retrograde to a position that more closely resembles a
typical monsoonal circulation. Thus, daily chances for showers and
thunderstorms are expected to continue through the end of this
week and into next week. Daily coverage will largely be
determined by the strength and location of the high pressure
center, as it wobbles around the southwest.

&&

.AVIATION...For the 18Z TAF Package...Mainly VFR conditions are
forecast through the TAF period outside of showers and
thunderstorms. Expect scattered showers and thunderstorms to become
more widespread after 22Z. Activity will diminish after 04Z
Thursday, but low cloud ceilings may linger over the Mogollon Rim
into the morning. Some storms will produce heavy rain, small hail,
frequent lightning, and gusty, erratic winds in excess of 30 knots.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Today and Thursday...Scattered to widespread
showers and thunderstorms expected both days. Gusty, erratic winds
gusts between 35 to 45 mph in the vicinity of stronger storms.
Mainly southeast winds between 10 to 20 mph through this afternoon,
becoming south to southwest between 5 to 15 mph on Thursday.

Friday through Sunday...Monsoon activity will continue, becoming
more scattered through the weekend. Warming temperatures will rise to
near average by Saturday. Southwesterly winds around 15 mph or less
each day.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...None.

&&

PUBLIC...McCollum/Humphreys
AVIATION...Benji/Meola
FIRE WEATHER...Benji/Meola

For Northern Arizona weather information visit
weather.gov/flagstaff

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