Severe Thunderstorm Warning 21, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
904 AM MST Fri Jul 28 2023

.SYNOPSIS...The monsoon looks to ramp up over the coming days with
increasing chances for afternoon and evening showers and
thunderstorms. Hot conditions will continue across the region
through the first half of the weekend before finally starting to
cool down as monsoon activity increases.

&&

.UPDATE...As expected, with a favorable pattern in place, a large
thunderstorm complex developed over northwest Mexico. The result
is an ongoing surge of moisture into southern Arizona from the
Gulf of California. Yuma currently was carrying a 72 degree dew
point with southeast winds at 20 mph gusting to 30 mph during the
morning hours. Some of this moisture is sure to make it into
portions of southern Yavapai County by late this afternoon. The
flow today is more favorable for storms that develop over the
eastern Mogollon Rim and White Mountains to move west to
southwestward into the lower elevations. Gusty outflow from this
activity could collide with the Yavapai County moisture for a
better chance of severe thunderstorms and flash flooding late this
afternoon and into the evening. There is always a bit of
experiential guess work with these patterns but that is how we
see it this morning.

&&

.PREV DISCUSSION /252 AM MST/...Not much going on tonight in terms
of the weather across northern Arizona, besides for some light and
variable winds, near average temperatures, and some mid-level
clouds with more coverage towards the south. An impressive
mesoscale convective system (MCS) is currently impacting southern
portions of the Mexican state, Sonora, as another, much weaker
system continues to decay along the Arizona and Mexico border.

Another day of isolated to scattered shower and thunderstorm
activity is expected for this afternoon and evening with greatest
chances (40-50%) along and south of the Mogollon Rim and into the
White Mountains (60-70%). Hi-res guidance has storms beginning to
develop along the higher terrain by noon, increasing in coverage
thereafter. Leftover showers and storms persist through this
evening, with activity ending by 11 pm MST. Temperatures remain
hot across the region, peaking by noon just before clouds and
thunderstorms increase in coverage.

As we head into the weekend, the center of the high pressure
system (currently over the AZ/NM border) begins to shift eastward,
enhancing southerly flow into Arizona. This transition will allow
for an increase in moisture advection as dew points and PWATs
begin an upward trend across Arizona. As a result, POPs and shower
and thunderstorm coverage have increased for Saturday, with
widespread coverage forecast by Sunday. Temperatures look to
remain roughly 5-10 degrees above average for Saturday afternoon,
before beginning a cooling trend from Sunday onward.

Both the GEFS and the ECMWF Ens are in agreement with the high
shifting further to the east over Texas and Oklahoma for the first
half of next week. Scattered to widespread thunderstorm activity
is forecast for Monday and Tuesday with chances decreasing some on
Wednesday as PWATs begin a decreasing trend. As we wrap up next
week, ensemble guidance suggests a downturn in monsoonal activity
with a return of warmer temperatures. Confidence remains more low
to moderate at this time in regards to drier conditions for the
end of next week. The high does look to shift back westward and
position itself more directly over the Southwest, however,
depending on how much it does rain in the beginning of the week
and with no indications of any strong winds to scour out the
surface moisture, chances for precipitation are still on the
table.

&&

.AVIATION...For the 18Z TAF Package...Mainly VFR conditions expected
over the next 24 hours. Look for scattered showers and thunderstorms
through 03Z, mainly along/south of a KPGA-KINW-KRQE line with
isolated activity further north. Be on the lookout for wind gusts of
35 to 45 knots in the vicinity of storms. Aviation discussion not
updated for TAF amendments.

&&

.FIRE WEATHER...Today and Saturday...Scattered showers and
thunderstorms expected across northern Arizona each afternoon with
the best chances along and south of the Mogollon Rim through the
White Mountains. The primary threats will be lightning, erratic
outflow winds of 30 to 40 mph, and rainfall rates of 0.50-1.00" per
hour in any storms. Activity will gradually subside each evening.

Sunday through Tuesday...Scattered to widespread shower and
thunderstorm activity is expected each afternoon. Outside of any
outflow winds, expect west-southwest winds 10 to 20 mph each
afternoon. Daytime temperatures cooling through the period.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 8 PM MST Sunday for AZZ006.

&&

PUBLIC...McCollum/LaGuardia
AVIATION...McCollum/Meola
FIRE WEATHER...McCollum/Meola

For Northern Arizona weather information visit
weather.gov/flagstaff