489
FXUS65 KFGZ 111804
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
1104 AM MST Thu Jul 11 2024

.SYNOPSIS...Hot temperatures will continue through Friday, with a
slight cooling trend for the weekend. Moisture will slowly return
to the region, with chances for afternoon showers and thunderstorms
increasing each day, becoming widespread by the weekend and into
early next week.

&&

.UPDATE...Strong high pressure centered over northwestern Arizona
and southern Nevada continues to be the dominant feature in our
weather pattern. Anticyclonic flow around the high will keep a
northerly steering flow across Arizona. Moisture remains pooled
south of the Mogollon Rim across Yavapai and Gila counties, which
will be the area of focus for afternoon/evening storm development
today. Convective initiation should begin along the Mogollon Rim
and Coconino Plateau, with storms moving south and west into the
lower desert areas. Forecast surface based CAPE values of 500-1000
J/kg, along with about 20-30 kt of vertical wind shear, will
sustain a few strong to severe storms. With a dry boundary layer
still in place, strong wind gusts are the primary threat, though
hail cannot be ruled out.

&&

.PREV DISCUSSION /416 AM MST/...Tranquil weather conditions are
taking place across northern Arizona early this morning with
little to no wind and near average temperatures. High pressure
remains in place over the Great Basin and much of the Southwest
for today as it continues to migrate slowly towards the east. Hot
temperatures will persist to end the work week, 5-10 degrees above
average. Excessive Heat Warnings remain in effect for lower
valley/canyon locations below 4000 feet through this evening,
however, the end is in sight.

As the high pressure system gradually shifts eastward, southerly
flow returns allowing an increase in monsoonal moisture advection
from the south. Surface to mid-level moisture will continue to
increase slowly as a result with good agreement in ensemble
guidance suggesting a return to normal PWAT values for this time
of year (0.7-1.0") by this weekend.

As for this afternoon, both the HREF and HRRR guidances have
isolated shower and thunderstorm coverage developing after 1200
MST, continuing through this evening. Much of this afternoon`s
development will be confined to locations south of the Mogollon
Rim, with greatest chances (25-55%) near Prescott, Payson, and the
White Mountains region. Surface moisture should still be lacking
this afternoon with widespread minimum humidity of 5-15%. Multiple
model soundings from across northern Arizona all show the
"inverted-V" signature from the surface up to 400-500 mb,
suggesting that any thunderstorms that do form should be high-
based. This means that the main threats from storms this afternoon
will likely be the potential for dry lightning, gusty outflow
winds, and hail. Given that surface winds are forecast to be
primarily from the north today, showers and storms should move
southward, 10-20 mph.

POPs and thunderstorm coverage increases on Friday, becoming
widespread for Saturday and Sunday. Activity will likely follow
the diurnal pattern each day, with storms developing in the early
afternoon over the high terrain, then spreading across northern
Arizona through the afternoon and into the evening. Temperatures
on Friday are forecast to remain above average, with an Excessive
Heat Warning continuing for the Grand Canyon and up to Page,
cooling and returning to normal for this weekend across the
region. With monsoonal moisture likely to become abundant for this
weekend as dewpoints rise to the 50s-60s range, any storms should
produce a sufficient amount of rainfall (>0.10"), reducing the
threat of dry lightning and new fire starts.

With good model agreement in regards to the high pressure system
centered over the Four Corners region for Sunday into Monday,
another widespread activity day is forecast for Monday afternoon.
As we head into the middle of next week, long range models suggest
a shift in storm coverage towards the east with greater chances
favoring locations along and east of the Mogollon Rim. Since
confidence is on the lower side at this time, POPs and QPF have
been reduced for much of next week after Monday as the current
NBM guidance is a bit high and not quite in line with the GEFS
and EPS. However, a persistent drying out and warming period,
like the one we have been experiencing this last week, does not
look likely for next week at this time.

&&

.AVIATION...Thursday 11/18Z through Friday 12/18Z...Isolated to
scattered showers and thunderstorms today southwest of a KFLG -
KRQE line. Best chances will favor KPRC/KSEZ terminals later this
afternoon. Strong wind gusts 40-50 kts, hail, and brief heavy
rain possible with stronger storms. Outside of storms, look for
winds 5-15 kts varying in direction.

OUTLOOK...Friday 12/18Z through Sunday 14/18Z...Scattered
showers/storms from KGCN - KRQE southward on Fri, increasing in
coverage and spreading across all of northern AZ on Sat. Brief
MVFR possible in stronger storms with otherwise VFR conditions.
Outside of thunderstorms, expect prevailing winds generally 10 kts
or less.

&&

.FIRE WEATHER...Today and Friday...Hot temperatures continue
today, with slightly cooler temperatures on Friday. 20-40% chance
of showers/thunderstorms across Yavapai County today, and 30-60%
chance across the Rim and White Mountains. Look for increasing
coverage for showers/storms on Friday. Expect winds 15 mph or less
and varying in direction both afternoons outside of gusty/erratic
outflow winds.

Saturday through Monday...Seasonable temperatures return along with
scattered to widespread showers/thunderstorms. A mixture of wetting
rains, small hail, gusty winds, and lightning will be possible each
afternoon/evening. Outside of storm driven winds, expect generally
west through southwest winds 5-15 mph.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 8 PM MST /9 PM MDT/ Friday for
AZZ005-006.

Excessive Heat Warning until 8 PM MST this evening for AZZ037.

&&

$$

PUBLIC...MCT/LaGuardia
AVIATION...MCT
FIRE WEATHER...Konieczny

For Northern Arizona weather information visit
weather.gov/flagstaff