977
FXUS65 KFGZ 202330
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
430 PM MST Sat Jul 20 2024

.SYNOPSIS...Scattered showers and thunderstorms are expected each
day through next week. Temperatures will remain a bit above average
through the weekend, with light winds.

&&

.DISCUSSION...High pressure aloft was slowly meandering northward
to over Nevada and Utah Saturday afternoon. The high will then
become stationed over Nevada/Utah through the middle of next week
allowing moisture from the Gulf of California and thunderstorm
outflow from over northwest Mexico and southern Arizona to move
northward.

For today and this evening...Not much change. Generally isolated
showers and thunderstorms mostly dying off during the evening
hours. There will remain slight chances for a stray shower or
thunderstorm through the night as remnant thunderstorm outflow
boundaries cross the area and potentially fire off additional
storms.

From Sunday into Wednesday...The high takes position over Nevada
and Utah which is a known severe thunderstorm and flash flood
producing pattern for central and southern Arizona. Why? The
position of the high allows for a persistent flow of low-level
moisture from over the Gulf of California toward a surface based
thermal low. In addition, thunderstorm activity over northwest
Mexico usually increases under this pattern providing pushes of
moisture via thunderstorm outflow. The result, low-level moisture
tends to bank against the Mogollon Rim. In the mid- to upper-
levels, northeast flow around the high tends to clear things out
each night for maximum heating and development of instability
during the morning hours. Storms that build from the Grand Canyon,
across the Mogollon Rim into the White Mountains then are pushed
southward into the moist/unstable air mass to the south guided by
the northeast flow. There will be an increased threat for severe
thunderstorms and heavy rain over central Arizona over the next
few days. Under this pattern moisture tends to struggle to move
further north than the Mogollon Rim under the influence of that
same dry northeast flow aloft. The result, enough monsoon moisture
will remain for an isolated storm threat across northeast Arizona
but the main action will likely be over central and southern
portions of the state over the next few days.

Heading into Thursday and the end of next week...A trough moving
across the Pacific Northwest will suppress the Nevada/Utah high
southward. It looks like enough monsoon moisture will remain for
daily showers and thunderstorms but with the best chances
gradually pushing southward and eastward as a drier air mass moves
in from over the Eastern Pacific. High temperatures are apt to
climb higher during this period.

&&

.AVIATION...Sunday 21/00Z through Monday 22/00Z...Mainly VFR
conditions are expected through the period with SCT-BKN cloud
cover near 10,000 feet AGL. Scattered -SHRA/-TSRA with brief
periods of MVFR VIS are likely through 03Z, diminishing
thereafter. Clearing sky cover overnight before another round of
showers and storms begins to develop by 19Z over the high terrain.
Outside of gusty, up to 30 kts, and erratic outflows from storms,
anticipate light and variable winds overnight, becoming north 5-15
kts by 20Z.

OUTLOOK...Monday 22/00Z through Wednesday 24/00Z...Scattered
showers and thunderstorms are forecast from 19Z-03Z each day with
greatest coverage along and south of a KGCN-KFLG-KSOW line. Expect
mainly VFR conditions during this time with brief periods of MVFR
conditions in stronger storms. North to west winds, 5-15 kts, are
forecast each afternoon, besides for gusty and erratic outflow
winds from any showers/storms.

&&

.FIRE WEATHER...Sunday and Monday...Look for mainly afternoon and
evening showers/thunderstorms. Outside of gusty/erratic thunderstorm
outflow expect light winds at 5 to 15 mph. Little change in the
forecast high and low temperatures but minimum RH values of 10-20%
on Saturday will climb to 20-30% by Monday as monsoon moisture
increases.

Tuesday through Thursday...The chance for afternoon and evening
showers/thunderstorms will continue. As always, look for gusty and
erratic winds in the vicinity of storms. Otherwise, light winds at 5
to 15 mph. Turning a bit warmer with afternoon RH values ranging
from 20-30%.

&&

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

&&

$$

PUBLIC...McCollum
AVIATION...LaGuardia
FIRE WEATHER...Konieczny

For Northern Arizona weather information visit
weather.gov/flagstaff