991
FXUS65 KFGZ 161523
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
823 AM MST Mon Sep 16 2024

.SYNOPSIS...Gusty winds area wide, and chances for showers and
thunderstorms across the eastern half of the state will continue
through tonight. Mostly dry, cool, and breezy weather then returns
on Tuesday through much of the week.

&&

.UPDATE...A sharp dividing line between a very dry air mass and
deeper moisture lies near the I-17/US89 corridor at 8 AM. Surface
dewpoints to the east of this line are in the 50s and low 60s,
while west of the line readings in the 20s and 30s are common.
Showers and a few thunderstorms continued overnight southeast of a
Payson to Window Rock line, with some moderate rainfall amounts
measured in the White Mtns region (just over 0.50" in Pinetop-
Lakeside to nearly an inch on the southern slopes of the
mountains). We`re in a lull of activity currently, but with the
approach of the upper low and some meager daytime heating we
expect some additional shower and thunderstorm development east of
the I-17/US89 corridor later this morning through early evening,
then confined mainly east of Payson-Window Rock overnight through
around sunrise Tuesday. The other story today in the gusty
southwest winds, expected to gust 40-50 mph for much of northern
Arizona. A Wind Advisory goes into effect at 10 AM MST and
continues through 7 PM.

&&

.PREV DISCUSSION /450 AM MST/...Today...A trough sits over
northern California and will gradually rotate it`s way through
the Great Basin today. While upper-level dynamics will increase
with the trough, the anticipated moisture surge has been fairly
underwhelming, with moisture largely limited to the eastern
portions of the state.

For most everywhere else, the main impacts from this system will be
gusty southwest winds this afternoon. Gusty winds of 35-45 kts
look likely across much of the higher terrain, especially where
deeper mixing occurs. Areas downwind of the Mogollon Rim into the
Little Colorado River Valley could see strong gusts upwards of
45-50 kts. Guidance does suggest that winds could remain somewhat
elevated overnight, especially downwind of the terrain, however
to what extent remains uncertain as soundings suggest that most
locations should decouple overnight.

Currently, storms have fired over southeastern Arizona, and should
continue to move northeastward and increase in coverage. Latest hi-
res guidance continues to keep most of the activity over Navajo and
Apache counties, with some isolated activity potentially making it as
far west as the I-17/US-89 corridor. A couple of strong to maybe
severe storms can`t be fully ruled out, but widespread severe
weather is not anticipated. Additionally, given storm motions of
around 30-40 kts and PWATs of 0.80-1.00 inches, widespread flash
flooding is not anticipated. The only exception would be areas of
training storms or any very flood sensitive areas

Tuesday and Wednesday...Drier, and colder air sets in for Tuesday
with afternoon high temperatures nearly 10 degrees below normal for
this time of year. The coldest temperatures look to occur overnight
Tuesday into Wednesday morning, with some much of the High Country
dipping into the 30s F and even into the upper 20s F in the
typically colder locations.

A couple of isolated showers can`t be fully ruled out early in the
day as the last of the moisture and upward motion moves out of
Arizona. Otherwise, the vast majority of the area will remain dry
and breezy through Wednesday.

Thursday through Sunday...Unsettled weather continues into the end
of the week as another trough digs southward along the California
Coast on Thursday. As the trough ejects off the Pacific, it moves
across the lower Great Basin, keeping the system fairly moisture
starved. As a result, mainly isolated coverage of showers are
expected. However, there is a slight signal towards an attempt to
advect some moisture northward from the Gulf, but this looks
limited. Dry conditions look to return for the weekend as the trough
moves into eastward.

Temperatures will continue to be cool through much of the period
with the influence of the trough, along with breezy winds. After the
trough, temperatures look to try to rebound with near-normal
afternoon highs by the afternoon.

&&

.AVIATION...Monday 16/12Z through Tuesday 17/12Z...Isolated to
scattered SHRA/TSRA are forecast to persist east of a KPAN-KFLG-
KOV7 line through the period. MVFR conditions and hail are
possible with the stronger storms. Outside of storms, expect
southwest winds 5-15 kts until 15Z, increasing to southwest at 15-25
kts with gusts 30-40 kts. Wind speeds decreasing after 02Z.


OUTLOOK...Tuesday 17/12Z through Thursday 19/12Z...Storms
decrease to isolated coverage after 06Z Tuesday with dry
conditions area-wide after 18Z Tuesday. Southwest winds 15-25 kts
gusting 25-35 kts Tuesday, decreasing to southwest at 10-20 kts
gusting 20-30 kts on Wednesday.

&&

.FIRE WEATHER...Today through Tuesday...Scattered showers and
thunderstorms are in the forecast through Tuesday morning, mainly
east of a Payson to Page line. Drier weather will arrive later on
Tuesday. South to southwest winds at 15 to 25 mph with gusts of 30
to 45 mph will develop by this afternoon, decreasing to 10 to 20 mph
with gusts of 25 to 35 mph on Tuesday. Daytime temperatures cooling
by 5 to 10 degrees compared to the weekend.

Wednesday through Friday...Remaining cool, breezy and mostly dry.
Another low pressure system could bring a few showers to northwest
Arizona on Thursday. Look for southwest winds at 10 to 20 mph
gusting 30 mph on Wednesday and Thursday, then becoming west to
northwest at 10 to 20 mph for Friday.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 7 PM MST /8 PM MDT/ this evening for
AZZ004>009-012-013-015-016-038>040.

&&

$$

PUBLIC...JJ/Humphreys
AVIATION...McCollum
FIRE WEATHER...McCollum

For Northern Arizona weather information visit
weather.gov/flagstaff