833
FXUS65 KFGZ 201755
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
1055 AM MST Fri Sep 20 2024

.SYNOPSIS...A low pressure system will bring cooler temperatures,
gusty winds, and chances for showers and thunderstorms tonight
through Saturday. Warmer and drier weather is expected to return for
much of the upcoming week.

&&

.UPDATE...Partly cloudy skies are being observed across northern
Arizona this morning in response to the approaching upper level
low over southern California. The low will slowly approach Arizona
today with another mild and breezy day in store. Most
precipitation chances will hold off until after dark, with the
exception of a few isolated showers or storms across far western
Coconino/Yavapai counties. The forecast is in line with the latest
high-resolution model guidance this morning and only minor
updates were made to the cloud cover this morning.

&&

.PREV DISCUSSION /533 AM MST/...An upper level low pressure system
continues to spin across southern California early this morning.
As we move through the day the low will start to track to the east
to northeast and will cross through Arizona tonight through
Saturday. Models continue to support precipitation, mainly along
and north of a Prescott to Window Rock line. The low is not moving
particularly fast as it is cut off in both the mid and upper
levels. The slow movement of the low will mean the precipitation
will linger into Saturday, likely ending during the afternoon. It
is still looking like a meager event with most areas seeing less
than 0.25" of rain. There is some instability available along with
some shear so thunderstorms are possible as the low makes its way
across the region. However, the best shear/instability is offset
from the onset of the precipitation and while there may be a few
stronger storms that develop, it is not looking like we will see
much in the way of strong/severe storms and any that do develop
will be fairly isolated. Additionally, there is the possibility
that some snow may fall across the San Francisco peaks but with
snow levels generally above 10,000 ft, any accumulation will be
light. A couple more facets of this low will be the cooler
temperatures across the region along with some gusty winds.
Saturday will be the coolest of the the next couple of days with
temperatures averaging 5-10 degrees below normal across the entire
forecast area.

The low moves off to the northeast by late Saturday and we see
things starting to clear out as a ridge starts to build across the
west. Temperatures will warm and conditions dry out once again
heading into the new week. A couple of kinks in the forecast come in
the shape of cut off lows and shortwave troughs. A trough looks to
drop down from the north, crossing through the Four Corners area on
Tuesday. This may bring a chance for some isolated showers and gusty
winds. A second cut off low may also develop along the California
coast but the strength and depth of the approaching Four Corners
trough early in the week looks like it may keep this low off to our
west before deflecting the low off to the north as the ridge builds
over the southwest during the middle of the week. Lots of moving
parts in this forecast with plenty to grab our attention over the
coming days.

&&

.AVIATION...Friday 20/18Z through Saturday 21/18Z...VFR conditions
will prevail for most areas through 06Z. Expect south to
southwest winds at 10-20 kts gusting to 20-30 kts through 01Z
then diminishing. After 06Z, scattered -SHRA/-TSRA and MVFR
conditions west of a KPRC-KPGA line after 06Z with chances
gradually increasing and spreading eastward through 18Z.

OUTLOOK...Saturday 21/18Z through Monday 23/18Z...Scattered
-SHRA/-TSRA and MVFR conditions will continue during the day
 Saturday. Greatest chances will be along and east of a KPRC-KFLG-
 KPGA line. VFR conditions with clear skies return later Saturday
 night into Sunday. West-northwest winds at 10-20 kts on
 Saturday, then variable winds mostly 10 kts or less for Sunday
 and Monday.

&&

.FIRE WEATHER...Today and Saturday...An area of low pressure
approaching from the west will bring increasing chances for showers
and thunderstorms today through Saturday. South winds 15-25 mph this
afternoon, followed by west-northwest winds 10-20 mph Saturday.

Sunday through Tuesday...Warmer and drier Sunday and Monday with
afternoon humidity in the 10-20% range. Humidity increases slightly
Tuesday with a 10-15% chance of rain. Light west to north winds
under 15 mph are likely Sunday and Monday, with northerly winds 10-
20 mph Tuesday.

&&

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

&&

$$

PUBLIC...MCT/Meola
AVIATION...McCollum
FIRE WEATHER...MAS

For Northern Arizona weather information visit
weather.gov/flagstaff