303
FXUS65 KFGZ 301707
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
1007 AM MST Fri Oct 30 2026

.SYNOPSIS...A series of Pacific storm systems will tap into deep
tropical moisture for Friday, with widespread showers and scattered
thunderstorms moving west to east across the state. A Flash Flood
Watch is in effect on Friday for Yavapai and Gila counties. Shower
chances diminish on Saturday, with a more significant storm system
arriving Saturday night through early Monday. This second storm will
produce prolific rainfall totals across the region and a Flash Flood
Watch will be in effect for all of northern and central Arizona.

&&

.DISCUSSION...Moisture transport is underway, featuring a 20-30kt
low-level jet pointed straight up the Gulf of California and into
the Lower Colorado River Valley. This advection is due to a deepening
trough along most of the west coast, as well as sub-tropical jet and
s/wv now located around 29N/120W. This will all come together in the
next few hours and will amplify throughout the day, before tapering
off to the east later this evening.

PW values are very high for this time of year and the rapid influx
of higher dew points across the deserts will quickly destabilize the
atmosphere. As the s/wv approaches, we expect large-scale ascent and
increased shear, leading to a risk of isolated severe weather. Much
of the severe threat will be south of the Mogollon Rim and into the
central deserts, closer in proximity to steep, low-level lapse rates
and higher boundary layer moisture. Isolated rotating storms may
produce large hail and severe wind gusts today in these areas.

As far as overall rainfall, we expect fairly robust totals through
this evening, mainly over Yavapai, western Coconino and northern
Gila counties. These areas are where some upslope may develop, as
well as persistent and training storms. Farther to the north and
northeast, dynamics, moisture transport and upslope are not nearly
as impressive and totals will drop off quickly heading toward the
Four Corners. Within the initial FFA location today, generalized
accumulations of 0.50 to 2.00" are likely, with isolated higher
amounts. Due to already saturated ground, this will be more than
enough to elevate flooding threats by this afternoon.

As the s/wv move east this evening, forcing, instability and shear
drops off in a hurry. By daybreak Saturday through early Saturday
evening, we do not expect much more than isolated rain showers.

By later Saturday evening, this is when the main event begins. The
main trough along the west coast starts to move southeastward as a
significant plume of sub-tropical moisture and s/wv is entrained
around 28N/122W. This air mass will be near records as far as PW is
concerned for this time of year and the phasing of the two systems
will allow for an extended period of moderate to heavy rainfall.

The threat for severe weather with the second system have mostly
diminished, thanks largely to a fully saturated and somewhat cold
column over the state of Arizona. However, later on Sunday and
Sunday night when the parent trough moves through, there could
be some isolated severe along the cold front.

The period of precipitation for the second event will stretch from
Saturday evening through Monday morning, allowing plenty of time for
totals to add up. The sweet spot, as of now, looks to be just east
of the I-17 corridor, where as much as 4-5 inches of rainfall could
fall with the heavier bands. Even within the areas that are not as
phased and not seeing as much of an upslope component, as much as 2
inches may accumulate. This is all on the heels of the rainfall from
Friday, so more than enough to cause serious hydrological issues. A
second FFA was issued for the entire CWA during this time frame and
there are no issues with that.

Behind the final trough passage Monday morning, we quickly dry out
with strong ridging developing for a few days. This will be the time
to catch your breath, as models are hinting at another cut-off low
forming near the end of next week.

This is a dangerous situation, especially pertaining to flooding.
Both flash flooding and then longer term river flooding will be a
problem. Larger stem waterways may be flooding for days after the
event, especially the Little Colorado River and the Verde River.

Don`t dismiss the severe threat for Friday either, especially south
of the Mogollon Rim. Stay tuned to your favorite weather source and
find a way to receive warnings.

&&

.AVIATION...Friday 30/18Z through Saturday 31/18Z...Widespread
VFR/MVFR conditions forecast through the TAF period, but isolated
IFR conditions possible in heavier storms. -SHRA/-TSRA
anticipated through at least 12Z, with heaviest activity along and
west of a KGCN-KFLG-KSOW through 00Z, shifting east of a KPGA-
KINW-KPAN line afterwards. Gusty/erratic winds likely near/in
storms, with southerly winds 5-15 kts otherwise.

OUTLOOK...Saturday 31/18Z through Monday 02/18Z...A brief lull in
-SHRA/-TSRA is expected through 00Z Sunday, before heavy rain and
 isolated thunderstorms return. Significant rainfall forecast for
 much of Yavapai County and northern Gila County, but heavy
 rainfall is forecast for much of northern AZ. Thunderstorms are
 less likely on Sunday, but still possible. Activity will
 gradually diminish west to east after 12Z Monday. Gusty/erratic
 winds likely near showers/storms, with southerly winds 10-25 kts
 Saturday and Sunday, becoming northwesterly winds on Monday.

&&

.FIRE WEATHER...Friday and Saturday...Rapidly increasing chances
for showers and thunderstorms today, starting in the western zones
this morning and moving to the eastern zones this evening. Some of
the higher rain totals today are likely over Yavapai and northern
Gila counties, where flooding is possible. There is also a threat
for isolated severe thunderstorms through this afternoon, primarily
south of the Mogollon Rim. By Saturday, a brief lull develops with
only isolated rain showers in the forecast through early Saturday
evening. Winds each day, outside of thunderstorms, are generally
light. Expect daytime southerly winds 5 to 15 mph.

Sunday through Tuesday...Widespread moderate to heavy rainfall from
Saturday night through Monday morning. Some of the heaviest totals
are likely along and south of the Mogollon Rim. Flooding is likely.
The threat for thunderstorms has diminished, but a cold front Sunday
night may spawn a few stronger storms as it moves from northwest to
southeast. Expect southwest winds 10 to 20 mph, with gusts a high as
30 mph Sunday. Winds turn west to northwest at 10 to 20 mph Monday
and northeast 5 to 15 mph for Tuesday.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Saturday evening through late Sunday night for
AZZ004>018-037>040.

Flood Watch through this evening for AZZ008-018-037-038.

&&

$$

PUBLIC...Peterson
AVIATION...Konieczny
FIRE WEATHER...Peterson

For Northern Arizona weather information visit
weather.gov/flagstaff