Winter Storm Warning 4, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
1025 AM MST Sat Mar 30 2024

.SYNOPSIS...A potent Pacific storm will deliver high country
snowfall and valley rainfall Saturday evening through Monday.
Gusty southwest winds will subside with the onset of the
precipitation. Warmer and drier conditions are forecast by the
middle of next week.

&&

.UPDATE...Breezy south winds are developing this morning with
gusts reaching into the 35 to 45 mph range already. Expect these
gusts to become more widespread this morning and increase a bit
more this afternoon in advance of our approaching storm system.
The deep low can be seen spinning off the coast of central
California this morning, spreading moderate to heavy rain across
southern California. Conditions should remain dry for Arizona
until later this evening with precipitation chances developing
over far western Coconino County by 5 PM. This is a strong frontal
band and is forecast to drop significant precipitation
accumulations across northern Arizona tonight. Morning guidance so
far is hinting that even higher snowfall accumulations are
possible in the Flagstaff area so stay tuned for updates this
afternoon.

&&

.PREV DISCUSSION /513 AM MST/...All eyes on the deep upper low west
of San Francisco this morning, with a robust cold front
stretching through western Nevada to near Los Angeles. This low
will dive toward San Diego today, filling a bit and fracturing
into two lobes as it does. This will not stop the progression of
the cold front, but it will weaken as it moves eastward, likely
peaking over western and central Arizona tonight. A cold and
highly unstable airmass trails the front for late Sunday into
Monday, with some strong convection possible over our southern
zones. Let's get into some details...

Ahead of the cold front, vigorous southwest gradients continue today
and through most of the tonight. Many sites have at least partially
decoupled overnight, but we will start to mix early this morning
with a very wind day expected. Winds continue into the evening but
we will expire the current Wind Advisory right as areas of rain and
snow move into the picture, with the Winter Weather Advisory then
taking precedence.

The cold front then moves into the western CWA around sunset and
moves toward the I-17 corridor a bit after Midnight MST and marches
eastward through Sunday morning. The front loses some of its punch
as it moves eastward, especially as it reaches the White Mountains.
However, our western/central zones, especially the notorious I-17
corridor, will see a few prolific hours of rain and snowfall in the
overnight hours tonight. There is a pronounced dry slot behind the
front and precipitation should end quickly, with several hours
elapsing before convective showers develop.

There are some temperature profile issues tonight. The initial
airmass is fairly warm and this will limit some snow accumulation.
Steep lapse rates within the cold front also indicate that areas of
heavier, frozen precipitation may be ice pellets and graupel, not
fluffy dendrites. We took accumulations down a bit due to these
factors and transitioned the Winter Storm Watch into a Winter
Weather Advisory.

Important note, the Winter Weather Advisory mostly deals with the
frontal precipitation event, not the following convective showers
for Sunday night and Monday. This will have to be watched as the
location and strength of these showers may necessitate extending
some of the segments as we head into Sunday afternoon.

Lingering convection Tuesday will be isolated and the temperatures
will warm, with at least a few days of ridging then following that.
Possible troughiness looms again for next weekend, but let's deal
with this one for now.

&&

.AVIATION...Saturday 30/18Z through Sunday 31/18Z...VFR conditions
will remain through 03Z, before decreasing ceilings/visibilities
become likely with SHRA/SHSN increasing west to east.
MVFR/IFR/LIFR conditions anticipated between 03Z-15Z. Prior to
showers overnight/tomorrow morning, expect widespread winds
gusting 35-45kts. By 12Z, gusty winds will become limited to
eastern AZ and near stronger storm cells.

OUTLOOK...Sunday 31/18Z through Tuesday 02/18Z...SHRA/SHSN will
continue through much of the outlook period, keeping MVFR/IFR
condition around through at least 00Z Tuesday. A gradual
improvement of conditions is expected throughout Tuesday, with
isolated showers remaining near the White Mountains. Look for SW
winds 10-20 kts Sunday, W-NW winds of 5-15 kts Monday, and
northerly winds on Tuesday.

&&

.FIRE WEATHER...Today and Sunday...Strong south-southwest winds
will gust at 35 to 50 mph today. Minimum RH values will be in the
teens for portions of the Little Colorado River Valley and Navajo
Nation. Expect widespread rain and snow beginning this evening from
west to east, continuing through Sunday. Winds weaken Sunday while
humidity values increase substantially.

Monday through Wednesday...Rain and snow showers continue Monday
with a chance of afternoon thunderstorms. Westerly winds at 10 to 20
mph Monday shift to northerly by Tuesday. Showers linger on Tuesday
near the White Mountains with warmer and drier conditions elsewhere.
Conditions will continue to improve Wednesday.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 8 PM MST /9 PM MDT/ this evening for AZZ004-
006-007-009-011>017-039-040.

Winter Weather Advisory from 8 PM MST /9 PM MDT/ this evening to
8 AM MST /9 AM MDT/ Sunday for AZZ004-006-007-015.

Wind Advisory until 8 PM MST /9 PM MDT/ this evening for AZZ005-
008-010-018-037-038.

Winter Weather Advisory from midnight tonight to 5 PM MST Sunday
for AZZ016.

Winter Weather Advisory from noon Sunday to noon MST Monday for
AZZ017.

&&

PUBLIC...MCT/Peterson
AVIATION...Konieczny
FIRE WEATHER...JM

For Northern Arizona weather information visit
weather.gov/flagstaff