Red Flag Warning 4, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
1053 AM MST Wed Apr 16 2025

.SYNOPSIS...A weather system will bring dramatic changes to the
weather across northern Arizona starting Thursday with increasing
southwest winds and much cooler temperatures. Chances of rain
showers and snow showers increase Thursday night in the northwest
and will spread across northern Arizona on Friday. Showers will
linger in Apache County into Saturday night. Warmer and drier
weather will make a quick comeback next week.

&&

.UPDATE...A large area of low pressure off the coast of California
is increasing the southwest flow over northern Arizona this
morning. This has transported mid and low lever moisture over the
area. The sounding this morning showed a moist layer up to about
615 mb...then very dry above that. Will make adjustments to the
sky grids for today to increase the cloud cover. May need wind
headlines for some of the area on Thursday.

&&

.PREV DISCUSSION /448 AM MST/...An area of high pressure remains
above the Southwest today, bringing daytime highs to land in the
above normal range this afternoon. This pleasant spring weather is
quickly heading out as cooler/wetter conditions return for the
second half of the week. But before we go further into the details
of the incoming unsettled weather, let's discuss the near-
critical fire weather concerns for today and the critical fire
weather concerns for tomorrow. With an area of low pressure
currently sitting off the California Coast, pressure gradients are
beginning to tighten over Arizona. This synoptic set-up will
bring elevated southwest winds across our CWA later today. And
since we are still ~36 hours out from moisture arriving, relative
humidities are widely below 15%. Winds will be elevated today, but
peak on Thursday. As a result, a Fire Weather Watch is in effect
for Thursday afternoon for much of eastern Arizona. Even though
there is no fire-related product for today, still do you part to
help prevent any fire-starts.

And just as our Fire Weather Watch is set to expire Thursday
evening, rain and high elevation snow showers look to begin across
far northern Arizona. We aren't just dealing with the closed low
in the Pacific that will push more inland, but a stronger trough
will also begin to fall from the Pacific Northwest. These two
disturbances look to combine over the Great Basin Region on
Thursday, bringing in sufficient moisture to northern Arizona.
Showers look to begin as early as 5 PM Thursday across the Kaibab
Plateau and gradually push south and east through Saturday. With
the warm air we've been enjoying the last week or so, it will take
a minute for our snow levels to drop. As precipitation starts,
snow levels will be around 7000-7500'. But as the core of this now
combined trough moves closer to the AZ/UT border, colder air will
funnel in and quickly drop snow levels to 6000-6500'. Our current
forecast shows the Kaibab Plateau and San Fransisco Peaks receiving
5-10" of new snowfall and areas across the Mogollon Rim and White
Mountains landing in the 1-3" range. These totals are for Thursday
night through Saturday evening. The big thing to keep in mind with
these snow amounts is knowing accumulation will be difficult with
the recent warm surface temperatures. Heavier bands of precipitation
could allow for quick accumulation, but this event is certainly more
favorable to be one where snow melts almost as quickly as it falls.
It won't just be the High Country enjoying moisture though, lower
elevation areas look to receive rainfall ranging from 0.20-0.40".

If you do happen to see snow accumulation out of this storm
system, it will likely be gone before the weekend is over. Daytime
highs are forecast to jump right back up to the 60s for higher
elevation locations and 70s and 80s for lower elevation locations
by Sunday afternoon. These warm temperatures will only increase
throughout next week with returning dry conditions too.

&&

.AVIATION...Wednesday 16/18Z through Thursday 17/18Z...VFR
conditions are expected under FEW-SCT middle and upper-level
clouds. Winds are S-SW 10-20 kts with gusts up to 30 kts, becoming
S 5-15 kts after 03Z Thursday.

OUTLOOK...Thursday 17/18Z through Saturday 19/18Z... VFR
conditions through 06Z Friday, then periods of MVFR-IFR in
widespread SHRA/SHSN thereafter. Winds are SW 20-30 kts gusting
to 35-45 kts on Thursday, then SW-W 15-25 kts gusting to 30-40 kts
on Friday. SW winds remain elevated at 10-15 kts overnight
Thursday into Friday morning.

&&

.FIRE WEATHER...Today and Thursday...Critical to Near-Critical fire
weather conditions expected, with a Fire Weather Watch in effect for
Thursday across most of Eastern Arizona. Minimum RH values are at or
below 15% today with winds SW 10-20 mph. Minimum RH remains below
15% in the White Mountains and east of the Mogollon Rim, and is 20-
30% western zones on Thursday. Winds are SW 15-25 mph with gusts up
to 35-45 mph on Thursday.

Friday through Sunday...Widespread rain and high elevation snow
showers forecast for Friday, becoming more scattered on Saturday and
drying out on Sunday. Winds SW-W 15-25 mph on Friday, then W-NW 15
mph or less on Saturday and W 10 mph Sunday. Gusty winds possible
near showers.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Thursday morning through Thursday
evening for AZZ110>114-117-139-140.

&&

PUBLIC...MAS/Konieczny
AVIATION...Lewandowski
FIRE WEATHER...Lewandowski/Bernhart

For Northern Arizona weather information visit
weather.gov/flagstaff