Flash Flood and Heavy Snow in Arizona, March 18 to 20, 2020

Name: Flash Flood and Heavy Snow in Arizona, March 18 to 20, 2020
Start: 2020-03-18T03:00
End: 2020-03-20T19:00
Location: Arizona

March 18 to 20, 2020 · NWS FGZ · 7 events in 7 counties and zones

A winter storm brought heavy rain and snow to northern Arizona.

Where it happened

Every event with a place to put it; 6 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 7

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What happened

The episode as NWS FGZ wrote it up.

A winter storm brought heavy rain and snow to northern Arizona.

What forecasters said that day

The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Flagstaff, AZ wrote its last area forecast discussion before the first event at Mar 17, 8:50 PM MST, 6 hours 10 minutes earlier.

Area forecast discussion, Mar 17, 8:50 PM MST, 6 hours 10 minutes before

Area Forecast Discussion
National Weather Service Flagstaff AZ
850 PM MST Tue Mar 17 2020

.SYNOPSIS...A strong Pacific storm will move into the area early
Wednesday, spreading areas of valley rain and accumulating
mountain snow across the region through Thursday. A variety of
winter weather warnings and advisories have been issued, stay
safe.

&&

.UPDATE...Relatively warm and locally breezy conditions continue
this evening under a southerly flow aloft. Clouds are beginning to
increase across western Arizona and will gradually increase and
spread east overnight. Trimmed back precipitation chances this
evening as the only radar echoes showing up are in Mohave county
and areas west. Expect scattered showers to develop across
western Arizona after midnight, increasing in coverage by daybreak
Wednesday. Please see the previous discussion below for details
on the upcoming winter storm system.

&&

.PREV DISCUSSION /300 PM MST/...We are on track for a significant
Winter Storm for Wednesday and Thursday. 12Z models showing the
southern portion of the trough ejecting into southwest Arizona
Wednesday afternoon and through the Four Corners by Thursday
morning. The southern part of the low is more in phase now,
compared to model runs from Monday. There is also a significant
post-frontal unstable upslope event that sets up along the
Mogollon Rim, behind the cold front.

So, we expect frontal precipitation along and west of the I-17
corridor tonight and Wednesday morning. Then, the southern part of
the low ejects through the state and this is when the bulk of the
precipitation arrives in central and east-central Arizona. Looking
at roughly mid-afternoon Wednesday, through late evening. After
Midnight MST Wednesday night, the post-frontal precipitation
develops, slowly tapering off through Thursday morning.

The bulk of the heavier snow will be above 6000 feet and focused
on the central Mogollon Rim. Rainfall will definitely be enough
to kick off another hydrological event south of the Mogollon Rim.

The Winter Storm Watch has been upgraded to a Winter Storm Warning
and Snow Advisories have been added south of the rim.

Only slight chances of precipitation will remain Friday and expect
drier conditions into the weekend out ahead of another potential
weather system.

Friday, the upper low over California and Nevada will begin to
degrade. Moisture wrapping around the decaying low will produce
slight chances of showers in western Yavapai and Coconino Counties
Friday morning and afternoon. The mean southwesterly flow will
transport moisture out of western zones by Friday evening.

Saturday and beyond, drier conditions look solid for the weekend
under light southwesterly flow aloft. Model solutions are
diverging on any potential weather for Monday that could stem
from another Eastern Pacific weather system. Chances of
precipitation remain in the forecast from late Sunday night
through Monday night, but will need to be assessed over the
coming forecast packages.

&&

.AVIATION...For the 06Z package...Mountain peaks and ridges are
obscured west of the I-17/Hwy-89 corridor with MVFR and some IFR
conditions across much of this area. Showers are moving into the
area from the west with snow levels above 6500 ft. Rain and snow
showers will spread east to a KPGA-KFLG-KPAN line by 12Z Wednesday
and continue eastward to the New Mexico border through the day with
snow levels falling to 6000 ft MSL. Expect mostly MVFR to IFR
conditions associated with these showers through the TAF period.
Winds will be south to southwest at 10-15 kts gusting 20-30 kts
between 17Z and 02Z Thursday. Aviation discussion not updated for
TAF amendments.

&&

.FIRE WEATHER...Localized gusty south to southwest winds will
continue tonight. A significant winter storm arrives early Wednesday
and will bring widespread valley rain and mountain snow through
Thursday morning. More isolated showers through Thursday night.

Friday through Sunday...Slight chances of precipitation Friday. Dry
weather and warmer conditions return on Saturday and Sunday.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...Winter Weather Advisory from
6 PM Wednesday to 6 AM MST Thursday FOR AZZ008-018.

Winter Storm Warning from 6 AM Wednesday to 6 AM MST Thursday
FOR AZZ004-015.

Winter Storm Warning from 6 PM Wednesday to 6 AM MST Thursday
FOR AZZ017.

Winter Storm Warning from noon Wednesday to 6 AM MST Thursday
FOR AZZ016.

&&

PUBLIC...MCT/Peterson/NL
AVIATION...DB
FIRE WEATHER...NL

For Northern Arizona weather information visit
weather.gov/flagstaff

The radar

The Flagstaff radar (KFSX), 150 km away, was scanning. The volume nearest the first event began at 08:50 UTC.

Open the radar archive at this moment

Event by event

6 heavy snow, 1 flash flood. Local standard time, as filed.

Heavy Snow, Western Mogollon Rim

When: March 18, 3:00 AM MST to March 20, 7:00 PM MST
Where: Western Mogollon Rim forecast zone
Reported by: Trained Spotter
Coordinates: 35.839, -111.770 (the zone’s center; the record gives no point)

Heavy snow fell across the Western Mogollon Rim. Here are some of the snowfall totals in inches: Mountainaire and Munds Park 9.5, Flagstaff Airport 14.5, Bellemont 8.1, and Kachina Village 17. ADOT reported at least 14 collision on Interstate -40 west of Flagstaff that caused major delays and road closures (one section of the interstate was closed for over 13 hours).

Heavy Snow, Kaibab Plateau

When: March 18, 3:25 AM MST to March 19, 7:00 PM MST
Where: Kaibab Plateau forecast zone
Reported by: COOP Observer
Coordinates: 35.839, -111.770 (the zone’s center; the record gives no point)

The North Rim of the Grand Canyon received 11.5 inches of snow by the evening of March 19.

Heavy Snow, Grand Canyon Country

When: March 18, 3:25 AM MST to March 19, 7:00 PM MST
Where: Grand Canyon Country forecast zone
Reported by: COOP Observer
Coordinates: 35.839, -111.770 (the zone’s center; the record gives no point)

The North Rim of the Grand Canyon received 11.5 inches of snow by the evening of March 19.

Heavy Snow, Yavapai County Mountains

When: March 18, 4:00 PM MST to March 19, 10:00 AM MST
Where: Yavapai County Mountains forecast zone
Reported by: Trained Spotter
Coordinates: 34.600, -112.554 (the zone’s center; the record gives no point)

A spotter in Crown King reported 8 inches of snow at around 6000 feet elevation at 800 AM. Seven inches of snow fell at the Courthouse in Prescott at 5,400 feet. Eight inches of snow fell in Walker at 6,400 feet.

Heavy Snow, Eastern Mogollon Rim

When: March 18, 6:00 PM MST to March 19, 6:00 PM MST
Where: Eastern Mogollon Rim forecast zone
Reported by: Trained Spotter
Coordinates: 35.620, -111.045 (the zone’s center; the record gives no point)

A trained spotter in Forest Lakes reported 12 inches of new snow.

Heavy Snow, White Mountains

When: March 18, 6:00 PM MST to March 19, 6:00 PM MST
Where: White Mountains forecast zone
Reported by: Public
Coordinates: 35.398, -109.905 (the zone’s center; the record gives no point)

Eight inches of snow fell in Nutrioso by 900 AM on March 19. Nine inches of snow fell in Alpine. Pinetop-Lakeside received 8.5 inches of snow by 700 AM on March 19.

Flash Flood, Gila

When: March 19, 1:50 AM MST to March 20, 1:50 AM MST
Where: Gila County, 2.46 mi WNW of (0e4)payson Arpt to 2.32 mi NW of (0e4)payson Arpt
Cause: Heavy Rain
Reported by: Public
Coordinates: 34.264, -111.390

The East Verde River rose 4 feet in East Verde Estates.

What these are

Heavy Snow: Snowfall reaching the local warning threshold without the other hazards of a winter storm.
Flash Flood: Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Arizona in 2020 Every state in 2020 This day in weather history Warnings in Arizona, March 2020

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 877308, 877309, 877310, 877311, 877312, 877313, 877307.