A cold trough moved southward through Nevada and closed off over Arizona as it shifted eastward into New Mexico. This produces showery weather over much of northern Arizona with a band of heavier snow just ahead of the low.
Every event with a place to put it; 3 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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.
The episode as NWS FGZ wrote it up.
A cold trough moved southward through Nevada and closed off over Arizona as it shifted eastward into New Mexico. This produces showery weather over much of northern Arizona with a band of heavier snow just ahead of the low. The heavier precipitation fell along a line from Williams to Window Rock.
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 23, 3:42 AM MST, 2 hours 18 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 342 AM MST Tue Mar 23 2021 .SYNOPSIS...A cold winter storm system will bring rain and mountain snow showers to northern Arizona today through Wednesday, along with breezy conditions. Expect some snow accumulations over the higher elevations. Dry but continued breezy weather is in store Thursday followed by additional chances for showers late Thursday through Friday as yet another weather system moves through the region. && .DISCUSSION...A cold trough is diving southward through Nevada early this morning, and will close off as it shifts eastward through Arizona today and into New Mexico by Wednesday morning. A period of showery weather with some accumulating snow down to around 5500 feet is on the way. With the latest model runs, (including operational GFS/EC as well as HREF and HRRR), there is a signal for an area of heavier and more persistent precipitation from around 5 AM this morning through the afternoon just ahead of the upper low. This area is located northwest of a line from Williams to Window Rock, including Valle, the Grand Canyon north and south rims, over to the Black Mesa including Shonto. Forecast snow amounts were increased with this morning's package in these areas, and a Winter Weather Advisory has been issued from 5 AM this morning through 11 PM tonight. Travel along Hwy 64 from Williams up to the Grand Canyon and the higher elevations of Hwy 160 over Black Mesa could become difficult at times. Farther southeast, snow showers are expected to develop later in the morning and afternoon for the Mogollon Rim region including Flagstaff. With the higher spring sun angle, snow accumulation on the main roadways during the afternoon hours may not be as significant in this area, and no advisory was issued. There is some risk of some enhanced northerly upslope snowfall later in the evening through Wednesday morning for the north side of the rim, including Doney Park, and an advisory may need to be issued later if there continues to be indications that this will occur. For far eastern Arizona including the Chuska Mountains and White Mountains, the heavier precipitation looks like it will occur during the evening hours today through Wednesday morning when snow accumulation is more likely to impact road conditions, and a Winter Weather Advisory has been issued from 5 PM today through 5 PM Wednesday. A brief break in the weather will arrive Wednesday night through most of Thursday, but the next low will already be approaching the state by afternoon bringing stronger southwest winds. Gusts to 40 mph are possible for some areas. Rain and snow chances return for late Thursday through Friday as the low moves south over the state. There is still quite a bit of model variability regarding the details of precip amounts and timing, with some runs keeping a closed low nearby well into the weekend. For now, the highest rain/snow chances in our forecast will be late Thursday through Friday, but we'll continue to monitor the latest guidance for the weekend, stay tuned. && .AVIATION...For the 12Z package...A passing low pressure system will bring increasing chances for rain and snow from northwest to southeast. MVFR ceilings and visibilities are likely, with periods of IFR conditions over higher terrain. South to southwest surface winds at 5-15 kts to shift northerly this afternoon into evening. Expect gusts up to 30 kts this afternoon from KINW-KPAN southeast to KJTC-KSJN. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...A passing low pressure system will bring increasing chances for rain and snow from northwest to southeast today. Winds shift from southerly to northerly today. Chances for showers continue Wednesday, primarily from I-17 eastward. Thursday through Saturday...Another low pressure system is likely to create gusty southwest winds on Thursday, followed by a round of light rain and snow from Thursday night into Friday. Dry and warmer conditions are forecast for Saturday. && .FGZ WATCHES/WARNINGS/ADVISORIES...Winter Weather Advisory until 11 PM MST this evening FOR AZZ004-006-007-009-039. Winter Weather Advisory from 5 PM this afternoon to 5 PM MST Wednesday FOR AZZ017. Winter Weather Advisory from 11 AM this morning to 5 PM MST Wednesday FOR AZZ011. && PUBLIC...JJ AVIATION...NL FIRE WEATHER...NL For Northern Arizona weather information visit weather.gov/flagstaff
The national radar mosaic for the moment the first event began.
3 heavy snow. Local standard time, as filed.
The Flagstaff area received 3 to 9 inches of snow. Other areas include (in inches): 13 miles NNW Flagstaff (8,200 feet) 9.4, Williams 4-8, and Doney Park 3-8.
Ten inches of snow fell 5 miles north of Angell at an elevation of around 5,600 feet.
Very heavy snow developed over the Little Colorado River Valley in Apache County. The community of Witch Well received 19.5 inches of snow. The Concho area received 8 inches of new snow.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2021Every state in 2021This day in weather historyWarnings in Arizona, March 2021
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: 951218, 951416, 951219.