A shortwave trough moving across Arizona brought scattered shower and thunderstorm activity to northern Arizona. One of the showers produce a gust front that spun up a vortex.
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The episode as NWS FGZ wrote it up.
A shortwave trough moving across Arizona brought scattered shower and thunderstorm activity to northern Arizona. One of the showers produce a gust front that spun up a vortex.
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 Apr 21, 9:21 AM MST, 2 hours 56 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 921 AM MST Tue Apr 21 2020 .SYNOPSIS...A weather system will bring showers to the region through early evening, most widespread along and north of Interstate 40. A few thunderstorms will also be possible. From Wednesday through the remainder of the week, expect warming temperatures and dry weather. && .DISCUSSION...Scattered shower activity is ongoing this morning from Fraziers Well to the Grand Canyon and northward. We are beginning to see some cumulus development to the south as daytime heating begins. This is all in response to yet another shortwave trough set to cross the state today. As the surface continues to warm, expect widespread shower activity to develop generally from Prescott to Payson and northward. Coverage of showers will be greatest along and north of Interstate 40. Model soundings indicate anywhere from 200-400 J/kg of CAPE this afternoon, with LI values from -1 to -3 C. Therefore, expect a few thunderstorms to develop as well with small hail and lightning being the primary hazards. Otherwise, expect mild temperatures with typical west to southwest afternoon breezes. The trough will push east of the state tonight, with decreasing shower chances and clearing skies. A weak system will brush the Four Corners region on Thursday, with breezy northwest winds developing. Otherwise, high pressure will be the dominate weather feature for the next several days. By the weekend, most mountain locations will see temperatures in the upper 60s to mid 70s with many mid elevation locations such as Winslow and Prescott climbing into the 80 degree range. The low desert of central Arizona and the Phantom Ranch area will see high temperatures in the mid to upper 90s. Even warmer weather is possible as we head into next week as strong high pressure becomes centered over Arizona. At this time, record daily high temperatures look to be within reach in the Tuesday-Wednesday timeframe. Stay tuned. && .PREV DISCUSSION /306 AM MST/...Yet another shortwave trough will move across northern Arizona today. A cool air mass aloft associated with the trough will combine with daytime heating to destabilize the air mass. As a result, starting late this morning and lasting through the early evening a widespread area of showers with embedded thunderstorms will develop primarily along and north of Interstate-40. Temperatures should remain on the mild side. Look for the usual afternoon southwest breezes shifting to a more westerly direction later in the afternoon. All shower activity is expected to end by mid evening as the current trough moves to the east. From Wednesday onward...High pressure will take control of the southwest United States. A fast moving and weak weather disturbance will bring a slight chance of showers to the Four Corners on Thursday and kick up some northwesterly breezes. Other than that warm temperatures, mainly clear skies and light winds are in store by the end of the week as high pressure builds over Arizona. By the weekend most mountain locations will see temperatures in the upper 60s to mid 70s with many mid elevation locations such as Winslow and Prescott climbing into the 80 degree range. The low desert of central Arizona and the Phantom Ranch area will see high temperatures in the mid to upper 90s. The inevitable dry and hot progression of spring in Arizona has begun. && .AVIATION...For the 18Z package...Widespread showers and a few thunderstorms will develop through the early evening hours along and north of a KPRC-KPAN-KINW line. Surface winds will generally be westerly at 5-15 kts with gusts of 15-25 kts. Winds will weaken after sunset. Precipitation chances will decrease from west to east this evening. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Chances for showers and thunderstorms increase through this morning and are highest in the afternoon. Dry and warmer conditions will return Wednesday. Westerly breezes today will become north-northwesterly by Wednesday. Thursday through Saturday...Dry weather with warmer than normal temperatures are expected through the period. Winds will be gustiest on Thursday before becoming lighter for Friday and Saturday. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && PUBLIC...TPS/McCollum AVIATION...TPS FIRE WEATHER...NL For Northern Arizona weather information visit weather.gov/flagstaff
Special Weather Statement National Weather Service Flagstaff AZ 1051 AM MDT Tue Apr 21 2020 AZZ009-211745- Northeast Plateaus and Mesas Hwy 264 Northward- 1051 AM MDT Tue Apr 21 2020 ...SIGNIFICANT WEATHER ADVISORY FOR COCONINO COUNTY UNTIL 1145 AM MDT... At 1048 AM MDT, Doppler radar was tracking a thunderstorm near Antelope Creek Basin, or 19 miles south of Page. This storm was nearly stationary. Pea size hail will be possible with this storm. Locations impacted include... Antelope Creek Basin and Antelope Canyon. PRECAUTIONARY/PREPAREDNESS ACTIONS... Heavy rainfall is also occurring with this storm, and may lead to flowing water in washes and slot canyons. Do not enter or drive your vehicle through flooded areas or roadways. && LAT...LON 3647 11146 3671 11153 3677 11127 3660 11118 TIME...MOT...LOC 1648Z 131DEG 0KT 3664 11136 MAS
Special Weather Statement National Weather Service Flagstaff AZ 1118 AM MDT Tue Apr 21 2020 AZZ012-211815- Little Colorado River Valley in Coconino County- 1118 AM MDT Tue Apr 21 2020 ...SIGNIFICANT WEATHER ADVISORY FOR COCONINO COUNTY UNTIL 1215 PM MDT/1115 AM MST/... At 1116 AM MDT/1016 AM MST/, Doppler radar was tracking a strong thunderstorm near Gray Mountain, or 31 miles south of Tuba City, moving east at 20 mph. Pea size hail and winds in excess of 30 mph will be possible with this storm. This storm will remain over mainly rural areas of Coconino County. LAT...LON 3559 11147 3577 11147 3580 11117 3559 11116 TIME...MOT...LOC 1716Z 270DEG 18KT 3569 11138 MAS
Special Weather Statement National Weather Service Flagstaff AZ 1045 AM MST Tue Apr 21 2020 AZZ007-008-037-211830- Yavapai County Valleys and Basins-Coconino Plateau-Yavapai County Mountains- 1045 AM MST Tue Apr 21 2020 ...SIGNIFICANT WEATHER ADVISORY FOR YAVAPAI AND COCONINO COUNTIES UNTIL 1130 AM MST... At 1043 AM MST, Doppler radar was tracking a thunderstorm near Seligman, or 46 miles northwest of Chino Valley, moving east at 10 mph. This will impact Interstae 40. Pea size hail and winds in excess of 30 mph will be possible with this storm. Locations impacted include... Seligman. PRECAUTIONARY/PREPAREDNESS ACTIONS... Heavy rainfall is also occurring with this storm, and may lead to localized flooding or ponding of water on roadways. Do not drive your vehicle through flooded roadways. && LAT...LON 3522 11299 3534 11301 3543 11274 3517 11271 TIME...MOT...LOC 1743Z 264DEG 8KT 3529 11296 MAS
Special Weather Statement National Weather Service Flagstaff AZ 1255 PM MDT Tue Apr 21 2020 AZZ007-012-040-211930- Little Colorado River Valley in Coconino County-Coconino Plateau- Northeast Plateaus and Mesas South of Hwy 264- 1255 PM MDT Tue Apr 21 2020 ...SIGNIFICANT WEATHER ADVISORY FOR COCONINO COUNTY UNTIL 130 PM MDT/1230 PM MST/... At 1254 PM MDT/1154 AM MST/, Doppler radar was tracking a strong thunderstorm near Cameron, or 22 miles southeast of Desert View at Grand Canyon, moving east at 20 mph. Pea size hail and winds in excess of 30 mph will be possible with this storm. Locations impacted include... Cameron. PRECAUTIONARY/PREPAREDNESS ACTIONS... Heavy rainfall is also occurring with this storm, and may lead to localized flooding. Do not drive your vehicle through flooded roadways. && LAT...LON 3572 11158 3591 11162 3602 11122 3575 11116 TIME...MOT...LOC 1854Z 259DEG 15KT 3584 11152 MAS
The national radar mosaic for the moment the first event began.
1 dust devil. Local standard time, as filed.
A video on social media showed a whirl of dust at or near the ground near the gust from from a storm. There was no condensation funnel. The wind in the circulation was estimated to be 50 MPH.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2020Every state in 2020This day in weather historyWarnings in Arizona, April 2020
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: 883431.