A moderate to strong atmospheric river aligned over South-central Arizona and led to widespread light to moderate rain across the region. Rain began falling the night of the 23rd and lasted through the evening of the 24th.
Every event with a place to put it. 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 PSR wrote it up.
A moderate to strong atmospheric river aligned over South-central Arizona and led to widespread light to moderate rain across the region. Rain began falling the night of the 23rd and lasted through the evening of the 24th. The Phoenix area measured 1-2 inches and most foothill and mountainous areas measured 2-3 inches, with a few localized spots measuring 3-4 inches. The high rainfall amounts led to minor urban flooding and elevated flows in typically dry washes as well as in several major creeks and rivers. Elevated flows made at least one low water crossing in the Cave Creek area impassable. Flows coming down from Pinal Peak, within the 2021 Telegraph Fire burn area, also made some rural roads in the El Capitan area impassable. Tonto Creek in Tonto Basin experienced a 2-week long period with flow at or above action stage, beginning in the evening of the 24th.
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 Phoenix, AZ wrote its last area forecast discussion before the first event at Dec 24, 12:17 PM MST, 43 minutes earlier.
Area Forecast Discussion National Weather Service Phoenix AZ 1217 PM MST Fri Dec 24 2021 .UPDATE... Updated Aviation discussion. && .SYNOPSIS... Showers will continue through this morning with additional rain chances this weekend. Today's rain will be beneficial for most areas. But, wet roads will make road travel more hazardous and flooding potential exists over any burn recent scars as well as in some normally dry washes...especially Tonto Creek. An unsettled weather pattern is likely to continue into next week with additional chances of precipitation while temperatures remain at or below seasonal normals. && .DISCUSSION... Showers are spreading throughout the forecast area marking the shift towards a cooler and wetter regime. So far, most rainfall totals have been under 0.10" with a few pockets of higher amounts. Shower activity will continue to increase from west to east this morning as latest guidance and observational trends show the bulk of activity falling now through the early afternoon. Activity will wane from west to east this afternoon while chances beyond trend downwards each successive day this weekend. Rainfall rates of 0.10-0.25 in/hr have been observed so far and should persist throughout the event. Temporary localized higher rates cannot completely be ruled out, especially for areas subject to upslope flow. Rainfall totals will generally rise from west to east across the CWA with 0.10-0.50” most likely for southeastern CA and southwestern AZ, and 0.50-1.50” for south-central Arizona. The latest forecast mirrors ensemble means with widespread totals of 0.75-1.25” across the Phoenix metro while higher totals, close to 2 inches, focus over the higher terrain north and east of Phoenix. The main driver for the weather shift is an upper level low that shows well on water vapor imagery just of the SoCal coast. The on- going steady stream of moisture advection will intensify later this morning as the main circulation ejects into the Southwest today. Integrated Water Vapor transport guidance still shows 50-80% chance for 500-750 kg/m/s of water vapor streaming into the region which means this atmospheric river will be seasonally significant and near climatological maximums in the NAEFS record. When all is said and done, this amount of moisture means most places will see at least some rain and some places may see their wettest December day(s) in decades. The rain will be beneficial for most areas but there is a limited flood concern within the WPC’s latest marginal Excessive Rainfall Outlook. The lower rainfall rates should give plenty of time for soils to absorb the rain but burn scar areas and some normally dry washes could see some flow. Tonto Creek is forecast to exceed action stage by early this afternoon, potentially inundating low water crossings. The forecast beyond remains ambiguous but ensemble guidance is hinting at another shortwave moving out of the Gulf of Alaska and southward along the West Coast Tuesday. More shortwaves are also possible later in the week but guidance uncertainty remains fairly high. Regardless of uncertainties, successive waves will reinforce the upper level trough that will lead to cooler temperatures at or even slightly below seasonal normals through the week. Fog will also loom for some early mornings following very wet periods, especially within any river valleys or low spots where cooler air may pool. && .AVIATION...Updated at 1915Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: A strong short wave within southwesterly flow aloft is tapping into rich moisture from lower latitudes to produce widespread MVFR ceilings and IFR visibilities in showers this morning. The wave is in the process of weakening as it moves across Arizona. Hi-res models are in good agreement that the shower activity will decrease in coverage significantly after about 21Z. But, before then, the low ceilings and visibilities will continue (locally IFR ceilings) with a considerable amount of fluctuation from one TAF site to another at any given hour depending upon the localized shower intensities and proximity of hills/mountains to the airfield. Even after 21Z, scattered showers and lingering low level moisture will continue to cause problematic ceilings though not as bad as the previous hours. If any form, they could easily bring brief LIFR conditions. There is about a 10% chance of thunderstorms this afternoon (too low to reflect in the TAFs). Expect much better conditions this evening but with lingering sct cumulus and bkn altocumulus/altostratus. Overnight, lower ceilings may develop AOA FL050 and some spotty very light showers may develop during the day Saturday - but nothing like today. Southeast California/Southwest Arizona including KIPL and KBLH: The main band of showers and lower ceilings is east of the TAF sites. But lingering low level moisture and some very modest instability will keep SCT040-060 and BKN080-100 going through the afternoon could even have some localized BKN040-060. The potential for thunderstorms at the TAF sites is less than 10% (higher to the east and southeast). Strong southwesterly winds with gusts of 25-30kts (possibly as high as 35 kts) can be expected through the afternoon before weakening this evening. Couldn't rule out brief reductions in visibility at KIPL but that is more likely in desert areas west of the airfield. && .FIRE WEATHER... Sunday through Thursday: Temperatures will remain cool at or slightly below normal. Low level moisture will remain present keeping Min RH values at or above 40% while overnight recovery surge above 60-70%. Winds may be concerning at times with occasional gusts of 20-30 mph some days, but which days will be the breeziest remains ambiguous. Showers will decrease Sunday-Monday but another wave of showers seems more likely Tuesday. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && DISCUSSION...12 AVIATION...AJ FIRE WEATHER...12
The national radar mosaic for the moment the first event began.
2 flood. Local standard time, as filed.
A social media photo posted at 1702MST showed a low water crossing along Maddock Road, near 26th Street, was impassable due to flood waters. Timing of impacts estimated from radar. A measured 1.5 to 2.5 inches of rain had fallen in the area by 1700MST. No damages or injuries were reported.
A trained spotter shared videos around 1500MST of elevated flow through typically dry washes coming down from the Pinal mountains, within the 2021 Telegraph fire burn area. Flood waters made parts of Horseshoe Creek Road, a dirt road, impassable. The spotter said it had been raining for 6 to 7 hours before the flooding began. An NWS Employee that happened to be driving through the area also shared an image of significant flow through a wash along the side of Highway-77. Measured rainfall amounts were up to 2 to 2.5 inches over the Pinal mountain by early in the afternoon of the 24th. Timing of impacts estimated. No damages or injuries were reported.
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, December 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: 992786, 993082.