Deep monsoon moisture over easern Arizona allowed at least one thunderstorm with heavy rain to form over the Little Colorado River basin above St Johns.
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The episode as NWS FGZ wrote it up.
Deep monsoon moisture over easern Arizona allowed at least one thunderstorm with heavy rain to form over the Little Colorado River basin above St Johns.
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 Aug 1, 2:43 PM MST, 17 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 243 PM MST Thu Aug 1 2024 .SYNOPSIS...Shower and thunderstorm activity will increase into the weekend and then remain steady through next week. Above average temperatures will also continue. && .DISCUSSION...An area of low pressure over the northern part of Baja California is circulating moisture over Arizona today. Showers and thunderstorms have formed east of Flagstaff today and are generally moving in a western direction. The high pressure that has been centered over Texas is starting to move northwest and will continue to do so through Saturday... reaching a position near the Four Corners. This will be in a much more favorable position to bring monsoon moisture over northern Arizona...with moderate grade activity expected into next week. The primary hazards will be gusty/erratic outflow winds, small hail, lightning, and brief heavy rainfall. Local flash flooding is possible in some of the heavier storms. Even with the increased activity, temperatures will continue to be above average...up to 10 degrees in some locations. As we progress through the summer season, tropical storms tend to develop off the western coast of Mexico. Tropical Storm Carlotta is currently around 400 miles south-southwest of Cabo San Lucas and is expected to move westward. Longer rage models depict one or two more storms developing and moving west to northwest. Depending on the track and strength of storms of in this area, a surge of moisture across the Sea of Cortez can impact Arizona. Something to keep an eye on late next week. && .AVIATION...Thursday 01/18Z through Friday 02/18Z...Mainly VFR conditions are expected through the period with SCT-BKN cloud cover. Isolated to scattered -SHRA/-TSRA are forecast from 20Z-03Z, along and south of a KCMR-KFLG-KINW-KRQE line, tapering thereafter. Brief periods of MVFR conditions are likely in stronger storms. Outside of erratic outflow winds of up to 35 kts, anticipate east to southerly winds 5-10 kts. OUTLOOK...Friday 02/18Z through Sunday 04/18Z...Plan on daily chances for scattered to numerous -SHRA/-TSRA each afternoon and evening through the period. Expect afternoon southwest to west winds 5-15 kts, outside of any outflow gusts from storms. && .FIRE WEATHER...Tonight through Saturday...Isolated showers and thunderstorms persist for the remainder of the evening mainly south and west of the Mogollon Rim. Good humidity recovery is expected overnight with light and variable winds. Scattered showers and storms are forecast each afternoon/evening Friday and Saturday across much of northern Arizona. Outside of erratic outflow winds of up to 40 mph from storms, anticipate southwest winds 5 to 15 mph each afternoon. Sunday through Tuesday...The active monsoonal pattern continues into next week with daily chances for showers and thunderstorms. Widespread wetting rains (>0.10") are likely during this time. Temperatures remain 5 degrees above average with westerly winds, 5 to 10 mph, each afternoon. && .FGZ WATCHES/WARNINGS/ADVISORIES...None. && PUBLIC...MAS AVIATION...LaGuardia FIRE WEATHER...LaGuardia For Northern Arizona weather information visit weather.gov/flagstaff
The Flagstaff radar (KFSX), 172 km away, was scanning. The volume nearest the first event began at 21:58 UTC.
1 flash flood. Local standard time, as filed.
Heavy rain caused an incrase in the water flowing down the Little Colorado River near St Johns. The flow started to incrase at 1500 and peaked at around 2 feet higher at 1700. The river dropped back to near normal at 2100.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2024Every state in 2024This day in weather historyWarnings in Arizona, August 2024
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: 1212748.