A weak inverted trough moving across southwest Arizona and southeast California along with daytime heating resulted in the development of isolated thunderstorms over Joshua Tree National Park. High moisture levels in place allowed for these thunderstorms to be efficient rainfall producers, leading to locally high rainfall amounts.
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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 weak inverted trough moving across southwest Arizona and southeast California along with daytime heating resulted in the development of isolated thunderstorms over Joshua Tree National Park. High moisture levels in place allowed for these thunderstorms to be efficient rainfall producers, leading to locally high rainfall amounts. Officials with Joshua Tree National Park reported that running washes led to swiftly moving water flowing over several roads in the park. No injuries were reported.
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 Jul 28, 10:54 AM PST, 1 hour 40 minutes earlier.
Area Forecast Discussion National Weather Service Phoenix AZ 1154 AM MST Wed Jul 28 2021 .UPDATE...Updated 18Z Aviation Discussion. && .SYNOPSIS... One more day of warmer and minimal storm chances today before rain chances increase late in the week. Another weather disturbance expected to affect the region bringing a return to more widespread shower and thunderstorm activity starting Thursday afternoon, likely persisting into the weekend. Drier conditions should then prevail by early next week. && .DISCUSSION... Monsoon activity across the region has returned to a more typical pattern with storms mainly developing over the high terrain during the afternoon before sending outflows into the lower deserts. An overall drier atmosphere across much of southern Arizona yesterday limited convection to a degree, but an organized outflow with gusty winds and dust still managed to work its way through much of the south-central Arizona lower deserts. Arizona and southern California remain under weak south to southeasterly flow with the subtropical high now positioned across the Central Plains. Despite yesterday's outflow moistening up the boundary layer further, additional drying aloft today and daytime mixing is expected to bring less favorable conditions for storms this afternoon and evening. The 00Z HREF agrees with the lower potential compared to yesterday, showing isolated to scattered storms this afternoon along the Mogollon Rim, over extreme southeast Arizona and maybe a few showers and weak storms over La Paz and eastern Riverside Counties. The potential for organized storm outflows into the lower deserts is considerably lower today than yesterday. The semi quiet monsoon period will quickly come to an end on Thursday as a well defined, but weakening upper level trough currently moving westward through southern Texas moves into the region. During the day Thursday, broad upper level ascent will spread westward across much of Arizona as the trough enters the region. Moisture levels and instability will be sufficient for scattered to possibly widespread storms developing across the eastern Arizona high terrain Thursday afternoon with strong winds, heavy rainfall, and localized flooding all possible. There will also likely be some isolated storms developing as far west as the Lower CO River Valley Thursday afternoon, but instability will be much more limited farther west. As the inverted trough progresses across Sonora Mexico and southern Arizona Thursday evening into the early overnight hours, additional storm development will be possible into the lower deserts. A lower end scenario which seems to be the current preferred solution (supported by the latest 06Z HRRR) would mean isolated storms across the lower deserts along a westward advancing outflow. A higher end, but less likely scenario would result in a larger cluster of storms and associated cold pool advancing off the mountains into the lower deserts, potentially including the Phoenix area. Strong gusty winds and blowing dust will be the most likely threats over the lower deserts Thursday evening with locally heavy rainfall also a possibility. Isolated to scattered showers and storms will remain possible Thursday night, reaching as far west as southeast California. The inverted trough is forecast to exit the region to the northwest Friday morning, but not before spreading modest moisture throughout our area. Storm chances for Friday now look to be a bit more uncertain with the quicker progression of the inverted trough. Sufficient moisture will still be in place in most areas Friday, but some drying is now forecast across eastern Arizona. Shower and storm chances for Friday afternoon and evening are now more favored from Phoenix westward with the help of broad ascent associated with a south to north oriented upper level jet over California. Should also have some isolated to scattered storms across the eastern Arizona high terrain, but the drying coming out of New Mexico should limit coverage. Storm chances Saturday look to shift back to the east with another jet streak coming up from the south providing ascent more focused across central and eastern Arizona while better moisture is again seen across eastern Arizona. Near to slightly above normal monsoon moisture levels and forecast soundings for Friday and Saturday point toward a mix of storm threats from strong winds to locally heavy rainfall and possible flooding. Drier air will begin working in from the southwest starting Sunday, likely ending storm chances across most of the western deserts and considerably lowering chances elsewhere. The southwesterly drying flow will result from the subtropical high weakening while shifting south and an upper level trough becoming the dominant feature along the West Coast. This unfavorable monsoon flow pattern should persist through early next week with another high center forming to our southwest on Monday and even drier northwesterly flow spreading through the region. Minimal storm chances over the eastern Arizona high terrain are expected for Monday and Tuesday, but for now it seems the lower deserts will be dry for a few days. Eventually, model ensembles show the new high center shifting northeastward into the Four Corners area later next week which will likely bring a return to more favorable monsoon moisture flow out of the southeast and increasing storm chances. Temperatures today and Thursday should be the warmest of the week with highs across the western deserts between 109-112 degrees to 102-105 degrees in the Phoenix area. Cooling will occur by Friday and last through the weekend with forecast highs from the upper 90s in the Phoenix area to 100-105 degrees over the western deserts. Temperatures should return to near normal readings for the western deserts during the first half of next week, while the south-central Arizona deserts will likely fall just short of normal readings. && .AVIATION...Updated at 1854Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Typical diurnal wind patterns expected through most of the TAF period with speeds generally 8 kts or less. Variability at terminals this morning should become more consistently westerly by 19-20Z. Isolated storms will likely develop over the high terrain to the north and east, while the metro area remains dry with FEW to SCT clouds around 15 kft. There is a 5-10% chance distant outflows move into portions of the metro this evening, but should be weakening on approach. Shower and storm chances increase Thursday. Initially in the morning there may be a few ACCAS or virga showers passing over the area, mainly between 10-17Z. In the afternoon, isolated to scattered showers and storms are expected to develop across the region with a westward progression. Most activity may initially develop east and south of the metro before spreading into the area. Activity in the metro may begin as early as 20-21Z, but the most likely timeframe for storms is between 23-5Z. Winds may be variable and erratic in the vicinity of storms. There is a 60-70% chance for winds in excess of 30 kts and a 5-10% chance for speeds over 50 kts. CIGs Thursday afternoon and evening may fall as low as 6-7 kft. Southeast California/Southwest Arizona including KIPL and KBLH: A weak disturbance is producing an area of showers with embedded thunder near KBLH this morning. Vicinity showers are likely through the next couple hours before drifting out of the area. Isolated storms may also develop in the area later this afternoon. KIPL is expected to remain dry. Winds at KIPL will favor an east/southeast component through most of the TAF period, while winds at KBLH favor the south to southeast. A sudden wind shift accompanying an outflow boundary is a possibility during the afternoon at KBLH. Clouds will mostly remain FEW-SCT with decks as low as 10 kft at KBLH, but mostly aoa 15 kft. && .FIRE WEATHER... Friday through Tuesday: Unsettled conditions are expected late week and likely through the weekend with a couple of weather disturbances moving through the region. This should bring daily shower and storm chances across the entire area Friday and Saturday before decreasing chances from west to east Sunday into Monday. Main threats will be strong thunderstorm winds, heavy rainfall and localized flooding. Temperatures will range from near to slightly below normals the bulk of the period. Minimum afternoon humidity values will range from 25-45% through the weekend before falling back to 15-30% early next week. Overnight recovery will be mostly good to excellent in a 40-80% range. Apart from thunderstorms, winds will favor typical daily upslope/drainage patterns. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && DISCUSSION...Kuhlman AVIATION...Benedict FIRE WEATHER...Benedict/Kuhlman
Special Weather Statement National Weather Service Phoenix AZ 907 AM MST Wed Jul 28 2021 AZZ530-533-CAZ569-570-281645- Parker Valley AZ-Central La Paz AZ-Palo Verde Valley CA- Chuckwalla Valley CA- 907 AM MST Wed Jul 28 2021 ...SIGNIFICANT WEATHER ADVISORY FOR WEST CENTRAL LA PAZ AND RIVERSIDE COUNTIES UNTIL 945 AM MST/945 AM PDT/... At 907 AM MST/907 AM PDT/, Doppler radar was tracking a strong thunderstorm 9 miles west of Quartzsite, or 31 miles south of Parker, moving northwest at 15 mph. Wind gusts up to 50 mph will be possible with this storm. Locations impacted include... Blythe, Quartzsite and Ehrenberg. This includes the following highways... AZ Interstate 10 between mile markers 4 and 15. CA Route 95 between mile markers 4 and 24. LAT...LON 3370 11424 3356 11437 3373 11472 3394 11453 TIME...MOT...LOC 1607Z 126DEG 13KT 3368 11438 MP
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1010 AM MST WED JUL 28 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1215 AM FLASH FLOOD 4 NW ROOSEVELT 33.70N 111.19W
07/23/2021 GILA AZ DEPT OF HIGHWAYS
*** DELAYED REPORT *** AZDOT REPORTS A ROAD
CLOSURE DUE TO DEBRIS FROM AN OVERTOPPED
DRAINAGE CUT FEATURE DUE TO FLOODING BETWEEN
MP 246 AND 253 ON HWY. 188.
&&
GLThe Santa Ana Mts radar (KSOX), 141 km away, was scanning. The volume nearest the first event began at 20:32 UTC.
2 flash flood. Local standard time, as filed.
Officials with Joshua Tree National Park reported several inches of swiftly moving water flowing over Indian Cove Road, making the road impassable. Timing was estimated using radar. No damage or injuries were reported.
Officials with Joshua Tree National Park reported that vehicles traveling along Pinto Basin Road Between Fried Liver Wash and Turkey Flats were forced to turn around due to several inches of swiftly moving water flowing over the roadway due to running washes. No damage or injuries were reported.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2021Every state in 2021This day in weather historyWarnings in California, July 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: 977079, 977080.