5 with MLCAPE values near 1000 J/KG, thunderstorm activity developed across the Mohave Desert during the early afternoon hours. An isolated strong thunderstorm developed over the higher terrain area of Joshua Tree National Park, where it remained anchored and dumped over an inch of rain in less than one hour, enough rainfall in a short time span to cause road closures due to flooding.
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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.
In an environment characterized by PWAT values of around 1.5 with MLCAPE values near 1000 J/KG, thunderstorm activity developed across the Mohave Desert during the early afternoon hours. An isolated strong thunderstorm developed over the higher terrain area of Joshua Tree National Park, where it remained anchored and dumped over an inch of rain in less than one hour, enough rainfall in a short time span to cause road closures due to flooding.
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 23, 12:44 PM PST, 1 hour 31 minutes earlier.
Area Forecast Discussion National Weather Service Phoenix AZ 144 PM MST Tue Jul 23 2024 .SYNOPSIS... Daily thunderstorm activity is expected to continue through the rest of the week, with the highest chances across the AZ higher terrain areas. Storm chances will still exist across the lower deserts, with large daily fluctuations in coverage. Drier conditions are expected during the upcoming weekend. Temperatures through the next several days will remain above normal. && .DISCUSSION... The latest objective analysis depicts the center of the subtropical ridge situated over southern NV with most of the region entrenched under northeasterly flow aloft. Widely scattered and storms have already started develop along the vicinity of the Mogollon Rim. The activity through the afternoon will be steered southwestward into portions of Yavapai, Gila, and Mohave counties and eventually into the lower deserts of south-central and southwest AZ. The main question is gonna be whether or not these storms survive their trip into the lower deserts and this aspect of the forecast is not clear cut as the latest Hi-res model guidance continues to show widely varying solutions. Everything will be dependent on whether or not the storms that initially develop over the High Country can spark a deep enough outflow boundary or any sort of outflow collisions to spark new storm development across the lower deserts. Another area in which thunderstorm activity has already developed has been across western portions of Joshua Tree National Park as well as across the Peninsular Range of the northern Baja Peninsula and San Diego Mountains, which could instigate some new development across western Imperial County later on this afternoon. There is also some signal of potential new thunderstorm activity developing in portions of Riverside County from outflow collisions from activity from western AZ and the Mohave desert as well from the San Diego Mountains and western Imperial County. The main hazard with these storms as they mature will be the potential for strong gusty winds with latest HREF indicating a 30-70% chance of gusts of 35+ mph across a wide area, with a 5% chance of 58+ mph gusts, especially across western AZ and the Mohave Desert Region. With the strong winds will also be the potential for areas of blowing dust to materialize in the dust prone areas. Locally heavy rainfall will also be possible, especially near the vicinity of Joshua Tree National Park. Heading into the middle to latter half of the week, as a trough impinges across the Pacific Northwest, the subtropical ridge is expected to be displaced very slightly southeastward into western AZ while strengthening slightly as 500 mb height fields increase to between 597-600dm. The overall steering flow is not expected to change that much with the mid-level flow still remaining out of the east to northeast. The latest hi-res model guidance indicates a much more active day for convection across eastern and southeastern AZ on Wednesday. Not much thunderstorm activity is being depicted across the south-central AZ lower deserts Wednesday evening, however, if there are multiple outflow collisions, then storm chances will indeed go up. A strong outflow boundary originating from the activity across eastern and southeastern AZ is likely to migrate its way northwestward through south-central AZ and could potentially result in blowing dust issues, especially across Pinal County. What the outflows will likely do is increase the low-level moisture and setup for a better storm environment for Thursday. Guidance for the past several iterations has been hinting on the potential for better storm coverage across the south-central AZ lower deserts, including the Greater Phoenix area, for Thursday. A robust shortwave that develops along the eastern periphery of the ridge is being indicated by guidance to move in, providing larger scale forcing for ascent. In addition, with the better moisture likely to be in place, forecast soundings for Phoenix indicate MLCAPE values of 1000-1500 J/KG. Therefore, the combination of the good thermodynamic environment in addition to the larger scale forcing for ascent from the shortwave energy should be sufficient for more robust storm activity to materialize Thursday evening across the south-central AZ lower deserts. Ensemble guidance continues to be consistent in indicating an upper- level trough progressing into the Great Basin Region through the weekend. This will cause the subtropical ridge to be displaced further southward towards the international border while also weakening in the process. This pattern shift will result in some form of a drier westerly flow to settle in, dropping moisture levels. As a result, a decrease in monsoonal thunderstorm activity is likely, with activity mostly confined to far eastern and southeast AZ for Saturday and Sunday. By early next week, the ensembles indicate that the subtropical ridge will quickly rebound and move back into the Four Corners region. At the same time, there are indications from both the GFS and ECMWF deterministic model solutions of a potent inverted trough moving into the region from Mexico. If the model guidance is correct with the depiction of the inverted trough and with moisture increasing, then a more active thunderstorm pattern is likely to setup. High temperatures today will continue to remain similar to yesterday with highs between 108-113 degrees across the lower deserts. As the subtropical ridge strengthens Wednesday and Thursday, hotter temperatures can be expected with highs of 109-114 degrees across the AZ lower deserts to between 115-118 degrees across southeast CA. An Excessive Heat Warning is in effect for areas along the Colorado River Valley westward through all of southeast CA through Friday as the combination of the hotter temperatures along with dewpoints in the mid 60s to mid 70s will cause heat indices to approach or in some cases exceeding 120 degrees, making for oppressive conditions. Heading into the weekend, as the subtropical ridge weakens, temperatures will be cooling off with highs across many of the lower desert communities likely staying near to just below 110 degrees. && .AVIATION...Updated at 1832Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation weather concerns during the TAF period will be the potential for isolated showers and thunderstorms in the Phoenix area along with gusty erratic outflow winds later this afternoon into the evening. There is still a good deal of uncertainty with regards to how convective development will evolve as well as the timing and magnitude of outflows into the Phoenix metro. Current thinking is that at least some isolated shower and thunderstorm activity will survive into the metro if a strong enough outflow boundary is present. Have kept mention of VCTS in the TAFs for KSDL and KDVT where greater thunderstorm potential will exist and VCSH for KPHX. Outflows will favor a NE to NW direction with about a 60-70% chance for outflow winds to exceed 30 kts. Exact timing of outflows remains uncertain, but the best timing currently is between 00-03Z. Winds will switch back to the east overnight before an early switch to the west is expected Wednesday morning. There will be fluctuating mid and high clouds throughout the period with bases down to around 10 kft with convection. Southeast California/Southwest Arizona including KIPL and KBLH: The primary aviation weather concerns through the next 24 hours will be the threat for gusty outflow winds along with isolated showers and thunderstorms. Guidance suggest that thunderstorms will develop near southwest Imperial County and send an outflow traveling toward the E-NE this afternoon. This outflow will have the potential to generate some blowing dust along with isolated shower and thunderstorm development. There is about a 20-30% chance for outflow winds to exceed 30 kts and up to a 10% chance for winds to exceed 50 kts at KIPL. At KBLH, some isolated thunderstorm development will be possible this afternoon before a strong outflow pushes through from the NE this evening, though an outflow from the SW could collide with the NE boundary near KBLH. Some blowing dust will be possible along with an isolated shower or thunderstorm at KBLH with probabilities for gusts in excess of 30 kts up to 30-50%. Winds outside of any thunderstorm development will be E-SE at KIPL and S at KBLH. Mid and high cloud coverage will fluctuate with convective development with bases down to around 10 kft. && .FIRE WEATHER... Widely scattered afternoon and evening thunderstorms will be common over higher terrain locations of eastern districts through the majority of the week with storms occasionally propagating into lower elevations. While only a few areas are expected to receive beneficial wetting rainfall, the main impacts from these storms will be strong, gusty outflow winds which could affect any ongoing wildfires and the possibility of new starts due to lightning. Winds outside of thunderstorms will generally exhibit typical afternoon upslope tendencies with gusts commonly around 20 to 25 mph. Otherwise, minimum afternoon humidity levels will mostly fall in a 20-35% range with a potential for modest drying towards the end of the week and weekend. Overnight recovery should be highly variable from 30-40% in lower elevations to 40-80% in higher terrain of eastern districts. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Friday for AZZ530-532. CA...Excessive Heat Warning until 8 PM PDT Friday for CAZ560>570. && DISCUSSION...Lojero AVIATION...Smith FIRE WEATHER...Salerno
Special Weather Statement
National Weather Service Phoenix AZ
1209 PM PDT Tue Jul 23 2024
CAZ560-231945-
Joshua Tree NP West CA-
1209 PM PDT Tue Jul 23 2024
...A STRONG THUNDERSTORM WILL IMPACT SAN BERNARDINO AND RIVERSIDE
COUNTIES THROUGH 1245 PM PDT...
At 1209 PM PDT, Doppler radar was tracking a strong thunderstorm near
Twentynine Palms. This thunderstorm was nearly stationary.
HAZARD...Wind gusts up to 40 mph.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects.
This storm will remain over mainly rural areas of San Bernardino and
Riverside Counties.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Persons in campgrounds should consider seeking sturdy shelter until
this storm passes.
&&
LAT...LON 3408 11627 3412 11626 3412 11606 3408 11603
3407 11599 3404 11601 3403 11598 3400 11597
3396 11624 3408 11631
TIME...MOT...LOC 1909Z 157DEG 4KT 3409 11615
MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH
INSSpecial Weather Statement
National Weather Service Phoenix AZ
1243 PM PDT Tue Jul 23 2024
CAZ560-232030-
Joshua Tree NP West CA-
1243 PM PDT Tue Jul 23 2024
...A STRONG THUNDERSTORM WILL IMPACT SAN BERNARDINO AND RIVERSIDE
COUNTIES THROUGH 130 PM PDT...
At 1243 PM PDT, Doppler radar was tracking a strong thunderstorm near
Twentynine Palms, moving northwest at 10 mph.
HAZARD...Wind gusts up to 50 mph.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects.
Locations impacted include...
Lost Horse-Keys Village.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Persons in campgrounds should consider seeking sturdy shelter until
this storm passes.
&&
LAT...LON 3408 11631 3408 11627 3412 11626 3412 11606
3408 11603 3407 11600 3404 11601 3403 11598
3397 11593 3392 11624
TIME...MOT...LOC 1943Z 141DEG 8KT 3409 11616
MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH
INSPreliminary Local Storm Report
National Weather Service Phoenix AZ
225 PM MST Tue Jul 23 2024
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0215 PM Flash Flood 6 NNE JTNP-Lost Horse R 34.09N 116.16W
07/23/2024 San Bernardino CA Park/Forest Srvc
Roads along the Indian Cove Campground Site
closed due to flooding.
&&Special Weather Statement
National Weather Service Phoenix AZ
227 PM PDT Tue Jul 23 2024
CAZ564-568-570-232215-
Chuckwalla Mountains CA-Chuckwalla Valley CA-Chiriaco Summit CA-
227 PM PDT Tue Jul 23 2024
...A STRONG THUNDERSTORM WILL IMPACT RIVERSIDE COUNTY THROUGH 315 PM
PDT...
At 227 PM PDT, Doppler radar was tracking a strong thunderstorm 8
miles southeast of Desert Center, moving northwest at 5 mph.
HAZARD...Wind gusts up to 50 mph.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects.
Locations impacted include...
Desert Center.
This includes the following highways...
CA Interstate 10 between mile markers 97 and 116.
CA Route 177 between mile markers 1 and 6.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
&&
LAT...LON 3359 11516 3350 11536 3369 11556 3379 11529
TIME...MOT...LOC 2127Z 148DEG 6KT 3362 11532
MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH
INSSpecial Weather Statement
National Weather Service Phoenix AZ
311 PM PDT Tue Jul 23 2024
CAZ564-570-232245-
Chuckwalla Mountains CA-Chuckwalla Valley CA-
311 PM PDT Tue Jul 23 2024
...A STRONG THUNDERSTORM WILL IMPACT NORTHEASTERN IMPERIAL AND
RIVERSIDE COUNTIES THROUGH 345 PM PDT...
At 310 PM PDT, Doppler radar was tracking a strong thunderstorm 18
miles southeast of Desert Center. This thunderstorm was nearly
stationary.
Strong, gusty winds will be capable of producing areas of blowing
dust with reduced visibilities below 5 miles.
HAZARD...Wind gusts up to 50 mph and pea size hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor damage to outdoor objects is
possible.
This storm will remain over mainly rural areas of northeastern
Imperial and Riverside Counties.
This includes CA Interstate 10 between mile markers 118 and 125.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 3351 11501 3340 11520 3357 11540 3371 11509
TIME...MOT...LOC 2210Z 148DEG 3KT 3353 11515
MAX HAIL SIZE...0.25 IN
MAX WIND GUST...50 MPH
SDBThe Santa Ana Mts radar (KSOX), 139 km away, was scanning. The volume nearest the first event began at 22:14 UTC.
1 flash flood. Local standard time, as filed.
Roads along the Indian Cove Campground Site in Joshua Tree National Park closed due to flooding. No damages nor injuries were reported.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2024Every state in 2024This day in weather historyWarnings in California, July 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: 1202283.