Increased monsoonal moisture in Southern California resulted in thunderstorms across the San Bernardino Mountains. These storms produced cloud-to-ground lightning, which caused a brush fire near Lake Arrowhead.
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The episode as NWS SGX wrote it up.
Increased monsoonal moisture in Southern California resulted in thunderstorms across the San Bernardino Mountains. These storms produced cloud-to-ground lightning, which caused a brush fire near Lake Arrowhead. Lightning also struck a tree and caught it on fire in Fawnskin.
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 San Diego, CA wrote its last area forecast discussion before the first event at Jul 29, 11:40 AM PST, 3 hours 20 minutes earlier.
Area Forecast Discussion National Weather Service San Diego CA 1240 PM PDT Sun Jul 29 2018 .SYNOPSIS... Monsoonal flow will bring warm and humid weather tonight and Monday with scattered afternoon and evening thunderstorms over the mountains. Some of these storms may drift west into the valleys this evening and perhaps into the coastal areas tonight. This warm, humid weather pattern will remain in place through most of the week with a chance for afternoon thunderstorms over the mountains each day. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Surface convergence boundaries have set up over the mountains this afternoon between the afternoon sea breeze west of the mountains and the easterly winds over the deserts. Showers formed over the San Bernardino Mountains south of Big Bear around noon. Sounding forecasts over the mountains show moisture in the 700-200 mb layer (not quite saturated), and a dry subcloud layer below. CAPE of 1000-1500 J/kg is fcst over the mtns today so scattered convection is possible. Easterly steering winds in the 700-400 (10- 20 kft layer) may push some cells the foothills or eastern valleys. Above 400 mb (20 kft) the winds aloft shift abruptly south- southwest, so the storms over the San Bernardino Mountains may drift north over the High Desert. DCAPE is forecast around 1000 J/kg, increasing the threat for gusty downdraft winds in storms that form. There is also a flash flood potential with any storms that anchor to terrain. The visible satellite loop showed mid level clouds over Imperial County drifting west in the easterly midlevel monsoonal flow. Farther east over the Lower Colorado River Valley and the Sonoran Desert is an easterly wave that will move across Southern California tonight. This feature will continue the threat for convective cells tonight, some of which may drift west over the valley and coastal areas. This moist easterly flow raised the precipitable water to 1.69" on the 12Z NKX sounding, up from 1.20" Saturday evening. Farther east at Yuma the PW was 1.86". Satellite derived PW's central Imperial County showed a PW of 2.03" at 1745Z. This flow pattern doesn't change much through Wednesday, so there will be plenty of moisture available for diurnal convection each afternoon through Wednesday. The big picture is for a continued warm, humid and somewhat unstable airmass to be in place through midweek. Wednesday through Friday: The subtropical high over the southern Nevada/northern AZ gradually drifts south, suppressing the monsoon flow somewhat farther south into Mexico. Not quite sure if it will completely eliminate the thunderstorm chances over the mountains, but they would less widespread and more isolated. Temperatures will average close to their seasonal norms for early August. && .AVIATION... 291920Z...Coast/Valleys...SCT-BKN clouds at or abv 10000 ft MSL this afternoon and evening, with a slight chance of a showers or thunderstorms. Low clouds could again develop 06Z-09Z Monday with bases 800-1200 feet MSL and tops to 1600 ft MSL. Ceiling impacts at coastal TAF sites is likely between 09Z and 16Z Mon but timing is uncertain. Mountains/Deserts...SCT-BKN clouds at or abv 10000 ft MSL. Isolated to scattered thunderstorms are expected, especially over the mountains this afternoon. Locally strong updrafts and downdrafts will be possible near thunderstorms, along with surface wind gusts in excess of 30 KT. && .MARINE... There is a slight chance of thunderstorms this afternoon into this evening. Otherwise, no hazardous marine weather is expected through Thursday. && .BEACHES... There is a low risk of lightning at the San Diego County beaches this afternoon and evening as a few thunderstorms could move in from the east. && .SKYWARN... Skywarn activation may be needed today. It could be an active afternoon/evening provided we get enough heating in the mts. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && PUBLIC...Moede AVIATION/MARINE/BEACHES...PG
The Santa Ana Mts radar (KSOX), 66 km away, was scanning. The volume nearest the first event began at 23:01 UTC.
2 lightning. Local standard time, as filed.
Two cloud-to-ground strikes occurred outside of a rain shaft. Highway Patrol reported brush fire start just west of Lake Arrowhead. Other strikes were detected just to the east and also outside of the main rain shaft near Big Bear Lake.
A spotter reported a tree engulfed in flames from a lightning strike on Delamar Mountain Road in Fawnskin.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2018Every state in 2018This day in weather historyWarnings in California, July 2018
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: 776675, 776676.