A strong high pressure center over the Pacific Northwest pulled in moisture from the east which produced thunderstorms over the Sierra Nevada during the afternoon of June 29. Although the thunderstorms on the previous day were mainly dry with very little rainfall, the moisture surge the following day was deeper and as a result some of the thunderstorms produced locally heavy rainfall, damaging…
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The episode as NWS HNX wrote it up.
A strong high pressure center over the Pacific Northwest pulled in moisture from the east which produced thunderstorms over the Sierra Nevada during the afternoon of June 29. Although the thunderstorms on the previous day were mainly dry with very little rainfall, the moisture surge the following day was deeper and as a result some of the thunderstorms produced locally heavy rainfall, damaging outflow winds and small hail during the afternoon and early evening hours of June 29.
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 Hanford, CA wrote its last area forecast discussion before the first event at Jun 29, 12:53 PM PST, 1 hour 7 minutes earlier.
Area Forecast Discussion National Weather Service Hanford CA 153 PM PDT Tue Jun 29 2021 .SYNOPSIS... Hot temperatures will continue through mid-week, with slight cooling by the end of the week. Isolated to scattered showers and thunderstorms are expected over the mountains and desert through Wednesday. Isolated storms will continue over the Sierra Nevada each afternoon through the end of the week. && .DISCUSSION... Convection has started earlier today across the sierra and Mojave Desert. A surge of moisture moved in from the north overnight with an area of showers pushing through the Indians Wells Valley and south sierra this morning. The upstream sounding from Reno shows moisture is at mid levels of the atmosphere with dry lower levels. So there is a potential for dry thunderstorms through the evening. Think any storms on Wednesday will be wetter and provide more localize rain as models show humidity levels increasing at lower levels. Drier air will be moving onshore through south CA Wednesday and should decrease the potential for convective storms towards the Tehachapi Mountains. However the threat of convective storms will continue over the sierra though the end of the week as the axis of the moisture remains along and east of the sierra while the drier air remains towards the coast. A low forming off the north CA coast will provide a stronger south flow and finally send the moisture northward Thursday night. This will decrease and limit the threat of convective storms towards Yosemite Friday. Little change in temperatures tonight as the ridge remains anchored over the PacNW. Temperatures should remain warm over the thermal belts near the foothills perhaps around 80 degrees. Models prog for the ridge to start shifting east Wednesday. This will bring a slight cooling towards the north sectors but most locations may end up in triple digits especially the south valley. Higher resolution models show a good gradient onshore wind setting up during the early evening Wednesday. There could be some good cooling Wednesday night due to the cooler marine air. Heat index values lower into the moderate category over much of the district Wednesday perhaps due to the cooler overnight lows Thursday morning. So will not extend the heat warning. Little change in temperatures through the weekend but should remain a bit above normal levels. && .AVIATION... Local MVFR/IFR over the mountains due to isolated thunderstorms through 06Z Wednesday. Otherwise, VFR conditions will prevail across the central CA interior for at least the next 24 hours. && .AIR QUALITY ISSUES... On Tuesday June 29 2021... Unhealthy for sensitive groups in Kern County and Sequoia National Park and Forest. Further information is available at Valleyair.org && .CERTAINTY... The level of certainty for days 1 and 2 is medium. The level of certainty for days 3 through 7 is medium. Certainty levels include low...medium...and high. Please visit www.weather.gov/hnx/certainty.html for additional information an/or to provide feedback. && .HNX WATCHES/WARNINGS/ADVISORIES... Excessive Heat Warning until 8 PM PDT this evening for CAZ179- 182>189-198-199. Red Flag Warning until 8 PM PDT this evening for CAZ299-595>597. Red Flag Warning until 8 PM PDT this evening for CAZ592>594. && public...MV aviation....DS weather.gov/hanford
Special Weather Statement
National Weather Service San Joaquin Valley CA
214 PM PDT Tue Jun 29 2021
CAZ192-292200-
Central Sierra CA-
214 PM PDT Tue Jun 29 2021
...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN MARIPOSA...
SOUTHEASTERN TUOLUMNE AND NORTHERN MADERA COUNTIES UNTIL 300 PM
PDT...
At 213 PM PDT, Doppler radar was tracking a strong thunderstorm near
Tioga Pass, or 13 miles southwest of Lee Vining, moving south at 20
mph.
Wind gusts up to 50 mph will be possible with this storm.
Locations impacted include...
Tioga Pass, Merced Lake High Sierra Camp, Vogelsang High Sierra Camp,
Tuolumne High Sierra Camp, Sunrise High Sierra Camp, Tuolumne
Meadows, Glen Aulin High Sierra Camp, Merced Lake Ranger Station,
Tuolumne Meadows Visitor Center, Tenaya Lake, Tuolumne Meadows
Campground and Dana Meadows.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.
&&
LAT...LON 3793 11927 3791 11925 3776 11925 3774 11927
3773 11925 3764 11925 3768 11949 3798 11943
TIME...MOT...LOC 2113Z 011DEG 18KT 3785 11932
DSThe national radar mosaic for the moment the first event began.
1 heavy rain, 1 thunderstorm wind. Local standard time, as filed.
A thunderstorm produced heavy rain at Tuolumne Meadows with 1.25 measured at the ranger station between 1500 and 1700 PDT. The storm also produced pea sized hail and flooded some tents at the Tuolumne Meadows Campground.
The Upper Providence remote weather station estimated a wind gust of 60 mph from a thunderstorm.
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, June 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: 957125, 957126.