I'm interested in obtaining observations from anyone else who experienced the Saturday morning thunderstorms of 9/24/11 in the Sierra. The reason is that I was out three days from a definite forecast, and had to make decisions in the backcountry based on poorly described NWS dynamics extending into the weekend. I am attempting to come to terms with the forecasted conditions versus the actual weather events.

Based on personal observation and experience, I had surmised a shortwave with a vigorous cold front had snuck in earlier than forecast on the back of a Sunday forecasted trough digging in from the Gulf of Alaska, while simultaneously a cutoff low from of Santa Barbara became absorbed into and deepened the general dynamics, resulting perhaps in a significant first autumn snow event. This was incorrect! Saturday's wild weather turned out to be solely the result of the quickly traveling cutoff low. Sorry if the meteorology seems a bit obtuse. In the interest of learning from the experience, please include the following points, if possible, and feel free to add any other experiences. I'll start.

1) LOCATION: Little Five Lakes to the east of the Great Western Divide.
2) ELEVATION: 10,400'
3) TIMING: There was actually lightning and thunder all night Friday and early Saturday morning all around my camp, but activity ramped up about 9:00 AM and persisted until about 3:00 PM.
4) EVENT DESCRIPTION: Temperature, Wind, Precipitation, etc.

Three separate events occurred:

Morning, Little Five Lakes

The first at 9AM lasted about an hour and a half and consisted of heavy rain, hail, snow above 11K, and erratic winds, blowing (not so much gusting) to what I estimated may have been up to 60 mph. The temperature fell about 20 degrees to 40F. I was just about to strike my tent when the weather closed in, and so sat out the fireworks in relative shelter, bridging the fabric to buress the tent during the longer blows. At first rounds end, the Kaweah Peaks were newly plastered with snow.

Kaweah Peaks, New Snow

After a 25 minute respite, a second round began at around 11AM with the same violent weather experienced as in the first, although of a somewhat shorter one hour duration. The second lull beginning around noon lasted about and hour. Having already made the decision, because of the severity of the second event, I packed up as quickly as possible to leave the area for lower elevations, before the next round. At 1:45PM I ascended a snow covered Black Rock Pass in a blizzard (not my original route of intention) in order to make it out west to Mineral King during the third, albeit still less violent event.

Blizzard Little Five Lakes Basin

By 3PM, I had topped out on Black Rock and the weather began to clear rapidly with no visible weather to the west. The temperature had risen to near 60F at 11,6K elevation.

Sawtooth Peak and Spring Lake


What did you experience?

1) LOCATION: West Walker River south of Sonora Pass (en route to Tower Peak)
2) ELEVATION: 8,275' on Saturday, up to 11,755' on Sunday
3) TIMING: Sunny, warm, and calm on Saturday morning. Around 3:00 PM clouds rolled in and rained lightly for about 90 minutes. Could hear occasional thunder in the distance but never saw any lightning. After 5:00 PM Saturday remained cloudy but calm until nightfall, calm throughout the night (did not bother sleeping in a tent). Sunday was sunny in the morning, 50-80% cloud cover beginning midday. Cold and windy on the ridgetops, but not an issue- never so strong that a gust would come close to pushing you around. Felt a few drops on Sunday afternoon for about 5 minutes, barely enough to notice. Never much wind at all except as mentioned on the highest ridges.
4) EVENT DESCRIPTION: See above.

From another thread...

The Chief wrote:The fact is regardless what the NOAA/NWS computer model probability forecasts as far as %'s, isolated intense TSers happen regardless their potential forecast %'s.

20-30% last weekend and I still came the closest I ever have in over 40 years to getting nailed by lightning (10' or so feet away) in a heinous lightning storm that brewed up and swept my vicinity very quickly. Myself and my clients hunkered down, allowed the TS squall move off to the north and we high tailed the fk from our location immediately. Oh, several inches of graupel in less than three minutes overwhelmed us as well leaving a decent that was like moving down in a UPS packing store. Five other parties pretty much ran for their lives as well. Bad Juju!! Most likely the exact same cell that the OPist here experienced.

Three of my friends were a few hundred feet shy of the notch on Whintey when the storm hit. I saw some amazing pictures. Pretty crazy stuff!!

1) LOCATION: North Lakes Campground (9,300') to Mount Tom Ross (13,253')
2) ELEVATION: 12,880' at Lamarck Col when storm hit
3) TIMING: Driving north from LA Friday night saw lightning to the northwest and experienced a light rainshower just north of Mojave. Arrived at Four Jeffrey campground approximately 0100 Saturday to another couple of light showers. Awoke 0500 to partly cloudy skies. Ascended to Lamarck Col from North Lakes Campground from around 0645 to 1130 under partly to mostly cloudy skies. The oncoming weather was obscured by the ridgeline as we approached from the east. When we arrived at the col, we could see the snow falling on Mounts Darwin and Mendel. Took a couple minutes to put on hard shell and graupel began to fall. Since there was no thunder we began the traverse along the ridge. I stopped to check the map and my partner noticed my trekking poles lashed to my pack were clicking, like an electrical charge, so we bailed back over the col. Experienced graupel to approxmately 12,200' and then solid snowfall to approximately 11,200. Below timberline the winds would periodically gust and the skies were threatening but we received no further precipitation. Arrived at North Lakes around 1430. The rmainder of the afternoon was warm and mostly sunny.

Sunday morning at Convict Lake was partly cloudy and cool with some clouds rolling in from the west but no precipitation fell.

Sunday afternoon at the Patriarch Grove (11,300') was mostly cloudy and cool. Around 1500, low clouds with virga began to roll in from the west and the temperature dropped 10-15 degrees F but no precipitaton reached the ground. No thunder. Over the next 1.5 hours, the skies lightened and the temperature rebounded.

4) EVENT DESCRIPTION: See above.

I got turned around on Sunday 9/25 but I guess that's the wrong day for your observations

I've usually found the NWS forecasts pretty good, though I've never relied on one more than a day or two old. Here is last weekend's forecast, issued Friday afternoon:

ISSUED 301 PM PDT FRI SEP 23 2011/
A FEW SHOWERS DEVELOPING OVER THE SIERRA NEVADA THIS AFTERNOON.
OTHERWISE MOST OF THE SHOWER ACTIVITY HAS REMAINED TOWARDS SANTA
BARBARA AND SAN LOUIS OBISPO COUNTIES. THINK THE CONVECTIVE THREAT
FOR THUNDERSTORMS WILL CONTINUE OVER THE SOUTH HALF OF THE
DISTRICT INTO THE EARLY EVENING. AN UPPER LOW OFF POINT CONCEPTION
WILL LIFT NORTHWARD OFF THE CENTRAL COAST THIS EVENING TAKING THE
BEST DYNAMIC FORCING TOWARDS CENTRAL VALLEY AND YOSEMITE AREA
TONIGHT. MODELS PROG THE UPPER LOW TO WEAKEN BUT PUSH EAST OVER
CENTRAL CALIFORNIA SATURDAY. INSTABILITY DECREASES TOWARDS THE
COAST BUT CONDITIONS REMAIN UNSTABLE OVER THE SIERRA FOR A
CONTINUED THREAT OF THUNDER.

Slept Friday night just above Gallison Lake, ~11450+ ft. No precip at night but sky did cloud up a couple of times.

Based on forecast and persisting afternoon cloud cover and showers the few days before, got up at dawn and summited Simmons Pk at 9:30 (likely my earliest summit ever). Took our time descending, able to sumbathe between noon and 1 in camp while cloudwatching. Then three waves of precip, the first starting with graupel/hail. Didn't really clear until after dark, and sky had some cloud most of the night. Still cloudy all through Sunday morning on the way back to Tuolumne, but dry--cleared between noon and 2.

1) LOCATION: PCT South of Ebbets Pass to Highland Peak
2) ELEVATION: 10,900'
3) TIMING: Clear in the Ebbetts pass area until about noon- the initial storm front appeared to pass through the Sonora Pass area and parked itself over the 395 corridor. Heard thunder from that storm but no lightning. A second system headed north into the Ebbets Pass area a few hours later (~2-3pm) and dumped a fair amount of rain on the pass. (To the point were there were a bunch of very unhappy soaked motorcyclists pulled over and standing waiting for the storm to pass)
4) EVENT DESCRIPTION: Thunder, lightning, Freezing rain that shifted to a non-freezing downpour

http://www.fedak.net/albums/HighlandPeak.html