In early May of 2006, I flew down to Alfonsina’s Hotel at Bahia San Luis Gonzaga in Northern Baja along with two friends, Marty and Jim. The occasion was Marty’s Bachelor party. No Vegas, no strippers, just a low-key long weekend trip to Alfonsina’s for some fishing, a few cold Pacifico’s, and some shrimp tacos. The flight down from the Bay Area in my sturdy little 1965 Cherokee 180C was relaxing, with a nice 15-20 knot tailwind, clear skies, and great visibility all the way down. The fishing was fantastic, the beer was cold, and the shrimp tacos were the best! Our weekend was exactly what we had planned.

Mission accomplished, we departed Alfonsina’s into a beautiful, windless Baja morning and arrived at Calexico (KCXL), our airport of entry a couple of hours later. After clearing US Customs and fueling up, I obtained a weather briefing for our hop home to KOAK. Our planned route took us to the west from Calexico, and around the R-2510, up the Borrego Valley, over Hemet and Riverside, through the Cajon Pass and across the High Desert past Palmdale, and over the Tehachapi Mountains. Then a straight shot up the west side of the San Joaquin Valley, over Panoche VOR (PXN) and up V301 and straight into Oakland’s Runway 28R.

As we got further into the briefing, the weather situation near the Bay Area started sounding less and less like a happy story. Conditions in Southern and Central California were just fine, and we actually had a bit of a tailwind to push us along very nicely.

Once we got within about a hundred miles of Oakland, however, conditions were forecast to deteriorate as a late season cold front pushed its way through Northern California and the Bay Area to the southeast. As our Pacific storms go, this one was not forecast to be anything special. There were no Convective SIGMETs, just the ubiquitous AIRMETs for Turbulence and Mountain Obscuration (pretty much a daily occurrence in the Bay Area), the winds aloft forecast was generally from the South at 20-25 knots, well within my personal minimums of 35 knots.

The forecast was for ceilings from 3000 ft to 5000 ft, tops at around 12,000 ft, with scattered light rain showers, freezing level was about 9,000 ft, with good visibility below the clouds. All the airports along my route, from Paso Robles up into the Bay Area were landing south or southeast, so the surface flow was consistent with the flow aloft.

When I queried the briefer as to the intensity of the areas of precipitation within the frontal band, his reply was that the Doppler radar site atop Mt. Umunhum in the Santa Cruz Mountains, about 10 miles south of San Jose International was down for maintenance. No radar data available. The surrounding sites were showing generally light precipitation, with a few isolated areas of moderate precip.

PIREPs are a significant consideration in any weather briefing, especially in the absence of any supporting hard weather data. Without local Doppler radar data, my next question was about any PIREPs in the Bay Area and along the final hour of our route. The briefer’s reply was negative. Nothing, nada, zilch.

So, my analysis was this… With the tailwind, our flight would be relatively short, 3 hours rather than 3:45. Flight conditions up until the last 45 minutes or so would be very good, with clear skies, unlimited visibility, and a tailwind to boot. Somewhere around Panoche VOR, the clouds associated with the front would begin, and we could make a determination on how to proceed into KOAK as we got closer to the Bay Area and an in-flight weather briefing. The timing would work out such that we would be arriving at KOAK about 30 minutes after the projected time of frontal passage. The forecast for our arrival was for wind from the west at 12-15 knots, scattered clouds at 3000 ft, and isolated rain showers. It sounded like a relatively benign blow-through to me.

We had a plan in place, we had plenty of options along the way, and we had a nice tailwind going home. Full of fuel and a fantastic breakfast at Rosa’s restaurant on the field at KCXL, we launched.

The first two hours of the flight home were exactly as advertised. We slid along at 8500 ft over Southern California, out north and east of LA without so much as a bump. We passed out to the west of Bakersfield, and roughly paralleled I-5 up the San Joaquin Valley. As predicted, we could see the clouds out ahead of the frontal band as we neared PXN. I went off NorCal frequency and contacted Oakland Radio for updated weather along the rest of our route and into KOAK. The briefer told me that the forecast weather was still valid. The front had just passed Oakland, and the conditions there were as forecast as well.

My immediate concern was the conditions along V301, over the Diablo Range between San Luis Reservoir and SUNOL intersection, to the south and east of Livermore on the arrival into Oakland. Again, I asked if the Doppler radar had come back up. “Negative,” was his reply. The surrounding sites were still showing just light precip. “Any ride reports on V301 at our altitude over the mountains?” I asked. “No complaints,” he told me.

When I came back on NorCal frequency, I asked for a pop-up IFR Clearance into KOAK for the ILS. I was cleared Present Position, V301, SUNOL, direct, maintain 8000, and expect the ILS28R. Pretty routine stuff. I figured it would be a good opportunity to get some actual IMC time and an ILS approach to 28R. Again, I asked NorCal if there were any ride reports over the mountains. “No complaints,” replied the controller.

We went into the clouds about over PXN VOR. No big deal. We were just bumping along V301, in and out of the clouds at first, then solid IMC. In the clouds it was just light chop, and my little Piper pretty much just flew herself, even without an autopilot. For about 15 minutes it went along like that, until we were near KARNN intersection.

Then the world suddenly went mad.

The airplane started shaking and vibrating so violently that the instrument panel was a blur. My first thought was that we had lost part of a prop and the imbalance was causing the plane to shake itself apart. I pretty quickly discarded that thought, and realized we had just penetrated an imbedded thunderstorm. So this was what the inside of a thunderstorm felt like. I didn’t like it.

With the Diablo Range mountains below me ranging anywhere from 2500 to 4000 feet, I knew safety lay to my north, over the Central Valley. I can’t honestly say I remember declaring an emergency or telling NorCal what my intentions were. I was pretty busy just trying to keep the airplane under control. I must have declared an emergency though, because I heard NorCal Approach tell me that I was cleared to descend to 6000 feet and turn right heading 360.

I remember reducing power so that we were just below Va, or at least averaging somewhere in that neighborhood. It was also extremely difficult to maintain anything resembling a stabilized descent since my vertical speed was oscillating wildly between +1000 and -1000 ft./min., oftentimes within a few seconds. Trying to maintain a heading within 30 degrees was next to impossible with the wild rolls that the turbulence was causing my little airplane to make.

It was purely survival mode. We were in a solid gray hell, and the Devil was having his way with us. Whenever I would manage to lose some altitude, we would get knocked back up 500 ft. by a tremendous updraft. Every time I would get the heading stabilized somewhere near 360, we would be swatted violently to the left or right and I would have to fight my way back to that heading.

After what seemed like an hour (it was probably no more than several minutes), we reached 6000 feet, but no joy. We were still in solid IMC, and we were still getting battered about mercilessly. I told NorCal that we were still in trouble, and needed to descend to 4000 feet. I was cleared down to 4000 feet, and they gave me a right turn to heading 040 to get me over lower terrain quicker. NorCal told me that the old abandoned NAS Crows Landing airstrip was 12 o’clock and about six miles.

As I descended out of 6000 feet, the turbulence seemed to gradually decrease, and I was able to maintain control quite a bit better. We would still get rocked periodically, but in general the turbulence was decreasing in severity as I descended.

Finally, at about 5000 feet, we came out of the bottom of a very solid black cloud base with Crows Landing directly ahead of us, bathed in brilliant sunlight. I asked my passengers if they were OK, and took stock of the airplane. We seemed to have both wings still attached, the engine was running smoothly, and we were in the clear. I was so relieved to be out of that thunderstorm, I completely forgot to inform NorCal that we were OK. There was complete silence on frequency. It seemed like everyone on frequency was holding their breath. The controller finally came on and asked if we were all right. I told him we appeared to be in one piece, and that we would cancel IFR, and proceed to Oakland VFR.

All at once, everyone on frequency was asking for deviations. Airliners on the EMZOH Arrival to Oakland that were descending out of the flight levels in this area needed to deviate around a massive thunderstorm that had billowed up to their altitude in a matter of minutes. We proceeded northbound until we were several miles north of Interstate 5, then turned back to the northwest toward Oakland. It was at that point we got our first look at the monster that we had just flown out of. It was huge. It was dark, and it was dropping lightning and massive precipitation. I couldn’t believe we had been inside that thing and lived.

The rest of the flight home was a big non-event. We had a little turbulence and a few scattered showers as we made our way up the Central Valley, over the Altamont pass, past Livermore, and on into KOAK.

After we landed, I did a thorough post-flight inspection of the airplane to see if anything had been damaged in flight. I could not find one single wrinkle. Quite the testament to the Piper engineers and designers.

When I got home, I got on the phone to FSS to ask the big question… What the hell had just happened? I actually got a very talented briefer on the line who was able to do a little detective work on conditions in the area at the time. It turns out that just prior to the time we were in distress, Monterey, Watsonville, and Salinas all experienced an increase in surface wind velocity, along with an increase in temperature and dewpoint just before the front passed over the area.

A pulse of warm moist air came ashore from over Monterey Bay, accelerated through Hecker Pass, a low gap in the Santa Cruz Mountains separating the Monterey Bay Coastal Plain from the southern Santa Clara Valley. That pulse of moisture-laden air smacked up against the Diablo Range mountains on the southwestern side with a lot of energy. So we had a warm, moist air mass moving at high velocity, unstable cold air aloft from the passage of the cold front, and a lifting mechanism. Sounded like a recipe for a thunderstorm to me.

Since that flight, I’ve become a lot cagier about situations like this. I will no longer accept a clearance over the Diablo Range with any kind of weather, opting instead to stay over the Central Valley at a lower altitude until we reach the Altamont Pass area, where the hills are much lower, before we turn towards Oakland for the approach.

I use this incident in my IFR Instruction as well. I assign my instrument students cross-country flights that could potentially take us over this area at times of questionable weather, then discuss strategies to avoid such a situation by planning a route that circumvents the area. Once bitten, twice shy.

Nowadays, whenever I ask for a ride report, and the controller says “No complaints,” I just kind of smirk, and say to myself, “Yeah, right…”