When thunderstorms get in your way (in flight)

On March 22, I went up for some practice instrument flying with a fellow instrument-rated pilot. We headed up to McMinnville (KMMV), about a 30-minute flight. There were a few puffy clouds scattered around, but (somewhat disappointingly) nothing directly in our path, so Ryan put on his foggles and I served as the safety pilot. I watched for traffic, kept an eye on the scattered clouds, and enjoyed the view, while Ryan had to stare at the instruments and miss all the scenery.

Here’s my view of some puffy clouds away to the west (Ryan flies from the right seat):

As we flew further north, I spotted this less friendly looking cloud with vertical development and active rain. I kept an eye on it, but we were flying well to the east so it wasn’t an immediate concern.

We reached McMinnville (which was clear) and Ryan flew two approaches under the hood while I continued spotting other planes and monitoring clouds to the south and west of the airport. Originally we were going to switch so I could also fly an approach, but it seemed to me that the weather was closing in a bit so we decided to head back to Corvallis. As we returned, Ryan got to fly us into this little cloud (isn’t it stunning?) and then we were clear again.

I took the controls (and the comm), lowered my foggles, and we were cleared back to Corvallis. Now Ryan was scouting for traffic and clouds. At one point he said we’d gotten back in some clouds, so I got to flip up my foggles and enjoy seeing clouds in front of the plane’s nose (I bet that sight never gets old!). Then I was back to staring at the instruments. This was the first time I’d used this plane’s autopilot, and it was a good chance to get familiar with its operation.

After a bit, ATC notified us that there was an “area of severe precipitation ahead, 10 miles wide, say intentions.” That didn’t sound good, and when we tuned in to Corvallis’s weather reporting, we heard “wind 290 at 13 gusting 20, thunderstorms”. We looked at the NEXRAD display and saw that the thunderstorm was sitting just east of our destination (here, south is up and the storm is the yellow/orange blob) – right where we wanted to go to land on the runway most favored by the winds (RW 28).

We may fly into clouds, but we do not fly into thunderstorms. I’ve rescheduled a return flight before to avoid them. I’ve never had to deal with them in flight, though. After some discussion of options, I asked for a hold at DERAY, which is a waypoint on the RNAV 35 approach and looked to be far enough south to keep us well clear of the storm. The lines on the screen aren’t our track – they’re the approach, which would take us uncomfortably close to the storm. The hope was that if we circled in the hold at DERAY for a bit, the storm would move on or dissipate, clearing the way for our approach. We had plenty of fuel for this. And indeed, after 10-15 minutes in the hold, the storm had faded and I proceeded in and down towards runway 35. It wasn’t my best approach (I was too high, but better than being too low I guess! I’ll do better next time), but I successfully crabbed into the crosswind and then circled to land on 28 (winds were from 290 at 19 gusting 23, whee). That was my 75th instrument approach!

While everything worked out fine, I was a little perplexed that this thunderstorm came as a surprise. I’d gotten a weather briefing, and there were no thunderstorm warnings (otherwise I would not have flown that day). The only clues were an area of “general convective activity” over most of western Oregon, with no supporting details, and “rain showers” forecast (but rain showers do not always, or even usually, turn into thunderstorms).

After the flight, I looked up the hourly weather reports from Corvallis that had been ticking by while we were out at McMinnville. When we left at 2:30 p.m., winds were from 140 at 7 knots, clear skies. At 3 p.m. it was reporting “LTG DSNT N” (distant lightning to the north). Later reports show the thunderstorm beginning at 3:45 p.m. and ending at 4:41 p.m. We landed at 4:51 p.m.

I also considered what I would do differently if this came up again. I would have asked ATC for vectors to keep us further west of the storm on our way to DERAY. I didn’t notice any turbulence from it, but the standard advice is to stay 20 NM away, and we were closer than that. And if the storm didn’t move or dissipate, we could have diverted to Eugene, which was experiencing clear weather and is quite close.

Overall, this was another reminder that no matter when and where you fly, there’s always something new to learn. Flying is never boring, and I love the continual challenge of it!

How strong is that sunshine?

I am heading to the Cook Islands in a few weeks to explore the island of Rarotonga. This is a tiny island, covering 26 square miles and with a population of 10,000, in the south Pacific.

To prepare for the trip, I have been monitoring the weather out there. This is their rainy season, so it’s getting pounded with thunderstorms (eek!). I’m hoping it will clear up a bit before my trip.

In addition to thunderstorms, I noticed the weather report on the UV index, which has been varying from 7 to 9 during the day. At first I thought maybe the max value was 10, but then saw it go up to 11. So I looked up what exactly the UV index is. I learned that it doesn’t have a max value! It’s a measurement of the amount of “sunburn-producing UV radiation”, so it focuses on the amount of radiation in the 295-325 nm range. It is unitless, and the range is linear (so a UV index of 10 is twice as strong as 5). It was originally designed so that 10 would correspond to typical noontime summer (max) sunlight. However, this was established in 1992, and since then, higher and higher values have been observed, up to the world record of 43 (!!!) in 2003, although that value is contested and might “only” be 26.

Wikipedia’s guidelines suggest that one should limit midday exposure if the UV index is anywhere over 3, and over 6 yields “high risk of harm from unprotected sun exposure.” If it gets over 11, “unprotected skin and eyes can burn in minutes.” So, time to break out the sunscreen and protective clothing… unless I’m stuck indoors due to thunderstorms :)

Why has this winter been so warm?

This question has come up a few times recently. Even here in L.A. we’ve noticed that the winter has seemed, well, not very wintry. (During the first week in January, temperatures here were reaching the high 80’s!) Friends in states with true winter seasons have commented on the lack of snow and mild temperatures. What’s going on?

Bill Patzert, a climatologist at JPL, explains some of the mechanisms in “What Happened to All The Snow?” He cites two factors: the La Niña effect, which results in drier weather for the U.S., and something called arctic oscillation. This oscillation is a changing relationship between atmospheric pressures in the Arctic and those further south in the mid-latitudes.

Right now we are in a “strong positive” phase (corresponding to the left side of the graphic), so storms tend to be driven further north and to miss the continental U.S. So Alaskans are still getting plenty of snow!

This difference is not just anecdotal; there are quantitative measurements that we can study. Below are plots of the Arctic Oscillation (AO) Index from last winter and this winter showing how it has gone from mostly negative in 2010 to mostly positive in 2011.

Winter 2010 Winter 2011

And here is a longer-term view of the AO Index from 1950 to 2002. It’s clear why this phenomenon is referred to as an “oscillation,” although the 90’s appear to have stayed positive for quite a while.