Wednesday, June 22, 2011

Weather in Motion

Last Friday's trip from KBDR down to KVKX was made interesting by weather in motion at each end of the flight. At the start, N631S and I had to wait for a line of convective activity to move out of the way and at the end we had a bit of a race to land at Potomac Airfield before some weather arrived.

The map at left (from the NWS' Hydrometeorolgical Prediction Center) shows the forecast conditions expected for 1800Z Friday. It depicts a remnant of an occluded/cold front from Lake Ontario down through lower New York with an associated region of rain and thundershowers.
And, in the event, the NEXRAD picture at 1835Z looked just about like you'd expect given that frontal picture. A line of convective weather was running from north of Poughkeepsie south through northern New Jersey. It wasn't the kind of weather you felt like going through and going around would require an extensive diversion. Better to wait it out. Unfortunately the line's speed of advance was only about 20 knots. It would be a while before it would pass to the east of Bridgeport so that N631S and I could head west.

At 2130Z (5:30PM local time) it was raining pretty hard at KBDR and by 2200Z it had slacked off to a drizzle as I did my pre-flight on N631S. There was still active weather lurking not far to the southwest but the radar picture looked good to the northwest. Runway 24 was active so when I picked up my clearance I asked the tower controller to request, on my behalf, an early turn to the northwest. I was pleased, after I taxied to the runway, to hear, "Skylane 631 Sierra, cleared for takeoff; on departure turn right to heading 330."

This screenshot of the Garmin 396, about ten minutes after departure, shows active cells to the south and clear weather ahead. Looking at it you'd think that I was in an area of moderate precipitation but in fact, here's what I saw out the window at 6,000 feet:

Once clear of the departure weather, the flight west across lower New York and into Pennsylvania was uneventful. At 8,000 feet for most of the trip, all of the clouds were below, the air was smooth and the winds were even a bit favorable. It wasn't until the Lancaster area that weather in motion once again became a subject of interest.

The storm cell (left) between Westminster (EMI) and Martinsburg (MRB) is the potential villain. It was moving fairly quickly southeast, straight for KVKX. Gaging the distances and speeds involved I thought I'd have time to land before the weather arrived.

But it was going to be a bit close. For the next 75 miles I watched that weather as I flew through Potomac Approach's airspace. If the weather got to KVKX before I did, then Plan B was to ask Approach to vector me off to the south somewhere and let me hold until the storm moved on. I hoped it wouldn't come to that.

Fortunately, N631S won the race. Wheels on the runway at 0035Z, and the rain began five minutes later. I got a bit wet putting the airplane into its hangar but by the time everything was secured it had stopped.

Weather is always in motion. Sometimes (as with my departure weather) you wish it would move faster. Sometimes (as on arrival) you wish it would move slower. But always, you have to think about and adapt to the trend and the timing.

For the record, courtesy of the good folks at FlightAware.com, here's the track for the flight.

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