Tuesday, July 24, 2012

Fortunate Timing

When N631S and I departed KVKX for our northbound trip to Connecticut on Monday the forecast for KBDR, the destination airport, was quite reasonable. It called for a light southwesterly breeze, good visibility and scattered high clouds. There was the possibility of periods of light rain but these were expected to be over by 8:00 AM.

KBDR 230949Z 2310/2406 23006KT P6SM SCT120 BKN250
       TEMPO 2310/2312 6SM -SHRA BKN035 
       FM231500 22009KT P6SM SCT050 BKN140
       TEMPO 2318/2322 6SM TSRA SCT025 BKN040CB 
       FM232200 22010KT P6SM VCSH BKN050 BKN120 
       FM240000 23005KT P6SM SCT050 BKN150= 
But things were a bit more complicated than that. There was also a Convective SIGMET in effect for thunderstorms with tops above 40,000 feet. They were at that time between Albany and Poughkeepsie, headed southeast. Toward Bridgeport.

I decided that since the weather on my intended route was good and the only question involved what the situation on arrival would be, it made sense to get underway and to work out options and alternates en route.

N631S was off the ground at 11Z. As soon as we were level at 7,000 feet, our final cruising altitude, I had a look at what the NEXRAD display would tell me. As you see at left, the first lot of stormy weather was passing KBDR. It was moving southeast at about 20 knots.
I panned the NEXRAD display on the GPS396 to the north and west and saw a second, larger area of weather coming along behind the first. It appeared that these storms would be influencing the area I was headed toward for some time to come. Without a doubt, it was time for some planning.

I took note that there was a clear area about ten miles wide between the areas of weather. With fortunate timing, the gap might accommodate my flight path from JFK to Bridgeport. I'd press on, and see if my luck was good.

Plan 'B' would be to land early and wait out the weather. There were a couple of places available for that. Miller Air Park in Toms River, NJ (KMJX) would work as would Belmar (KBLM). I'd watch the evolving weather picture and pick a spot to land if that seemed advisable.

Plan 'C' would be in effect if the situation kept looking good long enough to get me into the New York Class 'B' airspace and then quickly became unacceptable. Then I'd need to get New York Approach to help with weather avoidance vectors to an airport of refuge on Long Island or back in New Jersey.

With that thought process completed, I pressed on. With about 40 minutes to go, the first batch of weather had moved on and dissipated. It was no longer a factor. The second batch was moving toward the coast. The leading edge of the precipitation was about 20 miles from KBDR and the heavier returns were about 10 miles further out. I had already passed KMJX and decided to press on past KBLM. At this point I felt I had a good chance of reaching KBDR ahead of any significant weather.
Crossing JFK, and with 18 minutes to go, there was still about 10 miles between KBDR and even light rain. This was looking quite good. I felt that I had enough margin, even considering the well known NEXRAD latency issues and in case of need I could stay to the south and divert to either New Haven (KHVN) or Groton (KGON).

Conditions on the ground at KBDR were still good. New York Approach cleared me direct to KBDR and with less than 10 minutes left in the trip, I relaxed. I flew past the field, turned back to land on Runway 24 and taxied to parking. As I was putting the cover on N631S, light rain began.

Sunday, July 22, 2012

Sufficiently Interesting

My friend Craig from Oregon sort of wondered, in a recent comment, where N631S and I have been. He said: "FlightAware says N631S has been flying. Any details to share?"

I responded to the effect that "the flying has been pretty uneventful (i.e., not great blogfodder)" and in fact it's been six or seven weeks of pretty routine back and forth between Potomac Airfield (KVKX) and Bridgeport's Sikorsky Memorial (KBDR). However, this past Friday's southbound trip was interesting enough to talk about.

It was clear from the beginning that, at the least, we were going to get wet. The early chart from NCEP valid for 18Z showed a double-barreled surface low over southern Pennsylvania and Maryland with a stationary front trailing off to the east-southeast and widespread showers.

The Terminal Area Forecasts issued at 12Z looked pretty reasonable:

KBDR 201120Z 2012/2112 09013KT 6SM -SHRA SCT020 OVC050 
     FM201500 08014KT 4SM -RA BR OVC020 
     FM202300 07012KT 5SM -DZ SCT020 OVC025 
     FM210400 05010KT P6SM OVC035
KDCA 201125Z 2012/2112 33006KT P6SM BKN015 OVC060 
     FM201600 VRB05KT P6SM VCSH FEW030 BKN040 
     FM202000 31008KT P6SM VCTS BKN040CB 
     FM210300 03006KT 4SM BR VCSH SCT015 BKN030 
     FM210500 01013KT 4SM BR SCT009 BKN015
The forecast for a late-afternoon departure from KBDR was fine – four miles visibility in light rain and mist, moderate northeast wind and a 2,000 foot overcast. Nothing to be concerned about.

The arrival forecast for the Washington area (using KDCA) had something that would bear watching. From 4:00 PM local time, it anticipated thunder-showers in the vicinity and a broken ceiling of cumulonimbus clouds at 4,000 feet. Supporting that, the mid-morning Collaborative Convective Forecast (CCFP) map valid for 21Z showed widespread sparse convective activity, predicted with low confidence (the gray stuff) but with areas of higher confidence (the blue stuff) located where it might prove interesting to me.

I talked about that "VCTS" tag in the TAF back in May. It seems to follow from a forecast for scattered or sparse convective activity and is flyable with good on-board weather depiction and basic visual conditions. I'd have both, so the VCTS wasn't a "no go" item, but it did demand respect.

So, I was good to go but I continued to keep a watchful eye on the evolving forecast. And I was pleased to see the 18Z TAF's. Neither the forecast nor the view out of my office window had changed much regarding my departure, but things were looking up for arrival.

KDCA 201733Z 2018/2118 32007KT 6SM -RA BKN010 BKN035 OVC100 
     FM202000 36010KT P6SM BKN025 OVC150 
     FM210200 02012KT 5SM -SHRA VCTS BKN015 OVC040CB 
     FM210600 01008KT 4SM BR BKN007 
     FM211600 02007KT P6SM SCT007 BKN015
Basically, the forecast thunder-showers had been pushed out to later in the evening, well after my ETA. That was a nice piece of news. So, shortly thereafter, off to the airport!

N631S and I took off in light rain, but it was clear that the weather was breaking up quickly. After departing Runway 6 at KBDR and turning to the north, I was able to snap the picture at left showing what amounts to visual conditions over the Housatonic River. There were clouds and bursts of precipitation during the initial climb to 6,000 feet but it was the ragged edge of the weather. Just a few seconds later I captured the NEXRAD screen below.

This image makes it clear that there would not be much precipitation to deal with, at least for the first half of the trip. Of course, NEXRAD doesn't show clouds. Upon reaching the Hudson River, ATC asked for a climb to 8,000 feet. That put N631S into the clouds and there we stayed for most of the flight.

Having gotten the departure under control, it was time to look at how the weather was developing at the destination. I panned the NEXRAD display down to the south and got this:

Here too, the precipitation seemed to be departing to the east, and there was no sign of the convective activity that had been in the earlier forecast. Things were definitely looking good. The next step was to check recent METAR's for airports near KVKX to get an idea of current conditions. Early in the flight, here's what Washington National, Andrews, and Davison Army Airfield were reporting:
METAR KDCA 201952Z 35005KT 10SM -RA BKN017 BKN023 OVC040
           27/22 A2992 RMK AO2 SLP130 P0000 T02720217=

METAR KADW 201955Z AUTO 06007KT 7SM -RA BKN007 OVC015 24/23
           A2992 RMK AO2 RAB1941DZE1941 CIG 006V008 SLP131
           P0001 T02410232 $=

METAR KDAA 201955Z AUTO 29004KT 10SM -RA CLR 27/21 A2992
           RMK AO2 RAB1950 SLP132 P0000 T02690214=
The most interesting part of that was, of course, the marginal weather at Andrews AFB. Only about four miles from KVKX, Andrews is a better predictor of conditions at my home field than Washington National. Andrews had good visibility in light rain, but a broken ceiling at 700 feet. That's pretty low! It was time to break out the approach plate for the RNAV Rwy 6 instrument procedure at KVKX and hope that conditions would be improved on arrival.

The Minimum Descent Altitude (MDA) for the approach to Runway 6 at KVKX is 680 feet MSL – 562 feet above the touch-down zone elevation (TDZE). A 700 foot ceiling cuts things fairly thin. One piece of good news was that the METAR's indicated winds favoring Runway 6. I would not need to worry about circling to Runway 24. The MDA for a circling approach is 60 feet higher, which would cut the margin further.

Just to make things a bit more entertaining, I hadn't flown the RNAV approach into KVKX since March. I'm current, but all my recent approaches have been at Bridgeport.

The flight continued smoothly and uneventfully past Allentown and Lancaster, and down to Baltimore. Passing Baltimore I rechecked the conditions at Andrews. Not much had changed:

METAR KADW 202155Z AUTO 04006KT 10SM OVC007 23/22 A2992 RMK
           AO2 RAB2102E212136DZE2102B2136E2138 SLP131 P0004
The rain had ended and visibility was a bit improved. The ceiling, still at 700 feet AGL, was now a solid overcast rather than broken. The recorded ATIS at Potomac Airfield (KVKX) was reporting winds five knots at 080. It doesn't report ceiling.

ATC asked my intentions and I said I'd like the RNAV 6 approach. "You can expect that," was the reply. I planned to shoot the approach, and if I had to miss, I'd go around and try one more time. A second miss and I'd divert to Manassas. I have a rule about never shooting an approach a third time.

Potomac Approach vectored N631S and me to the southwest and brought us down to 2,000 feet. Then we were cleared direct to WOBUB, the Initial Approach Fix (IAF), to begin the instrument approach. This picture, approaching WOBUB, looks off to the northeast toward KVKX, about 10 miles away.

The approach was routine and we broke out of the clouds at 800 feet, two to three miles from the threshold. It was nice to land and put N631S away, but if the cloud bases had been 200 feet lower the tale would have gotten longer and more interesting. I thought it was sufficiently interesting as it was.