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Old 05-17-2002
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Michael Carr is on a distinguished road
Tornadoes and the VOR


When the restart day came for Leg Seven of the Volvo Ocean Race, so did extreme weather, with tornadoes reported not far away. Team SEB gets underway in strong winds and driving rain.
Several weeks ago, I had big plans to go out on the Chesapeake Bay and watch the re-start of the Volvo Ocean Race. I was hoping for a sunny day and winds in the 15-knot range, but this wish was not granted. On Saturday, the day before the re-start, a ridge of high pressure hung over the East Coast and the day was sunny and cloud-free with cool, dry winds coming in from the north. If only this ridge would have stayed in place for another 24 hours.

That wasn’t the case though, because the ridge was quickly being dragged east and out to sea by upper level winds of 70-plus knots. By Saturday afternoon cirrus clouds had veiled the upper sky and by evening low-level clouds were moving in to obscure anything above them. The surface winds had also shifted from the north and began strengthening out of the south.

By Saturday night rain began to fall as a gale-force system moved over the east coast replacing the ridge that was by then far out into the Atlantic. At this point I began to realize that my desired ideal conditions for viewing the start of the VOR were not going to materialize. It wasn’t just the rain; this low-pressure system had timed its arrival over the Chesapeake Bay in such a way that it meant the possibility of extreme weather.

Several key ingredients set up the extreme weather the spectators and the VOR crews experienced the following day. First, this low moved over the Chesapeake Bay during the afternoon, the hottest time of day, when convective (upward) motion in the lower levels of the atmosphere are the strongest. Next, this low was being supported by a very vigorous upper level flow, rapidly exhausting rising air within the low, thus allowing surface air to quickly flow inward at the surface. And finally, cold, dry air flowing down the eastern side of the Appalachian Mountains was displacing the warm surface air over the Bay.


Tornadoes aren't a phenomenon that sailors often have to worry about, but when they occur onshore, chances are the weather is unstable and near extreme on the water nearby.
Timing, as they say, is everything, and certainly with weather it is a major factor. This low-pressure system had timed its arrival over the Chesapeake Bay at a time when its continued development would be well supported. By early Sunday morning, I had made the decision not to go out in my 13-foot Boston Whaler to view the race. My initial plan had been to make it a family outing; my six-year-old daughter is the qualified coxswain for the boat! But now I wasn’t feeling warm and fuzzy about the impending afternoon conditions.

Even though I would not have predicted how extreme the weather became, in retrospect it doesn’t seem surprising. That Sunday afternoon, severe tornadoes formed over the land between the Potomac River and the Chesapeake Bay—tornadoes so severe that subsequent damage indicated winds had exceeded 200 mph! Though the Chesapeake Bay and the Volvo fleet and its numerous spectator craft were not directly affected, it sure made me value being on land and not on the water in a little runabout. From the safety of home, my mind conjured visions of Dorothy and Toto in the Wizard of Oz flying through the air, except that it was my family and me floating through the air in a Boston Whaler.

So we did not get out to witness the re-start of the VOR. Instead I made sure the boat plug was out of the Whaler as it sat on its trailer so it would not fill with the buckets of rain that continued to fall the entire afternoon.


On the day of the VOR restart, this NOAA chart indicated gale-force winds at sea. Where he's added the word "tornado" in the middle of the chart is just at the northern end of the Chesapeake Bay.
So what can we learn from this weather sequence? The main lesson is that low-pressure systems that show development to gale or storm force status should be critically watched. If they pass over your area in the afternoon, severe weather is highly likely. An area where squalls and the strongest thunderstorms are likely to occur is on the south side of lows between the warm and cold fronts. Especially in the region preceding the cold front where cold air displaces warm air. This displacement brings about strong upward, convective motion and this dynamic brings strong gusty surface winds supporting the possible formation of tornadoes, thunderstorms, and microbursts.

If you find yourself in such a region and have access to the Internet, it is well worth viewing Doppler radar images. These can be accessed real time via the regional National Weather Service Internet website. Obviously when you’re underway aboard your boat, this option isn’t so feasible, but there are many times when you might find yourself moored at a marina or within cell phone coverage and can take advantage of this information.


This upper-air chart captured on the day after the VOR restart shows the dashed line representing the surface trough well out to sea off the coast of New England and the Mid Atlantic states.
I have attached a surface chart for Sunday afternoon with an annotation showing where the tornadoes occurred, as well as an upper air chart (500-mb) for Monday morning. Note both the gale notation for this low and the 70-knot winds in the upper level flow. As you look closely you will also see the dashed surface trough line to the east of the surface cold front. This surface trough line indicates unstable and dynamic surface activity. Since this low moved almost due east, its southern sector—that region between and warm and cold front—passed directly over the Chesapeake Bay on Sunday afternoon.

I’m sure that after the start of that leg, the Volvo racers were pleased to get free of the confining Chesapeake Bay and charge across the Atlantic. Thinking about this leg of the Volvo brings back memories from four years ago when I was a member of the crew on a Whitbread 60 being delivered to the UK for the start of last race. We crossed the Atlantic in 13 days, averaging 18 to 20 knots over more than 3,000 miles, and on our best day’s run we covered over 350 miles. It was a wild, wet ride!



Suggested Reading:

Route Planning 101 by Michael Carr

West to East Across the Pond by Michael Carr

Hurricane Warning by Ralph Doolin

 

SailNet Store Section: Weather Instruments

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