Wx Watch: Winter Roundup

As I first sat down to write this, it was February 7, 2002, and I was in my home office in New Market, Maryland — in the central part of the state. It was 75 degrees Fahrenheit/25 degrees Celsius, according to the Maximum Inc. "Mini-Max" thermometer in my home weather station. I think we set a record high temperature for the date. The Mini-Max also told me that the previous night's low was 38 degrees F/3 degrees C. Meanwhile, blizzard conditions had just whacked the northern Rockies, and the Pacific Northwest was, per custom, the Home of IFR.

The weather's been like this all winter — tolerable east of the Mississippi, but with more precipitation and lousier flying conditions in the western and northwestern states. Here in the mid-Atlantic, I've counted 18 significant lows or frontal passages since last November. By significant, I mean an event causing IFR or MVFR conditions, or measurable amounts of precipitation.

West of the Mississippi, the number was up over 30. Some of these systems involved landfalls of Pacific fronts the California, Oregon, and Washington coasts, and are very typical of winter weather along the left coast.

Others were coastal systems with enough energy to make it up and over the Rockies, intensifying as they went. Still other western lows and fronts were homegrown.

Why did the eastern half of the nation have quieter weather? The main reason was the orientation of the winds aloft, beginning at the jet stream altitudes in the 30,000-foot levels and working on down. In the West, this past winter was dominated by a huge trough aloft — a southward bulge of low pressure that extended from a parent low to the north, sometimes as far north as Quebec. Look on a 500-millibar constant pressure chart from last winter and you'll most likely see one of these troughs.

It's the straight portions of the trough — the areas to the west and east of the trough's most southerly bulge — that cause all the trouble. It's these straight portions that contain the strongest winds aloft, and it's these strong winds that create lifting forces at the surface — forces that create and intensify low-pressure centers and cause crummy flying weather.

Meanwhile, the jet stream has been kinder to those of us who fly east of the Mississippi. Why? The jet stream's winds stayed mostly to the north. Because the jet stream also serves
as a boundary between colder air masses to the north and warmer air masses to the south, the mid-Atlantic and southern states enjoyed warmer-than-average temperatures, less IFR, and less precipitation.

Two fronts

From my mid-Atlantic perspective, however, I can tell you that there were days when last winter's East Coast weather did get exciting. Here's a quick rundown of two IFR weathermakers that cruised the Northeast corridor.

• January 24. On January 22, a surface low formed over southern Texas and made its way to the Northeast, edging along the Atlantic Coast. By the 24th it had teamed up with a weaker low from the Ohio Valley and slowed to a crawl. Ahead of the low's warm front, freezing rain fell in North Carolina. Forecasters had fits deciding whether rain, snow, freezing rain, or a mixture of all three would fall in the New York-to-Washington, D.C., area.

The agony hinged on the atmospheric temperature profile. As the computer models updated, the red rain/snow line snaked this way and that. To the south and east of the line, the front's precipitation would fall as rain. On the line, freezing rain was the threat. To the line's north and west, snow was expected. In the end, central Maryland got wet snow and below-instrument-approach-minimums weather, while Baltimore, Washington, and the eastern counties of the state had a cold rain and conditions that generally hovered above instrument approach minimums. Intermittently, ice pellets (also known as sleet) mixed in with rain over Washington.

This event emphasizes two things: First, 32 degrees F/zero degrees C, is a dangerous temperature — a swing of a degree or two can mean the difference between snow and the worst clear ice and biggest supercooled droplet sizes; and second, because of freezing rain's association with such a narrow temperature range, forecasters have a very difficult time pinpointing when and where it will occur. This time, forecasters made fairly accurate predictions, in spite of the chaos of temperature, moisture, and pressure variables.

• February 4. A fast-moving cold front blew through the Northeast, bringing another bout with low instrument weather to the mid-Atlantic. This event was drier than the sloppy coastal mess of January 24 — because of its origin. This system was an Alberta clipper that picked up moisture as it raced across the Great Lakes and the Appalachians. The weather was distinguished by high winds and snow squalls. In the squalls, visibilities dropped to less than one-half mile at some airports in the region. According to my Maximum "Maestro 2-S," winds gusted to 52 mph, which explains why the snow fell sideways.

An SKC flight

February 8, 2002, dawned crystal clear, just as forecast. Executive Editor Elizabeth Tennyson and I were to fly to Teterboro, New Jersey, where we'd catch a ride into New York City and attend a press conference. No airmets were posted for our flight, and forecasts all over the Northeast were for continued "SKC" — sky clear. A cold front had blasted through the day before, but now the surface winds had calmed considerably.

Aloft, it was a different story. We went to Teterboro Airport at 5,000 feet and enjoyed a turbulence-free ride with a 10-knot tailwind component. It was the return trip that was the eyeopener. Winds aloft at our 6,000-foot cruising altitude had intensified to 60 knots — all of it headwind component for the first half of the flight.

There was light-to-moderate turbulence during both the climb and the descent. The turbulence marked the shear zone between the rip-roaring winds aloft and the doldrums below.

Two more lessons: First, high-speed winds aloft don't always reside at the jet stream level; and second, calm surface winds are no guarantee of single-digit winds aloft.

E-mail the author at [email protected].

Go to

It seems like I've typed that URL several hundred times over the past few weeks. That's because so many "WxWatch" readers — my kind of people! — trusted the advice in the January edition (" WxWatch: ADDS on the Move," January Pilot).

The article dealt with a Web site having some advanced aviation weather features, grouped under the Aviation Digital Data Service (ADDS) banner. The ADDS folks were ecstatic about the article. Until they read the ADDS URL. Seems the ADDS people changed their Web address after the January issue went to press! So yours truly — and you, fellow weather afficionados — had been cruelly misled. So let me reiterate (this comes easy, I'm in practice): Go to http://adds.aviationweather.noaa.gov.

I learned of the mistake via a telephone call. "There's been a change. I just wanted to let you know before the article went out," said an ADDS staffer. "Too late. The issues are in the mail," I replied.

"Oh sugar," came the reply. Actually, he didn't use the word sugar. But he was upset. "How many people will see the article?" he wanted to know. "Oh, I'd like to think that all 380,000-plus of our members would read it," I told him. More sugaring.

This wasn't the first time pilots were upset over lack of access to ADDS. Last year the site was abruptly yanked off the Internet for a few hours. The temporary victim, it's been said, of jealous private weather vendors who objected to ADDS' free features.

Now that it's back and you know how to find it, I hope you will find the site useful. I enjoyed responding to you one-on-one, even if I did get writer's cramp from typing the URL over and over. It's gratifying to know that so many of you share an interest in the weather and take the time to read "WxWatch." — TAH