The Weather Never Sleeps

On second glance, maybe the weather isn't so good

Let's join my good friend and stalwart pilot, Dudley Flyright, as he plans a VFR flight across Minnesota to the mythical home of Lake Woebegon. Departing from Fargo, on the eastern edge of North Dakota, we'll fly to Duluth, on the eastern edge of Minnesota, and use actual weather data from a September Sunday. This is a 210-nautical mile, two-hour pleasure flight. We'll shoot for a leisurely 10 a.m. takeoff, and navigate via the Park Rapids (PKD) and Grand Rapids (GPZ) VOR/DMEs.

Dudley takes a bird's eye view of the weather the day before the flight. Looking at Sunday's forecast map in Saturday's USAToday, the flight seems to be a no-brainer. A big area of high pressure, your basic continental polar air mass, is moving from Canada into the upper Midwest. Fortunately, Dudley knows one simple picture can't tell the whole weather story, so he downloads the Fargo and Duluth TAFs from DUATS just before noon on Saturday.

First he subtracts five hours from the reports' universal coordinated time (UTC, or Zulu) to get central daylight time. Between 4 and 10 a.m. Sunday, the Fargo TAF predicts a 30 percent chance of five statute miles visibility in thunderstorms and light rain, and a ceiling of broken cumulonimbus (CB) clouds at 5,000 feet [PROB30 0915 5SM -TSRA BKN050CB]. After 10 a.m. the TAF predicts an eight-knot wind from 160 degrees, more than six-miles visibility, and a ceiling of broken clouds at 12,000 feet [FM1500 16008KT P6SM BKN120].

The Duluth TAF doesn't offer much because Sunday morning is at the end of its effective period. From 9 a.m. (1400 Zulu), it predicts a seven-knot wind from 120 degrees, more than six miles visibility, and ceiling of broken clouds at 1,000 feet, with the clouds becoming scattered at 2,000 feet between 10 and 11 a.m. [FM1400 12007KT P6SM BKN010 BECMG 1516 SCT020].

The weather isn't as cheery as the map suggests, and our VFR flight is in question. Dudley knows TAFs are good for a 24-hour period, and that they are issued every six hours. Hoping for better weather, Dudley downloads the new TAFs Saturday evening. Forecasters predict the same weather for Fargo between 3 and 7 a.m., except they now expect the ceiling of broken CBs to be at 2,500 feet [PROB30 0812 -TSRA BKN025CB]. After 10 a.m. Sunday, the TAF predicted the same weather as before.

Duluth's new TAF predicts worse rather than improving weather. Starting at 9 a.m., it predicts a seven-knot wind from 140 degrees, five miles visibility in mist, and a ceiling of broken clouds at 1,000 feet. Between 10 a.m. and noon - our approximate arrival time - the weather should become six miles visibility, no significant weather, such as rain, and scattered clouds at 2,000 feet [FM1400 14007KT 5SM BR BKN010 BECMG 1517 P6SM NSW SCT020].

The predicted visibility is within Dudley's personal VFR minimums, but the ceilings don't quite make the grade. He also reminds us that forecasts, as far as accuracy goes, are just a dress rehearsal. Rising early Sunday morning, Dudley downloads the latest satellite picture. It shows clear skies across much of the country except for New England and- wouldn't you know it- the north central states.

Next, he downloads the current weather depiction chart, which gives a good broad view of ceilings and visibility (showing where it is VFR, MVFR or IFR). The simplified station models show visibility (if it's six statute miles or less), sky cover, cloud bases, weather (obstructions to vision such as rain or mist), and fronts from the surface analysis chart (its big brother) for the preceding hour. Dudley prefers this visual representation to its textual equivalent of "SYNOPSIS...CDFNT CLE-BDF BECMG STNRY BDF-OMA-RAP. WMFNT RAP-50W ISN. TROF OVR LH-ERN LS."

As Dudley examines the chart, he sees it doesn't depict the weather between the reporting stations, just the meteorologist's interpolation of the en route weather based on the reporting stations. The chart is updated every three hours, so that means there's a delay between the chart's data and the transmission of it. Dudley is examining data that are already several hours old, and the Sunday morning chart depicts IFR conditions along much of our route. So much for our no brainer.

To support his no-go decision - and get the most current information - Dudley calls DUATS for a full data dump - a standard briefing. The area synopsis gives us general area descriptions of clouds and weather and calls for 3,000 to 5,000-foot ceilings, widely scattered rain showers, and scattered light thunderstorms by mid-afternoon in both northern and southern Minnesota.

Then there's AIRMET Sierra for IFR conditions, and the most recent METARs support it. Park Rapid's ASOS reported a six-knot wind from 120 degrees, 1.5 miles visibility in mist, a ceiling of broken clouds at 100 feet and an overcast layer at 2,300, and a temperature/dewpoint spread of one degree [AUTO 12006KT 1 1/2SM BR BKN001 OVC023 13/12]. There's not much pleasure in that report.

The TAFs sing the same song of poor weather, and the winds aloft at Grand Forks and Duluth both show lower level winds out of the south at about 10 knots and out of the west also at about 10 knots, at 6,000 and 9,000 feet. Dudley concludes that the IFR weather might not be clearing out any too quickly. It's the final check in the no-go column, and Dudley is wishing he'd finished training for his instrument rating.

Dudley promised to fly another day when the weather was better. As we left, Dudley was on the telephone - with an instrument flight instructor, I think - discussing some unfinished training.