STORM TRACK: November 30, 1981 (Volume 5 Issue 1)

John Weaver served as a forecaster and Chase Team Leader with the National Severe Storms Laboratory in Norman, Oklahoma, where he spent several years in research thru the mid-70's. Mr. Weaver is currently working at Colorado State University on satellite related forecasting research (in association with the National Earth Satellite Service).

The atmosphere is a relatively thin, gaseous envelop covering an irregular, rotating spheroid whose surface is a seemingly haphazard arrangement of variously structured elements. Heating of the atmosphere occurs quite unevenly, since (1) the inclination of the earth in its orbit exposes different latitudes to unequal amounts of solar radiation, and (2) the air absorbs little solar radiation directly, but depends upon absorption and re-radiation of the sun's rays by the varied earth's surface. For these reasons, imbalances in heating occur, and the consequence of these imbalances is motion. As great quantities of cooler, heavier air slip beneath volumes of warmer, less dense air, vast turbulent currents are born. Gravity draws the cooler masses to lower levels. Varying landscapes exert different amounts of friction on the air, and orographic features split and re-split the turbulent streams. The rapidly spinning earth 'forces' its own deviation onto the flow.

Finally, immense cloud systems are formed in rising moist air, which furnish an acceleration of their own to the newly born eddies. Like a child's kaleidoscope, weather patterns appear and disappear in an infinite number of variations -and one who looks at the sky and wonders 'what next?' is clearly approaching a problem of the most complex kind.

Over the centuries, man has dealt with the problem of forecasting weather through neces- sity. As man's population has increased, covering the globe with dwellings and industrial structures, the potential for weather elements to adversely affect him has multiplied. Large population centers represent a potential for natural devastation undreamed of a century ago. Yet, the science of forecasting has been slow to mature --not from lack of effort, but rather due to the intricate nature of the problem.

The following paragraphs outline what progress has been made, with special regard to thunderstorm prediction. The synopsis has been prepared in an historical context, so that one might better understand the sequence of thought which has brought us to the present point.

Weather prediction, prior to the advent of meteorological instruments, depended largely upon climatology and weather lore. If a region had had long winters in the past, chances were that future winters would be long -- if summers had been hot, hot summers were expected in the future, and so on. This was basic climatology and probably served man from the earliest times. But as civilizations developed, the need arose for more specific information. Sailors, merchants or travelers required advance warning of inclement weather to safeguard their journeys, their cargoes, and often their very lives. Thus, a vast catalog of weather lore was created.

Weather lore served well for many centuries. Had it not, it would have been quickly discarded. One of the earliest written listings was assembled by Aratus in about, 278 B.C.; one of the most recent, official publications was the United States Signal Service's book 'Weather Proverbs,' written in 1883 for use by its observers. And, the modern meteorologist can, with a casual look and a little thought, find much substance in these listings. Let's check a few excerpts from "Weather Proverbs.'

Mackerel sky and mares tails, make lofty ships carry low sails.

(A mackerel sky means large regions of cirrocumulus. Mares tails are long, thin streaks of cirrus. Could this proverb be talking about the approach of an extra-tropical cyclone?)

Clear moon, Frost soon.

(Low humidity, no clouds. Most, of us are aware that this implies rapid diurnal cooling --and frost in winter.)

Rain before seven, fair before eleven.

(Sounds like this one originated in a region where most precipitation came with passing shortwave troughs --itcertainly wouldn't apply on an upslope day in the High Plains.)

When the wind is in the east, 'Tis neither good for Man nor beast.

(This rule could apply equally on the eastern slopes of the Rocky Mountains, or in advance of an encrouching cyclone.)

A listing of all weather sayings would fill several volumes, and no attempt, at completeness shall be made here. The reader might enjoy obtaining a book on weather lore from the local library and trying to puzzle out the 'meteorology' behind the saying. For now, we shall simply say that many of these weather 'rules,' however limited, were often based on years of actual observation and were very often useful.

Though frequently successful in a general sense, these early methods of weather prediction fell short of ideal when used on a day to day basis, and away from the region where they had been designed. The primary weakness of these techniques was that they were simply enumerated behavioral patterns of the atmosphere (under specific circumstances), but often completely ignored the cause of these events. Success in the physical sciences comes only when accurate observations are used to deduce cause and effect relationships. Once the motivating force for an event is understood, then prediction becomes possible. But before we understand an event, we must first describe it -- and to describe it accurately, we require consistent measurements.