FORESTRY

The United States of America and their distant commonwealths, territories and islands enjoy a treasure of close to a billion acres of forest, that produces billions of dollars in annual revenues and an additional wealth of esthetic value.

Commercial and governmental interests alike have long recognized that roughshod exploitation of this priceless resource is wrong. Instead, both commercial and governmental interests have adopted policies of human stewardship that produce forests which are healthier than nature alone could provide.

Various commercial and official organizations across the country have assumed the responsibility of managing and protecting the forests. There are many factors affecting the health and productivity of the forests, most of which are under control in modern silviculture operations.

One factor that is not under control is the weather, but managers can enhance success by making appropriate decisions based on accurate weather forecasts that are tailored and formatted to precise needs.

On any particular day, the current degree of fire danger has already been determined by the state of the weather during the preceding several days to several weeks. It is from this starting point that managers must make critical decisions, among which are those regarding prescribed burning, fire mitigation procedures, advanced states of readiness and public notification. Consistently correct decisions are simply impossible without the ready availability of mission-formatted weather forecasts. For example, if the current fire danger is low and the forecast is for light winds, high humidity and partly cloudy skies, then the controlling steward can go about its normal day-to-day business, perhaps to include prescribed burning.

If the fire danger is high and the forecast is for low humidity, bright sunshine and winds in excess of 15 knots, the steward may decide to accomplish enhanced abatement and mitigation measures, including public warnings and restrictions, advanced posture, and perhaps the marshaling of augmentation personnel and equipment to especially critical zones.

There is a wide range of responses in between, the cost and value of each having to be measured against alternate responses, and all must be based to a large extent on the weather forecast. In addition, silviculture sometimes requires controlled burning of slashings or parcels of standing forest. This can be accomplished only when weather conditions favor a complete burn that will not get out of control, but another consideration is smoke and its threat to public health and safety. Therefore, the steward must also track the atmosphere's ability to disperse smoke, and the specialized forecasts must include indicators of this ability, such as the stagnation index, stability category and ventilation rate (mixing height times the average mixing-layer wind).

Let's go to the Heartland for a detailed example of what the Skywatch Weather Center did for Missouri during the 1997 fire season. Forecasting the weather for the Missouri Department of Conservation is a task that requires a comprehensive effort.

Approximately 28% of Missouri's 68,898 square miles of land area is forested. The state's climate is classified continental and is susceptible to a tremendous variety of conditions. Temperature extremes have ranged from about 20 degrees below zero (F) to around 110 degrees above, as the region can be in the path of either Gulf or Arctic air. When warm, moist gulf air is topped by very dry westerlies from the Rockies, and a trigger mechanism exists, very severe thunderstorms develop, many of which produce tornadoes. Add an occasional snowstorm, elevations that range from just over 300 feet to just under 1,800 feet, and the usual cycles of droughts and floods that the Plains are famous for, and it's obvious that forecasting weather all across the 'Show Me' state can be quite challenging. Also, since weather conditions can change very rapidly across the Plains and can vary substantially just across the state of Missouri itself, only experienced professional forecasters can consistently provide the quality of service necessary.

Fire Weather Forecasts were typically updated twice daily, and in a format that presented the Department with an easily and quickly understandable picture of what weather to expect. The normal 48-hour period covered by the forecast provided the Department with detailed planning criteria that extended through two days, while a general synoptic discussion provided a "heads up" for the third day.

The state was divided into eight fire zones. Each zone had a subset of several NWS zones. Under really unusual circumstances, we had the capability to give separate forecasts for all 23 NWS zones or any combination thereof.

The following parameters were tabulated for all eight zones every three hours for the first 24 hours of the forecast and every six hours for the next 24 hours: temperature, relative humidity, wind direction in degrees, wind speed average and gusts (mph), weather and cloud codes, precipitation probability and amount, and burning indices as calculated with the NFDRS Fuel Models A and E.

The basic forecasts were augmented with a prescribed-burn forecast that addressed the following atmospheric dispersion parameters:

morning and afternoon mixing heights

boundary layer stability class

yes/no inversion indicator

ventilation rate for 'today' and 'tomorrow'

There was also a brief, plain English narrative prescribed-burn outlook that discussed the dispersion parameters and also addressed such important issues as fog, frontal passages, unusual winds and humidity, thunderstorms and significant wind shifts not associated with frontal passage.

Finally, authorized Department members could call, toll free, for special updates. Such consultations with the forecaster can be the final factor in the decision to proceed with a prescribed burn, and can be critical during actual fire-fighting episodes when the timing and magnitude of a wind shift, for example, absolutely must be known.

 

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