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
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
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
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
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
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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