Fire Weather System
Georgia Forestry Commission
Georgia Forestry Commission's (GFC) fire weather system is an enhanced version of the forecast segment of the Forestry Weather Interpretation System (FWIS) developed at the Southern Forest Fire Laboratory in cooperation with the southern forestry community in the late 70’s and early 80’s (Paul 1981, Paul and Clayton 1978). When the pilot test of FWIS was completed, GFC adapted parts of the system for their use. Adaptations included an expansion of the forecast variables, and a sophisticated automation process. The automation process is especially important because the system will run automatically even if there is no staff meteorologist to monitor the operation. During normal working hours (8am-430pm Monday through Friday), staff meteorologist may intervene and make manual changes to the forecast as required. The automation process sets limits such that a “small” forecast error may occur, but a “large” error is unlikely. Whenever fire danger is high, or other critical weather driven forestry events are occurring, staff meteorologist may work after hours, weekends or holidays.
3-day 5-period forecasts are generated twice per day ( and ) for each district or district component. 7-day forecasts are generated in the morning only. Most districts are not split, but some are split into North-South, or coastal-inland components. Districts that are climatologically similar may be combined for forecast purposes, if combining is operationally acceptable. The forecast is for a geographic area, and consequently variables such as temperature, relative humidity and wind are specified as a range of values most likely to occur over the district.
addition to the text weather forecasts, maps and graphs of selected observed
or forecast weather and fire related variables are produced. Current and
forecast fire danger rating information for GFC and co-operators weather
station network are generated. Current weather at National Weather
Service's (NWS) weather stations in
NFDRS stands for National Fire Danger Rating Systems. The current version of the National Fire Danger Rating System was developed by the US Forest Service (Burgan, 1988) for predicting fire occurrence and behavior based on fuels, topography, man‑caused fire risk factors and current weather conditions. Although the National Fire Danger Rating System indices should not be directly applied to any particular site, they do supply the practitioner with a set of indices that can be used to compare recent history, and adjacent fire management areas. Thus, it is very important to understand the principles of fire danger rating:
Experienced practitioners can translate these general area based indices to probable fire behavior at specific burn site. Detailed explanation of the fire danger indices can be found by clicking "Explanation of NFDRS Indices" on the fire weather homepage.
Weather data are input into NFDRS and a number of indices are produced. These fire danger indices are used to support prescribed burning activities and wildfire control operations. Weather data are collected automatically daily at Then, fire danger indices will be computed. Weather stations can be called at any time when data are needed to support forestry operations.
Weather Station Network
GFC operates a network of
19 automated weather stations throughout the state (Figure 1). The stations record current weather
conditions each hour. Weather data
from stations maintained by cooperating agencies, including US Forest
Service, US Park Service, Department of Defense and
GFC currently uses NFDRS fuel models C, D, and E. Definitions of the various fuel models are included in (Appendix A). Location and fuel model associated with each station is shown in Table 1. The Georgia Forestry Commission uses Burning Index (BI) to determine Class Day. The determination points are station specific based on BI percentile distribution at the station. The BI determination points for all the stations are listed in Table 2.
Table 1. Name, location, elevation, and NFDRS fuel model used for the weather stations accessed by the GFC (excluding UGA stations)
The stations are owned by the GFC unless the station name is followed by an abbreviation in
parenthesis i.e. (USFS). The abbreviations are noted below.
DoD - Department of Defense
NPS - U.S Department of Interior, Park Service
All Locations are North latitude and West(-) longitude.
Table 2: Class Day determination points
Note: The listed values are the minimum value for each Class day. For example, when Watkinsville has BI of 19-22, it has Class 4 Day.
Deeming, John E.; Burgan,
Robert E.; Cohen, Jack D. The National Fire-Danger Rating System – 1978. 1988
Revisions to the 1978 National Fire-Danger Rating System. General Technical Report INT-39.
Paul, J.T., and J. Clayton. User manual: Forestry Weather Interpretation System (FWIS). Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station and Atlanta, GA: Southeastern Area State and Private Forestry, in cooperation with the U.S. National Weather Service, NOAA, Silver Spring, M;. 1978. 83pp.
FUEL MODEL DEFINITIONS
Definitions extracted from (Deeming, et al. 1977).
FUEL MODEL A
This fuel model represents western grasslands vegetated by annual grasses and forbs. Brush or trees may be present but are very sparse, occupying less than one third of the area. Examples of types where Fuel Model A should be used are cheatgrass and medusahead. Open pinyon-juniper, sagebrush-grass, and desert shrub associations may appropriately be assigned this fuel model if the woody plants meet the density criteria. The quantity and continuity of the ground fuels vary greatly with rainfall from year to year.
FUEL MODEL B
Mature, dense fields of brush 6 feet or more in height are
represented by this fuel model. One-fourth or more of the aerial fuel in such
stands is dead. Foliage burns readily. Model B fuels are potentially very
dangerous, fostering intense, fast-spreading fires. This model is for
FUEL MODEL C
Open pine stands typify Model C fuels. Perennial grasses and forbs are the primary ground fuel but there is enough needle litter and branchwood present to contribute significantly to the fuel loading. Some brush and shrubs may be present but they are of little consequence. Situations covered by Fuel Model C are open, longleaf, slash,ponderosa,Jeffrey, and sugar pine stands. Some pinyon-juniper stands may qualify.
FUEL MODEL D
This fuel model is specifically for the palmetto-gallberry understory-pine overstory association of the southeast coastal plains. It can also be used for the so-called "low pocosins" where Fuel Model 0 might be too severe. This model should only be used in the Southeast because of a high moisture of extinction.
FUEL MODEL E
Use this model after leaf fall for hardwood and mixed hardwood-conifer types where the hardwoods dominate. The fuel is primarily hardwood leaf litter. The oakhickory types are best represented by Fuel Model E, but E is an acceptable choice for northern hardwoods and mixed forests of the Southeast. In high winds, the fire danger may be underrated because rolling and blowing leaves are not accounted for. In the summer after the trees have leafed out, Fuel Model E should be replaced by Fuel Model R
FUEL MODEL F
Fuel Model F is the only one of the 1972 NFDRS Fuel Models whose
application has changed. Model F now represents mature closed chamise stands and oakbrush
FUEL MODEL G
Fuel Model G is used for dense conifer stands where there is a heavy accumulation of litter and downed woody material. Such stands are typically overmature and may also be suffering insect, disease, wind, or ice damage-natural events that create a very heavy buildup of dead material on the forest floor. The duff and litter are deep and much of the woody material is more than 3 inches in diameter. The undergrowth is variable but shrubs are usually restricted to openings. Types meant to be represented by Fuel Model G are hemlock-Sitka spruce, Coast Douglas-fir, and windthrown or bug-killed stands of lodgepole pine and spruce.
FUEL MODEL H
The short-needled conifers (white pines, spruces, larches, and firs) are represented by Fuel Model H. In contrast to Model G fuels, Fuel Model H describes a healthy stand with sparse undergrowth and a thin layer of ground fuels. Fires in H fuels are typically slow spreading and are dangerous only in scattered areas where the downed goody material is concentrated.
FUEL MODEL I
Fuel Model I was designed for clearcut conifer slash where the total loading of materials less than 6 inches in diameter exceeds 25 tons/acre. After settling and the fines (needles and twigs) fall from the branches, Fuel Model I will overrate the fire Potential. For lighter loadings of clearcut conifer slash, use Fuel Model J, and for light thinnings and partial cuts where the slash is scattered under a residual overstory, use Fuel Model K.
FUEL MODEL J
This model complements Fuel Model I. It is for clearcuts and heavily thinned conifer stands where the total loading of materials less than 6 inches in diameter is less than 25 tons/acre. Again, as the slash ages, the fire potential will be overrated
FUEL MODEL K
Slash fuels from light- thinnings and partial cuts in conifer stands are represented by Fuel Model K. Typically the slash is scattered about under an open overstory. This model applies to hardwood slash and to southern pine clearcuts where the loading of all Fuels is less than 15 tons/acre.
FUEL MODEL L
This fuel model is meant to represent western grasslands vegetated by perennial grasses. The principal species are coarser and the loadings heavier than those in Model A fuels. Otherwise the situations are very similar; shrubs and trees occupy less than one-third of the area. The quantity of fuel in these areas is more stable from year to year. In sagebrush areas Fuel Model T may be more appropriate.
FUEL MODEL N
This fuel model was constructed specifically for the sawgrass prairies of south
FUEL MODEL O
The O fuel model applies to dense, brushlike
fuels of the Southeast. O fuels, except for a deep litter layer, are almost
entirely living in contrast to B fuels. The foliage burns readily except
during the active growing season. The plants are typically over 6 feet tall
and are often found under an open stand of pine. The high pocosins
FUEL MODEL P
Closed, thrifty stands of long-needled southern pines are characteristic of P fuel: A 2- to 4-inch layer of lightly compacted needle litter is the primary fuel. Some small diameter branchwood is present but the density of the canopy precludes more than a scattering of shrubs and grass. Fuel Model P has the high moisture of extinction characteristic of the Southeast. The corresponding model for other long-needled pines is U.
FUEL MODEL Q
Upland Alaskan black spruce is represented by Fuel Model Q. The stands are dense but have frequent openings filled with usually inflammable shrub species. The forest floor is a deep layer of moss and lichens, but there is some needle litter and small-diameter branchwood. The branches are persistent on the trees, and ground fires easily reach into the tree crowns. This fuel model may be useful for jack pine stands in the Lake States. Ground fires are typically slow spreading, but a dangerous crowning potential exists. Users should be alert to such events and note those levels of Spread Component (SC) and BI when crowning occurs.
FUEL MODEL R
This fuel model represents the hardwood areas after the canopies leaf out in the spring. It is provided as the off-season substitute for E. It should be used during the summer in all hardwood and mixed conifer-hardwood stands where more than half of the overstory is deciduous.
FUEL MODEL S
Alaskan or alpine tundra on relatively well-drained sites is the S fuel. Grass and low shrubs are often present, but the principal fuel is a deep layer of lichens and moss. Fires in these fuels are not fast spreading or intense, but are difficult to extinguish.
FUEL MODEL T
The bothersome sagebrush-grass types of the
FUEL MODEL U
Closed stands of western long-needled pines are covered by this model. The ground fuels are primarily litter and small branchwood. Grass and shrubs are precluded by the dense canopy but occur in the occasional natural opening. Fuel Model U should be used for ponderosa, Jeffrey, sugar pine, and red pine stands of the Lake States. Fuel Model P is the corresponding model for southern pine plantations.