Fire Danger

XHTML 1.0 Strict Page for Fire Danger Graphics

The graphs below are calculated using recent weather data observations and offer an overview of fire weather conditions for Coastal and Inland Areas of Southeastern North Carolina and Northeastern South Carolina. A summary of terminology is shown below the table.





DateTemp
ºF
Humidity
%
Wind Speed
mph
Rainfall
in
FFMCDMCDCISIBUIFWIFWI DCFFDIFFDI DCDFBKDIFFDCFFD
kW/m²
SFDCFMIPeak Temp
ºF
Peak Humid
%
Peak Wind
mph
10/22/201781.1604.00.0088.016504.4186.5MD1.7LM50MD40EX18.481.6614.0
10/21/201780.5521.00.0088.014453.5164.9MD1.0LM50MD16EX16.481.2532.0
10/20/201777.2490.00.0087.312392.9133.6MD0.0LM50LW6EX15.977.4490.0
10/19/201770.8492.00.0085.49342.6112.8LW0.9LM50LW2EX17.378.8552.0
10/18/201770.0451.00.0079.67291.290.7LW0.7LM70LW0HI16.070.0451.0
10/17/201760.3704.00.1063.35250.770.4LW0.9LM30LW0HI20.963.5614.0
10/16/201784.0710.00.0075.57210.880.4LW0.0LM50LW0HI21.084.2730.0
10/15/201781.5710.00.0066.65160.660.3LW0.4LM50LW0HI20.381.9691.0
10/14/201771.1851.00.0052.64100.240.1LW0.4LM60LW0MD25.972.0861.0
10/13/201776.8773.01.3740.0350.030.0LW0.0LM00LW0LW23.277.5783.0
Terminology
FFMC Fine Fuel Moisture ContentDMC Duff Moisture Content
DC Drought Code ISI Initial Spread Index
BUI Build Up index FWI Fire Weather Index
FWI DC Fire Weather Index Code FFDI DC Forest Fire Danger Index Danger Code
GFDI DC Grass Fire Danger Index Danger Code DF Drought Factor
BKDI Byram-Keetch Drought Index FFDC Forest Fire Danger Code
GFDC Grassland Fire Danger Code CBI Chandler Burning Index
CBI DC Chandler Burning Index Drought Code    

Chandler Burning Index
LOW
<50
MOD
50-75
HIGH
75-90
V HIGH
90-97.5
EXTREME
97.5+

The Chandler Burning Index (CBI) uses the air temperature and relative humidity to calculate a numerical index of fire danger. That number is then equated to the Fire Danger severity of either extreme, very high, high, moderate, or low. It's based solely on weather conditions, with no adjustment for fuel moisture.


Fire Weather Index
LOW
0.0-4.9
MOD
5.0-13.9
HIGH
14.0-20.9
V HIGH
21.0-32.9
EXTREME
33.0+

To interpret the system, the three fuel moisture codes and the three behaviour indices need to be understood. Each code and index is a numerical rating related to likely fire behaviour. The scales start at zero, and except for the Fine Fuel Moisture Code which has a maximum of 99, all are open-ended. Low ratings indicate high moisture content, and ratings rise as moisture content decreases. Ratings rise as fire weather becomes more severe.


Drought Code
LOW
0.0-79.9
MOD
80.0-209.9
HIGH
210.0-273.9
V HIGH
274.0-359.9
EXTREME
360.0+

The DC is a numerical rating of the moisture content of deep, compact, organic layers. It is a useful indicator of seasonal drought and shows the likelihood of fire involving the deep duff layers and large logs. A long period of dry weather (the system uses 52 days) is needed to dry out these fuels and affect the Drought Code. A DC rating of 200 is high, and 300 or more is extreme indicating that fire will involve deep sub-surface and heavy fuels. Burning off should not be permitted when the DC rating is above 300.


Byram-Keetch Drought Index
MILD
0.0-99
AVERAGE
100-248
SERIOUS
249-315
SEVERE
316-390
EXTREME
391+800

The Byram-Keetch Drought Index (BKDI) attempts to measure the amount of precipitation necessary to return the soil to full field capacity. It is a closed system ranging from 0 to 203 units (0 - 800 imperial) and represents a moisture regime from 0 to 203 millimetres (0 - 8 inches) of water through the soil layer. At 203 millimetres (8in) of water, the KBDI assumes saturation. Zero is the point of no moisture deficiency and 203 (800) is the maximum drought that is possible. At any point along the scale, the index number indicates the amount of net rainfall that is required to reduce the index to zero, or saturation.

The inputs for KBDI are weather station latitude, mean annual precipitation, maximum dry bulb temperature, and the last 24 hours of rainfall. Reduction in drought occurs only when rainfall exceeds 5mm (0.20 inch) (called net rainfall).


Build Up Index
LOW
0.0-18.9
MOD
19.0-33.9
HIGH
34.0-53.9
V HIGH
54.0-76.9
EXTREME
77.0+

This index shows the amount of fuel available for combustion, indicating how the fire will develop after initial spread. It is calculated from the Duff Moisture Code and the Drought Code.

The BUI scale starts at zero and is open-ended. A rating above 34 is high, above 77 is extreme.


Initial Spread Index
LOW
0.0-3.9
MOD
4.0-7.9
HIGH
8.0-10.9
V HIGH
11.0-18.9
EXTREME
19.0+

This indicates the rate fire will spread in its early stages. It is calculated from the FFMC rating and the wind factor.

The open-ended ISI scale starts at zero and a rating of 10 indicates high rate of spread shortly after ignition. A rating of 19 or more indicates extremely rapid rate of spread.


Fine Fuel Moisture Code
LOW
0.0-80.9
MOD
81.0-87.9
HIGH
88.0-90.4
V HIGH
90.5-92.4
EXTREME
92.5+

This is a numerical rating of the moisture content of surface litter and other cured fine fuels. It shows the relative ease of ignition and flammability of fine fuels. The moisture content of fine fuels is very sensitive to the weather. Even a day of rain, or of fine and windy weather, will significantly affect the FFMC rating. The system uses a time lag of two-thirds of a day to accurately measure the moisture content in fine fuels. The FFMC rating is on a scale of 0 to 99. Any figure above 70 is high, and above 90 is extreme.


Forest Fire Danger Index
LOW
0.0-11.9
HIGH
12.0-24.9
VERY HIGH
25.0-49.9
SEVERE
50.0-74.9
EXTREME
75.0-99.9
CATASTROPHIC
100.0+

The Forest Fire Danger Index (FFDI) was developed in the 1960s by CSIRO scientist A.G. McArthur to measure the degree of danger of fire in Australian forests. The index combines a record of dryness, based on rainfall and evaporation, with meteorological variables for windspeed, temperature and humidity.

A FFDI of between 12 and 25 on the index is considered a "high" degree of danger, while a day having a danger rating of over 50 is considered an "Severe" fire danger rating. Above this level in 2010 a distinction was made between Forest and Grassland fuels. For Forest fuels, an FDI over 75 is categorised as "Extreme" and over 100 as "Catastrophic" (In Victoria the alternate rating name of "Code Red" has been adopted). For Grassland Fuels the threshold FDI values for the Extreme and Catastrophic Ratings was increased to 100 and 150 respectively.


Rainfall

Total Rainfall measurement for the previous 24 hours are utilized in several of the above calculations.