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Quality Warnings: 1.
Ozone: During Ozone Season
(from May through September), Georgia Environmental Protection Division
(GAEPD) along with other agencies in surrounding states will issue ozone
forecasts. When an area is forecast to
have high level of Ozone (defined as at or above Orange Class), Georgia
Forestry Commission will to stop issue burn permits for the area. The below statement will appear on the
weather forecast: “In corporation with the Georgia
Environmental Protection Division, the Georgia Forestry Commission will not
issue burning permits due to the high probability that open burning would
make an unacceptable contribution to ozone formation today for the following
counties, (listing of affected counties)” 2.
PM2.5 (Particulate Matter
smaller than 2.5 micrometer in size):
GAEPD along with other agencies in surrounding states are issuing
PM2.5 forecast year round. When an
area is forecast to have high level of PM2.5, the following statement will
appear on the weather forecast: “PM2.5 is forecast to be high (i.e. At or
Above Orange Class) for today for the following counties, (listing of
affected counties….” CAUTION
ITEM: The following statements
will show up if following conditions occurs:
Xth period is the period in
which the event is forecast to occur.
1st period is the 1st column in the
forecast. It is "Today" for
the morning forecast and "Tonight" for afternoon update. SKY
CONDITION: This
variable describes cloud amount, and how clouds may increase or
decrease. Tables 1 and 2 list the
adjectives used to describe sky condition. Table 1. Sky condition: The amount of cloud in the
forecast area for the period. The
following table is a list of descriptors used when
cloudiness stays the same in the period.
Table
2. If the cloudiness is forecast to
change during the period, the following descriptors are used.
TEMPERATURE: This is the extreme temperature (maximum or
minimum) expected for the forecast period.
Daytime maximum temperatures usually occur between 1-4pm. Nighttime minimum temperatures usually
occur at or near sunrise. RELATIVE
HUMIDITY: This is the extreme
relative humidity (maximum or minimum) expected for the forecast period. During the day, minimum relative humidities usually occur between 1-4pm. Nighttime maximum relativity humidity usually
occurs just before sunrise. HEAT INDEX: This is the heat index as
calculated by the National Weather Service.
It is based on temperature and humidity. The heat index category and effects are in
Table 3 and it is as used by National Weather Service. Table 3 Heat Index
category and effects
WIND CHILL
TEMPERATURE: This is the Wind Chill Temperature as
calculated by the National Weather Service.
It is based on temperature and wind speed. PROBABILITY OF PRECIPITATION: This is the probability of precipitation
expressed as a percentage. The phrases
associated with various probabilities are detailed in Table 4. Table 4.
Probability of Precipitation: The probabilities and associated phrases
associated with probability of precipitation.
PRECIPITATION
TYPE: The
type of precipitation such as showers, rain, thunderstorm, drizzle, snow, and
sleet. This line will not be in the
forecast if PROBABILITY OF PRECIPITATION is none. PRECIPITATION
AMOUNT: The
amount of precipitation in inches.
This line will not be in the forecast if PROBABILITY OF PRECIPITATION
is none. Forecast precipitation amount
of 2 inch or more is rare. PRECIPITATION
DURATION:
The length in hour of precipitation is expected to last. This line will not be in the forecast if
PROBABILITY OF PRECIPITATION is none. SURFACE
WINDS (OPEN):
Surface wind speed and wind direction in an open field at 20 feet. Special notes include variable and
occasionally gusty. Variable means
that wind direction will be variable and this usually occurs at wind speeds
of less than 5-7 MPH. Occasionally
gusty means that wind speed will be occasionally gusty and this is usually
associated with frontal passage. WIND
SPEED INCREASE WITHIN PERIOD: For the
periods in which the event occurs, this field indicates the beginning and
ending wind speed. For the periods in
which the event does not occur, "None" will appear in the field. If this event is not forecast in any of the
periods, this line will not appear in the forecast. WIND
DIRECTION SHIFT WITHIN PERIOD: For the
periods in which the event occurs, this field indicates the beginning and
ending wind direction and whether it is a clockwise or counter-clockwise
shift. For the periods in which the
event does not occur, "None" will appear in the field. If this event is not forecast in any of the
periods, this line will not appear in the forecast. CANOPY
WINDS:
Expected wind speed and wind direction inside a forest. It is assumed this wind is representative
of a pine stand of basal area 100, with no more than a 3-year rough. THE
SMOKE DISPERSION INDEX: The smoke dispersion index is a measure of the atmosphere’s
"diluting power". Values are
relative in that an index of 48 would suggest that the atmosphere should be
able to take twice the smoke as would be possible for an index value of 24.
The atmosphere over a district or county can be viewed as a covered cake pan
in simplistic terms. Even if the dispersion in this cake pan were good, it
would still be possible to saturate the container with too much smoke. This
index SHOULD NOT BE USED ALONE in the deciding whether to initiate or approve
a burn. Description and interpretation
of the range of smoke dispersion values can be found in Table 5. Caution should be used in initiating or
permitting burns when daytime values are below 40. No two
cases are ever exactly alike. Thus,
some reasonable judgment and common sense needs to be applied. The dispersion
index as used in the GFC fire weather forecast is valid for the middle of the
daytime periods and from the middle to last half of the nighttime periods. Because the
daytime dispersion index given is, say 50, does NOT mean that the dispersion
index starts out at 50 for the given forecast period. There is a "time
window" during the 12‑hour forecast period when, if the forecast
is correct, this dispersion index should be at or near 50. At sunrise,
dispersion is low normally. As the sun gets higher and induces more heating,
the dispersion index will climb. At first, the amount of improvement will be
minimal. About 3 or 4 hours after sunrise, the amount of improvement should
be significant. On average, the best dispersion will be in the early to mid‑afternoon.
After this period, dispersion will start to degrade and towards sunset, it
should drop like a "rock". Each case will be somewhat different as
many factors enter into the equations. Table
5. Atmospheric Dispersion Index (ADI)
values for daytime and nighttime burns.
(Table 5.2.5/5.2.6 of NWCG
Smoke Management Guide for Prescribed Fire, 2020)
FOG
POTENTIAL: This is an experience
based estimation of the potential for natural fog. It
is a function of cloud cover, probability of precipitation, relative humidity,
and wind speed. LOW
VISIBILITY OCCURRENCE RISK INDEX : The Low Visibility Occurrence
Risk Index (LVORI) was developed based on
From
operational experience, one should be VERY
CAUTIOUS ABOUT BURNING if one of the following situations occurs: 1. When LVORI for a nighttime forecast period
is 8,9 or 10 2. When ACTIVE SMOKE from stumps logs, etc. is
present during the night 3. When
there is a roadway within three miles of a burn site with open fields,
logging roads, or open streams that can provide an easy transit of the smoke
from the burn site to the roadway Although
not as dangerous as an index value from 8 to 10, LVORI of 6 or 7 should be treated
with caution if there is active smoke produced during the night, and the burn
site is near a roadway. NWS
at Greenville/Spartanburg has an informative
page on LVORI and Dispersion Index. MIXING
HEIGHT:
The mixing height is the thickness of the lower layer of the atmosphere where
"mixing" occurs. Usually, it
is in the order of a few thousand-feet during the day and on the order of a
few hundred-feet at night. . It is available in the forecast as both metric
and non‑metric units. Most federal Environmental Protection Agency’s
(EPA) models use the metric values. In general,
mixing height will be highest during daytime periods and lowest during
nighttime periods. Heating, winds, etc. are some of the factors that
determine how thick the mixing layer will become. During the
daytime, mixing height will be lowest at sunrise and should reach maximum
thickness by mid‑day. The thickness of this layer will normally
decrease fairly quickly as sunset approaches.
Daytime values below 1700 feet are generally associated with poor
smoke dispersion. A
simplistic analogy would be the afternoon and evening thunderstorms that
commonly occur in the south during the summer. As the maximum heating of the
day approaches, the clouds start to boil upwards and eventually may form
thunderstorms. Assuming no other potential influences (fronts, etc.), as
sunset approaches, the heating that drives these thunderstorms is shut off.
Often times, these
thunderstorms will begin to dissipate soon after sunset. TRANSPORT
WIND SPEED:
This is the averaged of all wind speeds between the surface and the mixing
height. Spotting and suspended
particles from burning are typically transported at this speed. It is
available in the forecast as both metric and non‑metric values. Most of
EPA’s models use metric values. TURNER STABILITY AND ATMOSPHERIC TENDENCY -Turner stability (Turner
1961) is a measure of atmospheric stability with values ranging between 1 and
7. By
definition, Turner values of 1, 2 or 3 are possible only during daytime
periods and values of 5, 6 or 7 are only possible during nighttime periods. A
Turner value of 4 is possible both during the day and night. Table 6 summarizes the relationship between
Turner stability class and expected fire behavior. Table
6. Turner Stability Class (Pasquill Stability Class): It is computed as a function
of ceiling height, solar radiation, day/night period and
wind speed. Turner (1961)
PLUME TRAJECTORY - This is the direction that a smoke plume
is expected to travel. If the plume trajectory were north, the smoke would be
moving toward the north, implying southerly winds. Trajectory as used by the Georgia Forestry
Commission system will always imply the direction in which something is
going. Wind directions on the other hand are the direction from which the
winds are coming from. DRYING
POTENTIAL: Drying potential is a function of estimated pan
evaporation. Saturation vapor
pressure, vapor pressure, and evaporation are computed by equations ported
from the Table 7. Drying Potential adjective and associated evaporation.
AVAILABLE
SUNSHINE:
The number of hours of sunshine |