Element
Definitions
8- TO 14-DAY AVERAGE TEMPERATURE ABOVE
NORMAL is the probability,
expressed as a percent, of above normal (median) categories
of 7-day mean temperature at a lead-time of 1 week.
8- TO 14-DAY AVERAGE TEMPERATURE BELOW
NORMAL is the probability,
expressed as a percent, of below normal (median) categories
of 7-day mean temperature at a lead-time of 1 week.
8- TO 14-DAY TOTAL PRECIPITATION ABOVE
NORMAL is the probability,
expressed as a percent, of above normal (median) categories
of 7-day total precipitation at a lead-time of 1 week.
8- TO 14-DAY TOTAL PRECIPITATION BELOW
NORMAL is the probability,
expressed as a percent, of below normal (median) categories
of 7-day total precipitation at a lead-time of 1 week.
12-HOUR PROBABILITY
OF PRECIPITATION PoP12 is the likelihood, expressed
as a percent, of a measurable precipitation event (1/100th
of an inch or more) at a grid point during the 12-hour
valid period. The 12-hour valid periods begin and end at
0000 and 1200 Coordinated
Universal Time (UTC).
APPARENT TEMPERATURE is the
perceived temperature in degrees Fahrenheit derived from
either a combination of temperature and wind (Wind Chill)
or temperature and humidity (Heat Index) for the indicated
hour. When the temperature at a particular grid point falls
to 50°F or less, wind chill will be used for that point
for the Apparent Temperature. When the temperature at a grid
point rises above 80°F, the heat index will be used for
Apparent Temperature. Between 51 and 80°F, the
Apparent Temperature will be the ambient air temperature.
CATEGORICAL CONVECTIVE
HAZARD OUTLOOK is a categorical forecast
(slight, moderate, or high risk)
that
specifies the perceived level of threat of thunderstorms,
severe thunderstorms, hail, damaging winds, and tornadoes.
DEW POINT is the expected dew
point temperature in degrees Fahrenheit for the indicated
hour. Dew point temperature is a measure of atmospheric moisture. It
is the temperature to which air must be cooled in order to
reach saturation (assuming air pressure and moisture content
are constant).
HAZARDS are weather or hydrologic hazardous events issued
for the protection of life and property and the enhancement
of the national economy. For a specific list of hazards
available through NDFD, see the Product Description Document
entitled “Experimental
Hazard Grids in the National Digital Forecast Database”,
Appendix A.
MAXIMUM/MINIMUM
TEMPERATURE is the daytime maximum or the overnight minimum temperature
in degrees Fahrenheit.
ONE-MONTH AVERAGE TEMPERATURE ABOVE
NORMAL is the probability,
expressed as a percent, of above normal (median) categories
of one-month mean temperature at a lead-time of ½-month.
ONE-MONTH AVERAGE TEMPERATURE BELOW
NORMAL is the probability,
expressed as a percent, of below normal (median) categories
of one-month mean temperature at a lead-time of ½-month.
ONE-MONTH TOTAL PRECIPITATION ABOVE
NORMAL is the probability,
expressed as a percent, of above normal (median) categories
of one-month total precipitation at a lead-time of ½-month.
ONE-MONTH TOTAL PRECIPITATION BELOW
NORMAL is the probability,
expressed as a percent, of below normal (median) categories
of one-month total precipitation at a lead-time of ½-month.
PROBABILISTIC
TROPICAL CYCLONE SURFACE WIND SPEED (CUMULATIVE) is
the probability (in percent) of sustained surface wind
speed greater than 34-, 50- and 64-knots (3 separate elements)
sometime during the specified cumulative forecast period
(0 – 6
hours, 0-12, 0-18, etc.) at each specific point. NOTE:
This element is provided for coastal and inland points
as well as offshore locations (e.g., buoys).
PROBABILISTIC
TROPICAL CYCLONE SURFACE WIND SPEED (INCREMENTAL) is
the probability (in percent) of sustained surface wind
speed greater than 34-, 50-, and 64-knots (3 separate elements)
sometime during the specified forecast period (0 - 6 hours,
6 -12, 12 -18, etc.) at each specific point. These values
are incremental since they can increase in value by accounting
for the possibility the event might start in an earlier
period and still be occurring in the specified period.
NOTE: This element is provided for coastal and inland points
as well as offshore locations (e.g., buoys).
PROBABILITY
OF DAMAGING THUNDERSTORM WINDS is the probability
(in percent) of winds greater than 58 miles per hour occurring
within 25 miles of any point during the outlook period.
The higher the probability, the higher the threat of severe
thunderstorm winds occurring.
PROBABILITY OF
EXTREME HAIL is the probability (in percent)
of hail greater than 2 inches in diameter within 25 miles
of any point during the outlook period. The higher the
probability, the higher the threat of extreme hail occurring.
PROBABILITY
OF EXTREME THUNDERSTORM WINDS is the probability
(in percent) of winds greater than 75 miles per hour occurring
within 25 miles of any point during the outlook period.
The higher the probability, the higher the threat of extreme
thunderstorm winds occurring.
PROBABILITY
OF EXTREME TORNADOES is the probability (in percent)
of Enhanced
Fujita scale 2 (EF2) tornadoes occurring within 25
miles of any point during the outlook period. The higher
the probability, the higher the threat of extreme tornadoes.
PROBABILITY OF HAIL is
the probability (in percent) of hail greater than three-quarters
of an inch in diameter (size of a penny) occurring within
25 miles of any point during the outlook period. The higher
the probability, the higher the threat of severe hail.
PROBABILITY OF
TORNADOES is the probability (in percent) of
a tornado occurring within 25 miles of any point during
the outlook period. The higher the probability, the higher
the threat of tornadoes occurring.
QUANTITATIVE PRECIPITATION
FORECAST (QPF) is the expected amount of liquid
precipitation (in hundredths of inches) accumulated over
a six hourly period. A QPF will be
specified when a measurable ( 1/100th of an inch or more)
precipitation type is forecast for any hour during a QPF
valid period. NDFD valid periods for QPF are 6 hours
long beginning and ending at 0000, 0600, 1200 and 1800
UTC.
RELATIVE HUMIDITY is a ratio, expressed as a percent, of the amount of atmospheric
moisture present relative to the amount that would be present
if the air were saturated. Since the latter amount
is dependent on temperature, relative humidity is a function
of both moisture content and temperature.
SIGNIFICANT WAVE
HEIGHT is the average height in feet (from trough
to crest) of the one-third highest waves for the indicated
12-hour period. The 12-hour periods begin and end at 0000
and 1200 UTC.
SKY COVER is the expected
amount of opaque clouds (in percent) covering the sky valid
for the indicated hour.
SNOW AMOUNT is
the expected total accumulation of new snow (in inches) during
a 6 hour period. A snow accumulation grid will be specified whenever
a measurable snowfall is forecast for any hour during a valid
period. Valid periods for the NDFD begin and end at 0600,
1200, 1800, and 0000 UTC.
TEMPERATURE is the expected
temperature in degrees Fahrenheit valid for the indicated
hour.
THREE-MONTH AVERAGE TEMPERATURE ABOVE
NORMAL is the probability,
expressed as a percent, of above normal categories of 3-month
mean temperature at lead-times ranging from ½-month
to 12-1/2 months.
THREE-MONTH AVERAGE TEMPERATURE BELOW
NORMAL is the probability,
expressed as a percent, of below normal categories of 3-month
mean temperature at lead-times ranging from ½-month
to 12-1/2 months).
THREE-MONTH TOTAL PRECIPITATION ABOVE
NORMAL is the probability,
expressed as a percent, of above normal categories of 3-month
total precipitation at lead-times ranging from ½-month
to 12-1/2 months.
THREE-MONTH TOTAL PRECIPITATION BELOW
NORMAL is the probability,
expressed as a percent, of below normal categories of 3-month
total precipitation at lead-times ranging from ½-month
to 12-1/2 months.
TOTAL PROBABILITY
OF EXTREME SEVERE THUNDERSTORMS is the
probability in percent of EF2 (Enhanced
Fujita scale 2) tornadoes, damaging winds
with speeds greater than 75 miles per hour, or large hail
two inches or greater in diameter occurring within 25 miles
of any point during the outlook period.
TOTAL PROBABILITY
OF SEVERE THUNDERSTORMS is the probability in
percent of tornadoes, damaging winds with speeds greater
than 58 miles per hour, or large hail three quarters of
an inch in diameter (penny-size) occurring within 25 miles
of any point during the outlook period.
WEATHER is the expected weather
(precipitating or non-precipitating) valid at the indicated
hour. Precipitating weather includes type, probability, and
intensity information. In cases of convective weather, coverage
may be substituted for probability.
WIND DIRECTION is the expected
sustained 10-meter wind direction for the indicated hour,
using 36 points of a compass. Click here for
information on interpreting wind barbs.
WIND GUST is
the maximum 3-second wind speed (in knots) forecast to occur
within a 2-minute interval at a height of 10 meters. Wind
gust forecasts are valid at the top of the indicated hour.
WIND SPEED is the expected
sustained 10-meter sustained wind speed (in knots) for the
indicated hour.
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