Interested in MeteoMaps(tm)? Below are frequently asked
questions and descriptions of the specific MeteoMaps offered. If you
have a question that we didn't answer,
let us know!
Surface MeteoMaps
- National Maps
The National Maps
include a temperature and pressure map for the United States.
The temperatures are contoured every 10 degrees and the pressure
is contoured every 4 millibars.
- Regional Station Model Plots
The
Station Model Plot includes plotted temperature, visibility,
weather, dewpoint, pressure, pressure tendency, and 6 hours of
precipitation observations. The station model is centered around
a circle which indicates cloud cover. The station model format
is shown at the bottom of the graphic. The codes are explained
below:
| TMP |
Temperature shown in degrees
Fahrenheit. |
| VIS |
Visibility given in miles. |
| OBS |
Weather symbol for type of
precipitation |
| DEW |
Dew point shown in degrees
Fahrenheit |
| PRS |
Pressure given in millibars with
the leading 9 or 10 omitted |
| PRS-TEND |
3-hour Pressure Tendency shown
in tenths of a millibar |
| PREC |
Precipitation for the last 6
hours |
| CC |
Cloud cover: No lines in the
circle indicate a clear sky, one vertical line indicates
scattered clouds (1 to 5 tenths), two vertical lines are used
for broken clouds (6 to 9 tenths). A plus symbol, +, indicates
high overcast skies; an X indicates obscured sky; an asterisk
(*) inside a circle indicates low overcast skies. |
Upper Air MeteoMaps
- National Upper Air Maps, Analyzed
These maps give specific information plots from selected upper
air stations for each atmospheric pressure level. Data from all
stations is analyzed every 30 meters for heights and every 5
degrees for temperatures. The station model format is shown at
the bottom of the graphic. The codes are explained below:
| TEMP |
Temperature shown in degrees
Fahrenheit. |
| HGT |
Heights in meters (decameters
500 millibar and above) |
| HGT-T |
12-hour height tendency in
meters (decameters 500 millibar and above) |
| DEWP-DEP |
Dew point depression in tenths
of degrees Celsius. |
- National Thickness Maps, Analyzed
These maps show the thickness in meters of the atmosphere
between either the 1000 millibar and 500 millibar levels or the
1000 millibar and 850 millibar levels, analyzed every 9 meters.
Sounding Plots
- Soundings (SKEW-Ts)
A sounding
comprises a vertical picture of the atmosphere which is a
helpful tool in determining the stability of the atmosphere,
type of precipitation, and maximum temperature. Pressure levels
are shown on the left side of the sounding corresponding to
horizontal lines across the diagram. Temperature (in degrees
Celsius) is shown at the bottom of the diagram, with
temperatures lines running diagonally (or skewed) across the
diagram. Also provided is mixing ratio information, plotted wind
barbs, and many thermodynamic variables (see below for a list).
| LCL |
Lifting Condensation Level
- Height at which a parcel of air becomes saturated when it is
lifted dry adiabatically. |
| CCL |
Convective Condensation
Level - Height at which a parcel of air, if heated
sufficiently from below, will rise adiabatically until
condensation occurs. It is the height of the base of cumuliform
clouds which are or would be produced by thermal convection
solely from surface heating. Severe weather usually occurs when
the CCL is at or below 770 millibars. |
| LFC |
Level of Free Convection
- The height at which a parcel of air lifted dry adiabatically
until saturated, and saturated adiabatically thereafter would
first become warmer than the surrounding air, and then continues
to rise until it becomes colder than the surrounding air. Severe
weather usually occurs when the LFC is at or below 650
millibars. |
| FL |
Freezing Level - Height
at which temperature is at freezing. |
| WBO |
Wet Bulb Zero Height -
Height where wet bulb reaches zero. Generally, if the wet bulb
zero height ranges between 7,000-9,000 feet, large hail,
damaging winds, and tornadoes are possible. At the Gulf Coast,
the range must be between 9,000-10,500 feet for damaging winds
and hail to occur. |
| EL |
Equilibrium Level -
Height where the temperature of a buoyantly rising parcel of air
again becomes equal to the temperature of the surrounding air.
Usually, if thunderstorm echo heights are above this equilibrium
level, it is referred to as 'Over-Shooting Tops' and is a
precursor to severe weather. |
| KI |
K-Index - Stability
index useful in predicting non-frontal thunderstorm situations.
Relationship of K-Index to probability of thunderstorms: K
15-20: < 19%, K 21-25: 20-39%, K 26-30: 40-59%, K 31-35:
60-9%, K 36-40: 80-89%, K >40: >90%. |
| LI |
Lifted Index - This
index helps predict overall atmospheric stability. Lifted Index
guidelines: +3 to +1: slightly unstable, supports showers, +1 to
-1: unstable, supports showers and isolated T-storms, -1 to -3:
moderately unstable, supports widespread T-storms, -3 to -6:
very unstable, supports severe T-storms, <-6: extremely
unstable, supports widespread severe weather. |
| SSI |
Showalter Index - A
stability index similar to the Lifted Index, but values are
typically not as low for severe weather. Generally, an index of
+3 to +1 supports T-storms and <-3 supports severe weather.
|
| SI |
Sweat Index - Stability
index indicating severe T-storms and tornado potential. |
| CTI |
Cross Totals Index -
This index determines the horizontal transport of unstable air.
A value in excess of 25 is needed for strong T-storms. |
| VTI |
Vertical Totals Index -
This index determines the vertical transport of unstable air.
Values in excess of 25 are needed for strong T-storms. |
| TTI |
Total Totals Index -
This index determines the potential for T-storms and is very
helpful in diagnosing the difference between weak and strong
T-storms. The relationship between the TTI and Thunderstorm
Acitivity is as follows: 44 - Spotty, usually light
thunderstorm. 46 - Spotty, usually moderate thunderstorm. 48 -
Usually heavy thunderstorm. 50 - Usually heavy thunderstorm with
hail possible. 52 - Usually heavy thunderstorm with a tornado
possible. 56 - Heavy thunderstorm with tornadoes likely. |
| EPA |
Positive Area - Positive
area denotes the buoyancy of the atmosphere. The higher the
positive area, the more buoyant energy available. Values in
excess of 500J/KG support T-storms, values between 1000 and 3000
J/KG support T-storm development with moderate shear. |
| PW |
Precipitable Water - The
amount of water that would be found in a column of air above the
surface. Comparing sounding values indicates the amount of water
available for rain or snowfall potential. |
| TH |
Tropopause Height -
Height where the tropopause begins, or the temperature curve
warms. The location of a tropopause height helps determine
severe T-storm potential. If T-storm echo tops exceed tropopause
height, severe weather is likely. |
| STC |
Convective Temperature -
The surface temperature that must be reached to begin formation
of convective clouds by solar heating of the surface air layer.
|
| HSZ |
Hail Size - The size
that hail may reach given the state of atmospheric updrafts.
This is based on the calculation of critical updraft speed which
determines the size of hailstones that can stay aloft for a
given updraft speed. |
| STC |
Richardson Shear Index -
This value indicates how turbulent the flow is. Low RI numbers
are associated with fast moving systems in an environment that
has strong shear. Small RI numbers support greater shear. |
Computer Model Forecasts
- European Model Data (ECMWF)
European World Model
Output Forecasts extend out to 6 days. The U.S. maps presented
here include Surface Pressure analyzed every 4 millibars, 500
millibar heights analyzed every 40 meters, and 1000-500 millibar
Thickness analyzed every 40 meters.
- High Resolution Computer Model Data
This data
comes from the National Weather Service's NGM or ETA weather
forecast models. Utilizing 00z or 12z data, these maps show a
combination of Surface Pressure analyzed every 4 millibars,
1000-500 millibar Thickness analyzed every 60 meters, and wind
barbs.
- MOS Temperature Data
MOS (Model Output
Statistics) data is produced by the National Weather Service's
NGM model. MOS maps include predicted High and Low Temperatures
for selected U.S. cities for the next 3 days, in Fahrenheit,
analyzed every 10 degrees.
- RUC Computer Model Data Plots
The RUC (Rapid
Update Cycle) model forecasts 12 hours into the future in 3-hour
increments. The RUC maps include Surface Pressure analyzed every
4 millibars, Surface Temperature analyzed every 5 degrees
Celsius, 850 millibar Temperature analyzed every 5 degrees
Celsius, and Convective Precipitation in Inches.
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