850 mb Heights and Temperature
model mode
This panel shows the
850 mb forecasted fields for geopotential
height, temperature and wind vectors.
850 mb charts depict conditions in the lower troposphere (roughly 1500 meters).
Geopotential
height approximates the actual height of a pressure surface
above mean sea-level and is represented by the solid white contours.
The geopotential height field is given in meters with an interval of 30
meters between height lines. The locations of surface
cyclones and
anticyclones hold similar
positions in the 850 mb geopotential height field.
Wind
vectors provide information about wind direction and wind
speed and are drawn here as tiny purple arrows. Wind vectors point towards the
direction in which the wind is blowing
and the longer the wind vector, the stronger the wind. The unit of magnitude
for wind speed as depicted by the wind vectors is meters per second.
Temperature is represented by the color filled regions and the associated
values are indicated by the color code located in the
lower left corner of the forecast panel. Temperatures are given in
degrees Celsius with an interval of 5 degrees Celsius
between temperature contours, also called
isotherms.
In this particular image, the important features are
the deep low over the Northern Great Plains. Warm air
is being transported on the east side of the low, while cold air is being
transported on the west side of the low. Snow is likely to fall in
the western Dakotas and eastern Montana since the temperature is below
freezing in these locations.
Temperature at 850 mb does not
experience the diurnal variation as seen at the surface, so this is a good
indicator where warm air and cold air is located.
Precipitation type can also be estimated from the 850 mb temperature field.
Snow is likely to occur where the 850 temps are below freezing (zero and below),
while liquid precipitation is found at warmer temperatures.
Also, vertical motion occurs in the presence of
temperature advection.
Warm advection causes upward motion, while
cold advection causes downward motion.
Finally, if cold advection occurs underneath an upper level
trough, then the trough will amplify and strengthen a
surface cyclone.
850 hghts, humidity
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1000 convrg & temp
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