Here is a check-list that you can refer to
when making your forecasts.
Print it and/or refer to it often.
- Will cloud cover play an important role in your
temperature forecast? (more info...)
Cloudiness during the day blocks sunshine and tends to keep temperatures cool. Nighttime
cloudiness keeps surface heat from escaping into the atmosphere, which makes overnight
temperatures warmer. The thicker the clouds, the more effect it will have.(
Close)
- Will temperature advection play an
important role in your temperature forecast? (more info...)
If the winds at the surface or at 850 mb are blowing from an area with much warmer or cooler
temperatures (across the contour lines on a temperature map), then it will help to move that airmass
into your location. If the winds are strong enough (greater than 10 or 15 knots), this could have a
significant warming or cooling effect on your temperatures.
(
Close)
- Will fronts
play an important role in your temperature forecast? (more info...)
If a cold front moves through your location, you can expect cooler temperatures behind it. Any
precipitation will usually occur in close vicinity of the front. If a warm front
moves through, expect warmer air behind it. Any precipitation will occur only on the north side of the front, but
over a large area. Stationary fronts can sometimes cause precipitation, but they will not affect your temperature
forecast unless they are very close to your location. (
Close)
- Is
there sufficient moisture (from surface to 850 mb) for precipitation to
occur? (more info...)
- If there is moisture available, is there a forcing mechanism
to lift it?
Dew point is a good indicator for the amount of moisture in the atmosphere. If there is less than a 10 degree
Celsius difference (about 18 degrees Fahrenheit) between the air temperature and the dew point temperature, then
you would consider there to be sufficient moisture for precipitation. Relative humidity (RH) may also be used. In
order for precipitation to occur, however, this air has to be lifted for the moisture to condense. Good
forcing mechanisms include but are not limited to fronts, vorticity, divergence in the upper atmosphere, and
convergence near the surface. (
Close)
- Is there vorticity at 500 mb? (more info...)
Vorticity refers to a type of rotating motion in the atmosphere. The movement of high and low areas of vorticity at
500 mb can be a good indicator for where upward and downward motion will occur. If an area of high vorticity will
moving into your location in the next 12 hours or so, then you can expect upward motion to occur ahead of it.
Conversely, if an area of low vorticity is approaching, then you will experience downward motion. (
Close)
- Are there any short waves at 700 mb? (more info...)
Short waves can be observed as small "kinks" in the flow of the atmosphere (look at the contour lines to find
where they are). You can expect upward motion to occur
in areas where these are located. (
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- Is
the jet stream at 300 mb positioned for development? (more info...)
If you divide the area of highest winds in the jet stream into four quadrants, the left front and right rear
sections are the most favorable areas for upward motion and precipitation to occur. The right front and left rear
sections support downward motion and are not good for precipitation. (
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Starred * links
are particularly useful at the beginning of the semester.
Updated: 19 Jan 2005
Send comments and suggestions to:
Heather Moser
miraje@iastate.edu
