Meteorology 415
Predicting Surface Visibility
Fall 2011
Name: _________________________
When considering the forecast of surface visibility, you would naturally think that the difference
between the dry bulb and dew point temperature combined with the wind speed would be a fine
correlation with reduced surface visibility:
Fog Forecasting for the Southern Region: A Conceptual Model Approach
Paul J. Croft - Jackson State University, Jackson, Mississippi
Given the graphs above, estimate the likelihood of warm advection fog formation at the following site:
LAKE CHARLES, LA
Sea Temperature – 61F
12:53 AM
1:53 AM
2:53 AM
3:17 AM
62.1 °F
63.0 °F
63.0 °F
64.4 °F
61.0 °F
61.0 °F
61.0 °F
62.6 °F
96%
93%
93%
94%
29.90 in
29.89 in
29.88 in
29.86 in
8.0 miles
9.0 miles
6.0 miles
6.0 miles
SSE
SSE
SSE
SSE
9.2 mph
8.1 mph
6.9 mph
6.9 mph
- N/A
- N/A
- N/A
- N/A
Overcast
Overcast
Overcast
Overcast
Probability of <2 miles in Fog by 7am LST: ____________________________ (remember the units!)
Sea Temperature- 58F
12:53 AM
1:53 AM
2:53 AM
3:53 AM
4:53 AM
44.1 °F
45.0 °F
45.0 °F
45.0 °F
45.0 °F
41.0 °F
41.0 °F
41.0 °F
39.9 °F
39.0 °F
89%
86%
86%
82%
80%
30.26 in
30.25 in
30.23 in
30.22 in
30.21 in
9.0 miles
9.0 miles
9.0 miles
10.0 miles
10.0 miles
NE
East
ESE
ESE
ESE
4.6 mph
5.8 mph
5.8 mph
8.1 mph
9.2 mph
- 0.00 in
- 0.00 in
- 0.00 in
- N/A
- N/A
Overcast
Rain Light Rain
Overcast
Overcast
Overcast
Probability of <2 miles in Fog by 7am LST: ____________________________ (remember the units!)
There are a variety of processes for fog formation (Myers, 1968J.N. Myers, Fog, Sci. Am. 219 (1968), pp.
75–82.) They can be seen in the diagram below:
Precipitation induced fog and warm advection over a cold ground/snow cover (not shown) are perhaps
the most challenging types.
The properties of fogs differ particularly between radiation and advection fog types:
Review the satellite/surface map combinations below and determine which process caused the fog.
PROCESS: ____________________
1645Z
PROCESS: __________________
12Z
1445Z
Other restrictions to visibility are seen in the table below:
Studies on blowing snow have shown that the wetness of the snow determines that threshold wind
speed needed for blowing snow to occur. Wet snow being defined as at temperatures between
26-32F.
Estimates of Threshold Wind Speeds for Snow Transport Using Meteorological Data
LONG LI
Division of Hydrology, University of Saskatchewan, Saskatoon, Saskatchewan Canada
With the above criteria, review the two MOS forecasts for temperature and wind to determine what
frequency the snow on the ground would become airborne.
Blowing Snow Frequency: FAR: _____________
BUF: ______________________
USING SATELLITE IMAGERY TO ESTIMATE SURFACE VISIBILITY…..
From this recent visible satellite picture, determine the approximate surface visibility at the following
sites:
Caribou, ME : ___________
Boston, MA: ____________
Erie, PA: ________________
Chicago, IL: ______________
Elkins, WV: ______________
Green Bay, WI: ____________