Weather Radar

The WSR-88D (NEXRAD) equipment at the Facility is a PUP associated with the actual radar at Mobile, AL (latitude 30°40'44" north and longitude 088°14'24" west).The height of the Mobile radar is 289' MSL.
a.NEXRAD helps identify sea breeze fronts before activity is visible on satellite images.To identify sea breeze fronts use either low elevations from Base Reflectivity or Composite Reflectivity products.The front will normally begin to appear northwest through northeast from the center of the radar in the non-precipitable range (below 18 dBz) of return as a thin line of radar return in the range of 1-14 dBz.

b.Severe weather detection with the NEXRAD is slightly different in the warm, moist, unstable air masses of the southeast region than it is in a region where the freezing level is generally lower.This makes the hail indicators on the NEXRAD fairly useless in the local region.One method in helping to detect for possible severe weather was researched at the Tampa, Florida radar site.It involves using a Vertically Integrated Liquid (VIL) Value of the Day (VOD) determined by the following formula:1500 ¸ (úT500ê+÷T400ê), where temperatures are in degrees Celsius.The formula for both analyzed and forecast temperatures is used at each level, with the average value from each equation used to determine the VIL Value of the Day.

For example:
500 temp = -11.7 ° C

400 temp = -24.3 ° C

forecasted500 temp = -13.9 ° C

forecasted400 temp = -26.1 ° C

1500 ¸ (11.7+24.3) =(don't forget to use absolute values)

1500 ¸ 36 = 41.67 » 42,

and1500¸ (13.9+26.1) =(these are the forecasted values)

1500 ¸ 40 = 37.5 » 38.

In the example above, the two values are averaged [(42+38) ¸ 2 = 40] to give you the VIL VOD of 40.

If there is a greater than 15 unit change in the VIL in one volume scan which then exceeds the VOD, investigate the storms further.If there is a greater than 20 unit change in the VIL in 2-3 volume scans which then exceeds the VOD, investigate the storms further.

When a VIL VOD is reached, it holds more significance if there is more than one pixel of high value.If there are four or more pixels just below the VIL VOD, investigate storms further.

When looking at reflectivity, a 50 dBz return or greater above 30,000' is a good indicator of possible severe weather.

When using the VIL product with tropical storms and hurricanes, maximum values are normally limited to the mid 20s, with the average values between 5 and 10.This helps in detecting embedded thunderstorm activity within the tropical storms.VILs ranging from approximately 15 to 25 are associated with the embedded activity.

Concept Mapping Toolkit
Insitute for Human and Machine Cognition
The University of West Florida