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.
NEXRAD helps identify sea breeze fronts before activity
is visible on satellite images through the use of 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.
Regional use of NEXRAD for severe weather detection 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.
In the local Pensacola area, the hail indicators on the NEXRAD are fairly
useless. One alternative method for detecting severe weather was researchedat
the Tampa, Florida radar site. It involves using a Vertically Integrated
Liquid (VIL) Value of the Day (VOD) determined by the following formula:
1500 ( ((T500(+(T400(), 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.
Storms should be investigated if there is a greater than
15 unit change in the VIL in one volume which then exceeds the VOD, or if there is a greater than 20 unit change
in the VIL in 2-3 volume scans which
then exceeds the VOD. However, if there are four or more pixels that are
just below the VIL VOD, would also be investigated, as the VIL VOD
has more significance if there is more than one pixel of high value.
For tropical storms and hurricanes, maximum values of
the VIL product are normally limited to the mid
20s, with the average values between 5 and 10. This helps
to detect embedded thunderstorm activity within the tropical storms, which
have associated VILs ranging from approximately 15 to 2.
A 50 dBz return or greater above 30,000' is a good indicator of possible