EXAMPLE 2:  FLOOD EVENT

2201 UTC 22 July 2001

This KMLB WSR-88D reflectivity image was taken at the time a flood warning was issued for the area north and northeast of Orlando. Two inches of rain had already fallen in a short period of time, and persistent heavy rains threatened an additional 1-2 inches (see Table 1). The corresponding image from LDIS (below) depicts a stationary cyclonic shear axis and zone of high buoyancy stretching from a surface over the Gulf of Mexico west of Tampa. The boundary extended inland near a line from Tampa to Orlando to Daytona Beach. South to southwest winds of 10 to 15 mph were advecting a very moist airmass northward toward the convergence boundary. Surface METAR observations and KMLB WSR-88D Level II reflectivity and radar velocity data were ingested into the analyses, however FAWN observations were not yet available.
 
 
 
 
 
 
 
 
 
 

0202 UTC 23 July 2001

This KMLB WSR-88D reflectivity image was taken 4 hours after the previous image. By this time the persistent band of convection which earlier affected central Florida had mostly dissipated, with only a patch of light rain and a few isolated heavier showers remaining north and west of Orlando. The corresponding LDIS analysis (below) indicated the shear axis had become less defined and had lifted northward. Southerly winds feeding into the boundary had weakened to 5-10 mph. Buoyancy values had decreased to near 1000 J/kg across the previous flood warning area as surface heating ceased.

The depiction of the shear axis anchored just south of the convective band, within a region of CAPE maxima, suggested the heavy rainfall would persist across the central Florida interior.

Note: this LDIS event occurred prior to the ingestion of FAWN surface observations, however KMLB WSR-88D Level II reflectivity and radial velocity data were used in the analyses.
 
 
 
 
 

Table 1. Flood Warning for portions of east central Florida near the boundary.

BULLETIN - EAS ACTIVATION REQUESTED FLOOD WARNING NATIONAL WEATHER SERVICE MELBOURNE FL 605 PM EDT SUN JUL 22 2001 THE NATIONAL WEATHER SERVICE HAS ISSUED A * FLOOD WARNING FOR...   NORTHERN ORANGE COUNTY   SEMINOLE COUNTY   IN EAST CENTRAL FLORIDA * UNTIL 800 PM EDT * AT 605 PM EDT...WEATHER SERVICE DOPPLER RADAR AND SPOTTER REPORTS INDICATED HEAVY RAIN CONTINUING OVER ALTAMONTE SPRINGS TO WINTER PARK AND OVIEDO WITH A SLOW DRIFT TO THE WEST. * THUNDERSTORMS WITH EXCESSIVE RAINFALL WILL CONTINUE OVER MUCH OF SEMINOLE AND NORTHERN ORANGE COUNTY WITH TOTAL RAINFALL AMOUNTS OF 3 TO 4 INCHES POSSIBLE. A SPOTTER IN CASSELBERRY RECENTLY REPORTED 2 INCHES OF RAIN IN A HALF HOUR. EXCESSIVE RUNOFF FROM THIS STORM WILL CAUSE FLOODING OF SMALL CREEKS AND STREAMS...HIGHWAYS AND UNDERPASSES. ADDITIONALLY...OTHER LOW LYING AREAS ARE SUBJECT TO FLASH FLOODING. A FLOOD WARNING MEANS THAT FLOODING IS IMMINENT OR OCCURRING.  PERSONS LIVING ALONG STREAMS AND CREEKS SHOULD TAKE IMMEDIATE PRECAUTIONS TO PROTECT PROPERTY. DO NOT ATTEMPT TO CROSS SWIFTLY FLOWING WATERS OR WATERS OF UNKNOWN DEPTH BY FOOT OR BY AUTOMOBILE. IF YOUR VEHICLE STALLS ABANDON IT IMMEDIATELY AND SEEK HIGHER GROUND. TO REPORT SEVERE WEATHER HAVE THE NEAREST LAW ENFORCEMENT AGENCY RELAY YOUR REPORT TO THE NATIONAL WEATHER SERVICE FORECAST OFFICE.