Thunderstorms developed across western Nebraska and moved into south central Nebraska Monday evening and night.  Damaging thunderstorm wind gusts were the most common hazard from the storms, although large hail was also reported.  As the storms weakened, heat bursts developed, which caused temperatures to jump to the upper 70s to near 80 degrees, and the wind to gust to 40-60 mph.

Heat bursts are caused by decaying thunderstorms and develop in a unique environment.  The setup for a heat burst requires dry air directly beneath a weakening elevated thunderstorm.  When a thunderstorm is weakening, air within the thunderstorm begins to sink.  If the sinking air is very dry and high enough, it will begin to accelerate toward the ground since it is more dense.  Any remaining precipitation will fall through the dry air and evaporate.  As the air continues downward, it warms rapidly due to compression. 

The following image depicts the temperature and relative humidity profile at the Regional Airport in Grand Island, NE.  As the rain arrived, the relative humidity increased, and then the relative humidity dropped, and the temperature rose with the heat burst which occurred shortly after 2 am CDT (0702 UTC).   The graphic is courtesy of MesoWest.


Preliminary storm reports from Monday evening and night are listed below.

 

.TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON  
   
.DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE.  
  
            ..REMARKS..  
  
0721 PM     TSTM WND GST     4 S GOTHENBURG          40.87N 100.16W  
07/14/2008  E60.00 MPH       DAWSON             NE   TRAINED SPOTTER   
  
0723 PM     TSTM WND GST     WILLOW ISLAND           40.88N 100.07W  
07/14/2008  E70.00 MPH       DAWSON             NE   TRAINED SPOTTER   
  
            60 TO 70 MPH WINDS  
  
0818 PM     HAIL             5 NW KEARNEY            40.75N 99.15W   
07/14/2008  E0.75 INCH       BUFFALO            NE   TRAINED SPOTTER   
  
            MEASURED 42 MPH WIND GUST  
  
0818 PM     HAIL             LITCHFIELD              41.16N 99.15W   
07/14/2008  E1.00 INCH       SHERMAN            NE   PUBLIC            
  
0826 PM     HAIL             8 WNW KEARNEY           40.74N 99.23W   
07/14/2008  E1.00 INCH       BUFFALO            NE   STORM CHASER      
  
            52 MPH MEASURED WIND GUST WITH THE QUARTER SIZE HAIL  
  
1240 AM     HAIL             4 SW COZAD              40.82N 100.04W  
07/15/2008  E1.00 INCH       DAWSON             NE   LAW ENFORCEMENT   
  
1246 AM     HAIL             4 SW COZAD              40.82N 100.04W  
07/15/2008  E1.75 INCH       DAWSON             NE   LAW ENFORCEMENT   
  
0202 AM     TSTM WND GST     GRAND ISLAND            40.92N 98.37W   
07/15/2008  M61.00 MPH       HALL               NE   ASOS              
  
            GUSTS CAUSED BY HEAT BURST.  
  
0229 AM     DOWNBURST        6 WSW CHAPMAN           40.99N 98.27W   
07/15/2008                   MERRICK            NE   PUBLIC            
  
            61 MPH WINDS FROM A HEAT BURST.  
  
0310 AM     TSTM WND GST     AURORA                  40.87N 98.00W   
07/15/2008  M60.00 MPH       HAMILTON           NE   AWOS              
  
            GUST CAUSED BY HEAT BURST.  
  
0337 AM     TSTM WND DMG     CENTRAL CITY            41.11N 98.00W   
07/15/2008                   MERRICK            NE   LAW ENFORCEMENT   
  
            POWER OUTAGES AND LARGE TREE LIMBS DOWN ACROSS TOWN DUE   
            TO THUNDERSTORM WIND GUSTS.   
  
0400 AM     TSTM WND DMG     YORK                    40.87N 97.60W   
07/15/2008                   YORK               NE   LAW ENFORCEMENT   
  
            12 TO 15 INCH DIAMETER TREE LIMB WAS BLOWN DOWN.   
  
 

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