An interesting weather phenomena called a "Heat Burst" happened over west central and central Minnesota during the overnight hours of Sunday July 16th to Monday July 17th. A heat burst is caused by a dying thunderstorm with very warm air aloft. The temperature at Canby jumped from 91 degrees to 100 degrees in 40 minutes (from 10:35 pm to 11:15 pm) at the same time the dew point dropped from 63 to 32 degrees. The Chanhassen National Weather Service featured a summary of the event that can be found here and also issued a Public Service Statement below.

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
242 PM CDT MON JUL 17 2006

...HEAT BURSTS AFFECTED PORTIONS OF WEST CENTRAL AND CENTRAL 
MINNESOTA LAST NIGHT...

RESIDENTS OF WEST CENTRAL AND CENTRAL MINNESOTA WERE TREATED TO AN 
UNUSUAL METEOROLOGICAL PHENOMENON LATE SUNDAY NIGHT AND EARLY MONDAY 
MORNING. DYING THUNDERSTORMS...AND A VERY WARM AND DRY LOWER AND 
MIDDLE ATMOSPHERE...LED TO THE OCCURRENCE OF SEVERAL HEAT 
BURSTS...MAINLY IN A NORTHEASTERLY SWATH FROM NEAR CANBY...IN YELLOW 
MEDICINE COUNTY...TO NEAR PAYNESVILLE IN SOUTHWESTERN STEARNS 
COUNTY. EVIDENCE OF THE BURSTS WERE DETECTED BY WEATHER OBSERVING 
EQUIPMENT AT CANBY...MONTEVIDEO...BENSON...APPLETON...WILLMAR...AND 
PAYNESVILLE.

A HEAT BURST IS CHARACTERIZED BY A DRAMATIC...ALMOST 
INSTANTANEOUS...RISE IN TEMPERATURE AND FALL IN DEW POINT 
TEMPERATURE. MOST...BUT NOT ALL HEAT BURSTS...ARE ALSO ACCOMPANIED 
BY A DROP IN SURFACE PRESSURE...LITTLE TO NO PRECIPITATION...AND 
GUSTY...RAPIDLY SHIFTING WINDS. THE MOST DRAMATIC HEAT BURSTS CAN 
EVEN CAUSE SEVERE WIND GUSTS THAT RESULT IN PROPERTY DAMAGE. 
ALTHOUGH NO DAMAGE WAS REPORTED...OBSERVING EQUIPMENT AT THE CANBY 
AIRPORT REPORTED WIND GUSTS TO 63 MPH AS A RESULT OF THE HEAT BURST.

HEAT BURSTS ARE TYPICALLY A LATE SPRING AND SUMMER...AS WELL AS A 
LATE EVENING AND NIGHTTIME PHENOMENON. THE TWO PRIMARY REASONS FOR 
THIS ARE THE ONSET OF THE NIGHTTIME INVERSION AND THUNDERSTORM 
CLIMATOLOGY. MOST HEAT BURSTS ARE ALSO DETECTED IN THE PLAINS 
STATES...BUT HEAT BURSTS HAVE ALSO BEEN RECORDED 
OVERSEAS...INCLUDING THE UNITED KINGDOM AND YEMEN.

ALTHOUGH MANY REGARD THE HEAT BURST AS A FAIRLY RARE 
PHENOMENON...HEAT BURSTS ACTUALLY OCCUR MORE OFTEN THAN MANY THINK. 
AREAS THAT HAVE A DENSE OBSERVATION NETWORK...SUCH AS THE STATE OF 
OKLAHOMA...TYPICALLY DETECT MULTIPLE HEAT BURSTS PER YEAR. IN OTHER 
AREAS OF THE PLAINS...WHERE OBSERVATION NETWORKS ARE LESS 
DENSE...HEAT BURSTS ARE DIFFICULT TO DETECT AND ARE NOT REPORTED TO 
THE NATIONAL WEATHER SERVICE UNLESS THEY RESULT IN WIND DAMAGE...OR  
HAPPEN TO AFFECT ONE OF THE FEW OBSERVING STATIONS.

SPECIFIC INFORMATION ON LAST NIGHTS HEAT BURSTS DETECTED AT EACH 
AFFECTED OBSERVING STATION ARE FOUND BELOW. THE INCREASE IN 
TEMPERATURE AND DECREASE IN DEW POINT AS A RESULT OF THE BURSTS ARE 
DENOTED IN PARENTHESES TO THE RIGHT OF THE MAXIMUM TEMPERATURE AND 
MINIMUM RECORDED DEW POINT.

LOCATION        TIME      TEMP      DEW POINT   MAX WIND GUST
-------------------------------------------------------------
CANBY           1115 PM   100 (+9)  32 (-38)    63 MPH
APPLETON        1255 AM   91 (+14)  54 (-22)    37 MPH
MONTEVIDEO      115 AM    90 (+6)   52 (-16)    23 MPH
BENSON          135 AM    97 (+15)  37 (-36)    37 MPH
WILLMAR         235 AM    97 (+18)  45 (-28)    44 MPH
PAYNESVILLE     235 AM    88 (+7)   57 (-15)    24 MPH

THIS PARTICULAR HEAT BURST OCCURRED AS DECAYING THUNDERSTORMS IN 
EASTERN SOUTH DAKOTA MOVED INTO WESTERN AND CENTRAL MINNESOTA 
SHORTLY BEFORE MIDNIGHT. RESEARCH HAS SHOWN THAT THE RADAR ECHOES 
ASSOCIATED WITH HEAT BURST ACTIVITY OFTEN TAKE ON A THIN...WAVY... 
SNAKE-LIKE APPEARANCE. THE RADAR ECHOES FROM BOTH THE CHANHASSEN 
RADAR AND THE ABERDEEN SOUTH DAKOTA RADAR HAD THIS APPEARANCE.

WITH THE UNSEASONABLY HOT TEMPERATURES THE REGION HAD EXPERIENCED 
THE PAST SEVERAL DAYS...VERY WARM...DRY...AND UNSTABLE AIR WAS IN 
PLACE OVER THE AREA. DATA FROM LAST NIGHTS WEATHER BALLOONS AT 
CHANHASSEN AND ABERDEEN SOUTH DAKOTA SHOWED THE WARM AND DRY AIR 
EXTENDED FROM THE SURFACE TO 17000 AND 20000 FEET...RESPECTIVELY. 
WHEN THE THUNDERSTORMS IN SOUTH DAKOTA AND WESTERN MINNESOTA BEGAN 
TO DECAY...A DOWNDRAFT FORMED BENEATH THEM...AND DUE TO THE UNSTABLE 
AIR IN PLACE...THE AIR ACCELERATED RAPIDLY. EVAPORATION OF RAIN 
BENEATH THE DECAYING THUNDERSTORMS ALSO FUELED THE DOWNWARD 
ACCELERATION. AS THE DOWNDRAFT APPROACHED THE SURFACE...IT WARMED 
AND DRIED...WHICH CAUSED THE DRASTIC INCREASE IN TEMPERATURE AND 
DROP IN DEW POINT. 

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URL: http://climate.umn.edu/doc/journal/heatburst070717.htm
Last modified: July 17, 2006