An area of surface low pressure tracked from near Cooperstown (ND) in the early afternoon to near Detroit Lakes (MN) by early evening. Abundant sunshine along and south of this line contributed to a healthy amount of instability through the afternoon into the evening.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS FGF wrote it up.
An area of surface low pressure tracked from near Cooperstown (ND) in the early afternoon to near Detroit Lakes (MN) by early evening. Abundant sunshine along and south of this line contributed to a healthy amount of instability through the afternoon into the evening. Thunderstorms flared up by mid afternoon in the New Rockford (ND) area and tracked southeast to near Fergus Falls (MN) by early evening, producing some large hail, damaging winds, and heavy amounts of rain.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Grand Forks, ND wrote its last area forecast discussion before the first event at Aug 12, 8:13 AM CST, 4 hours 12 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAND FORKS ND 913 AM CDT FRI AUG 12 2011 .DISCUSSION...MORNING UPDATE FOCUSES ON FINE TUNING POPS AND WEATHER GRIDS. A WEAK CONVERGENT BOUNDARY CONTINUES ALONG A LINE FROM TWIN VALLEY TO LAKE ITASCA. THERE IS SOME VERY WEAK SFC CONVERGENCE SOUTH OF THE LINE...WHILE THE H850 FLOW SHOWS WEAK CONVERGENCE NORTH OF THIS LINE. THE H850 CONVERGENCE BECOMES MORE EVIDENT THIS AFTERNOON WITH NOT A WHOLE LOT OF EASTWARD MOVEMENT. THUS WILL UPDATE TO LIKELIES THROUGH 00Z. UPPER LOW CONTINUES TO EDGE ITSELF INTO WRN NORTH DAKOTA...AND RIGHT NOW THE ECMWF SEEMS TO HAVE THE BEST HANDLE ON ITS LOCATION AS THE GFS/NAM SHOW AN OPEN WAVE (NAM IN LATER PDS...NOT CURRENT). WE ARE STARTING TO SEE TSTM DEVELOPMENT OVER THE SO URIS RIVER BASIN IN WEST CENTRAL NORTH DAKOTA...SO WILL LIKELY BUMP UP POPS IN THE DVL LAKE BASIN FOR 15Z TO 18Z TIMEFRAME. TEMP GRIDS LOOK DECENT AT THE CURRENT TIME AND ANTICIPATE NO CHANGES TO TO DAYS HIGHS. && .AVIATION...MAJORITY OF THE PERIOD WILL BE VFR. MAIN CONCERN WILL BE THUNDER CHANCES...ALTHOUGH CONFIDENCE IN EXACT TIMING AND LOCATION IS LOW. THINK MOST TAF SITES WILL EXPERIENCE SOMETHING AT SOMETIME TODAY OR THIS EVENING...AND WILL TRY TO FORECAST BEST TIMING. && .PREV DISCUSSION... /ISSUED 358 AM CDT FRI AUG 12 2011/ SHORT TERM...CONCERNS WILL REVOLVE AROUND TODAY WITH REGARDS TO THUNDER CHANCES...SEVERE POTENTIAL...AND LOCALLY HEAVY RAIN POTENTIAL. 00Z MODELS INITIALIZED WITH MINIMAL ERRORS. NAM/ECMWF/SREF/GEM HAVE TRENDED SLOWER WITH MAIN 500MB LOW. GFS IS ON THE FAST SIDE OF MODEL CONSENSUS. THIS 500MB LOW APPEARS RATHER STRONG ON WATER VAPOR IMAGERY...SO A SLOWER SOLUTION MAKES THE MOST SENSE. TRENDED THE FORECAST IN THIS DIRECTION. SCATTERED THUNDERSTORMS WILL BE POSSIBLE THROUGH THE MORNING HOURS WITH MANY BOUNDARIES AND WEAK SHORTWAVES IN PLACE AHEAD OF THE MAIN SYSTEM. THERE WILL LIKELY BE AN AREA OF MORE WIDESPREAD SHOWERS AND THUNDERSTORMS THIS AFTERNOON INTO THE EVENING HOURS AS THE MAIN SYSTEM PASSES THROUGH. MODEL CONSENSUS PLACES THE UPPER LOW NEAR JAMESTOWN AT 00Z SAT...AND NEAR THE SOUTHEAST FA BY 06Z SAT. THIS PLACES AREAS ALONG AND SOUTH OF A DVL-GFK-BJI LINE IN A FAVORED LOCATION FOR PRECIP...AND INCREASED POPS TO LIKELY FOR THIS AFTERNOON INTO THE EVENING HERE. BEST SEVERE POTENTIAL WILL BE ACROSS THE FAR SOUTHERN FA...WHERE INSTABILITY AND DEEP LAYER SHEAR WILL BE STRONGEST. DEEP LAYER SHEAR ACROSS MUCH OF THE FA WILL BE AOB 15 KNTS...WHICH SHOULD PREVENT SEVERE POTENTIAL (HOWEVER...BRIEF ISOLD SEVERE POSSIBLE). DEEP LAYER SHEAR ACROSS THE FAR SOUTHERN FA WILL BE 20-30KNTS. ALTHOUGH NOT STRONG...MID-LEVEL TEMPS WILL BE COOLING...AND MLCAPE VALUES UP TO 2000 J/KG POSSIBLE. THIS COMBINED WITH WEAK SFC LOW IN THE VICINITY...AND DYNAMICS COULD PROVIDE LONGER DURATION SEVERE STORMS. SPC DOES HAVE THIS AREA IN A SLIGHT RISK. STORM MOTION WILL BE VERY SLOW (LESS THAN 10 KNTS)...WHICH RAISES CONCERNS FOR LOCALLY HEAVY RAINFALL. HIGH RESOLUTION MODELS SIGNALING THE POTENTIAL FOR ISOLATED AREAS RECEIVING 2-4 INCHES ACROSS SE NORTH DAKOTA AND ADJACENT PORTIONS OF MINNESOTA. YESTERDAY...A COUPLE LOCATIONS REPORTED UP TO 5 INCHES OF RAINFALL. WILL MENTION LOCALLY HEAVY RAINFALL ACROSS SOUTHEAST ND AND ADJACENT PORTIONS OF MINNESOTA...WHERE THE BEST POTENTIAL FOR HEAVIER RAINFALL EXISTS. EXPECT MOST LOCATIONS TO RECEIVE AROUND 0.50 INCH OF RAINFALL. AT THIS TIME THINK THAT HEAVIER RAINFALL WILL BE RATHER ISOLD...AND NO PLANS OF A FLASH FLOOD WATCH...BUT WILL NEED TO MONITOR. SAT-SUN...WITH MODELS TRENDING SLOWER...CLOUDS MAY LINGER INTO SATURDAY. OTHERWISE...RIDGING WILL BUILD INTO THE REGION...AND EXPECT DRY WEATHER AND NEAR NORMAL TEMPERATURES. LONG TERM...MODELS GENERALLY AGREE WITH THE FORECAST AND NO CHANGES PLANNED. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...NONE. MN...NONE. && SPEICHER
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE GRAND FORKS ND 435 AM CDT FRI AUG 12 2011 MNZ001>009-013>017-022>024-027>032-040-NDZ006>008-014>016-024- 026>030-038-039-049-052>054-131200- WEST POLK-NORMAN-CLAY-KITTSON-ROSEAU-LAKE OF THE WOODS- WEST MARSHALL-EAST MARSHALL-NORTH BELTRAMI-PENNINGTON-RED LAKE- EAST POLK-NORTH CLEARWATER-SOUTH BELTRAMI-MAHNOMEN- SOUTH CLEARWATER-HUBBARD-WEST BECKER-EAST BECKER-WILKIN- WEST OTTER TAIL-EAST OTTER TAIL-WADENA-GRANT-TOWNER-CAVALIER- PEMBINA-BENSON-RAMSEY-EASTERN WALSH-EDDY-NELSON-GRAND FORKS- GRIGGS-STEELE-TRAILL-BARNES-CASS-RANSOM-SARGENT-RICHLAND- WESTERN WALSH- 435 AM CDT FRI AUG 12 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EASTERN NORTH DAKOTA...WEST CENTRAL AND NORTHWEST MINNESOTA. .DAY ONE...TODAY AND TONIGHT SHOWERS AND THUNDERSTORMS WILL OCCUR TODAY. LOCALLY HEAVY RAINFALL IS POSSIBLE...ESPECIALLY ACROSS SOUTHEASTERN NORTH DAKOTA AND ADJACENT PORTIONS OF MINNESOTA. ISOLATED AREAS COULD RECEIVE 2 INCHES OR MORE IN A SHORT DURATION. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS NEAR THE SOUTH DAKOTA BORDER INTO ADJACENT PORTIONS OF MINNESOTA THIS AFTERNOON AND EVENING. LARGE HAIL...STRONG WINDS...AND A TORNADO ARE POSSIBLE. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY THERE WILL BE MULTIPLE CHANCES FOR THUNDERSTORMS NEXT WEEK. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS POSSIBLE TODAY. IF HEAVY RAIN DOES OCCUR AT YOUR LOCATION...PLEASE REPORT. TG
PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE EASTERN ND/GRAND FORKS ND
945 AM CDT FRI AUG 12 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0308 PM HAIL 2 SW HILLSBORO 47.38N 97.09W
08/11/2011 E0.75 INCH TRAILL ND PUBLIC
PEA TO DIME SIZED HAIL.
0320 PM HEAVY RAIN 3 SSE HILLSBORO 47.36N 97.04W
08/11/2011 M1.07 INCH TRAILL ND BROADCAST MEDIA
BRIEF BUT VERY HEAVY RAIN MIXED WITH STRONG WINDS AND
HAIL BROUGHT ALL LANES OF TRAFFIC TO A STOP ALONG
INTERSTATE 29 NEAR MILEPOST 100. TRAFFIC WAS ABLE TO
RESUME AFTER ABOUT A 10 TO 15 MINUTE PERIOD. HEAVY RAIN
FELL OVER A ROUGHLY 20 MINUTE PERIOD. A NEARBY NDAWN
MESONET SITE MEASURED PEAK WINDS TO 48 MPH AND 1.07
INCHES OF RAIN DURING THE PERIOD.
0350 PM HAIL 2 SW ERSKINE 47.64N 96.04W
08/11/2011 E1.25 INCH POLK MN PUBLIC
QUARTER TO WALNUT SIZED HAIL FOR A FEW MINUTES.
0405 PM HAIL 3 ESE ERSKINE 47.65N 95.95W
08/11/2011 E0.75 INCH POLK MN PUBLIC
0525 PM HAIL GRAND FORKS 47.92N 97.07W
08/11/2011 M0.88 INCH GRAND FORKS ND NWS EMPLOYEE
PEA TO NICKEL SIZED HAIL ON THE SOUTH SIDE OF GRAND
FORKS. LASTED UNTIL 529 PM.
0530 PM HEAVY RAIN 6 SE COOPERSTOWN 47.38N 98.03W
08/11/2011 E5.00 INCH GRIGGS ND CO-OP OBSERVER
TIME APPROXIMATE. TOTAL RAINFALL OVER A ROUGHLY 3 HOUR
PERIOD.
0537 PM HAIL GRAND FORKS 47.92N 97.07W
08/11/2011 M1.25 INCH GRAND FORKS ND PUBLIC
QUARTER TO HALF DOLLAR SIZED HAIL FELL.
0545 PM TSTM WND DMG GRAND FORKS 47.92N 97.07W
08/11/2011 GRAND FORKS ND PUBLIC
12-INCH DIAMETER TREE SNAPPED AT ROOT AT CORNER OF 28TH
AVE AND OAK STREET. TIME APPROXIMATE.
&&
GGUSTThe national radar mosaic for the moment the first event began.
6 hail, 3 heavy rain, 1 thunderstorm wind. Local standard time, as filed.
Torrential rains fell along with numerous nickel to walnut sized hail. The hail began small but increased in size later on.
The observer also measured 3.30 inches of rain during the storm.
Nickel to quarter sized hail caused some crop damage.
A few walnut sized hail fell.
The observer reported 2.75 inches of rain.
The observer reported 1.82 inches of rain over a two hour period.
The winds were measured at Hector Airport on the north end of Fargo.
About 3.50 inches of rain fell over the course of about 45 minutes.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in North Dakota in 2011Every state in 2011This day in weather historyWarnings in North Dakota, August 2011
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 326946, 326947, 326948, 326949, 326950, 326953, 326956, 326971, 326954, 326962.