On the afternoon of May 28, 2011, scattered thunderstorms developed across parts of the Northland, particularly northeast Minnesota. Some of these storms became severe. There were two storms in particular that were strongest. One tracked from near Brimson to near Silver Bay (pictured left, 3:11pm), and the other tracked from 4 miles south of McGrath to the Twin Ports (pictured right, 50 dBZ volume cross section at 5:34pm showing the tilt of the storm).
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Brimson to Silver Bay Storm
The image above left is a "hail swath map" from the National Severe Storms Laboratory (NSSL). This shows where an area of large hail likely fell, from just northeast of Brimson to the area north of Silver Bay. We did receive a quarter size (1-inch diameter) hail report from north of Silver Bay, but the hail was likely a bit larger to the west. The image above right is a "rotation track map" from NSSL, which essentially shows where the strongest areas of rotation were. White colors indicate the strongest rotation, then red, then yellow. This map shows how the rotation increased in the storm as it moved into southern Lake County, and then passed north of Silver Bay.
The storm mostly passed through southern portions of the Superior National Forest before crossing through Tettegouche State Park.
A NWS Storm Survey concluded that an EF-0 tornado occurred in the area approximately 16 miles west of Silver Bay, MN in the mid afternoon on May 28th. The maps of the damage are included above. The one on the left is zoomed in more on the area of the tornado, and the one on the right covers more of the entirety of the supercell thunderstorm's track across southern Lake County.
This tornado began at 3:07pm CDT approximately 7.66 miles NE of Wales, MN (47.3058, -91.6215), or just SE of Marble Lake on Forest Route 107. Some tree damage was noted along this road for almost 2 miles to the ENE. There were a few pine trees snapped or uprooted, a few ash and birch trees uprooted, and some broken birch tree limbs. The damage seemed to be focused into narrower corridors within the broader tornado path, possibly indicative of smaller vorticies within the overall tornado. This matches well with an eyewitness report that we received around 3:13pm during the event. The person reported a rotating wall cloud with some small funnels occasionally dipping out. The tornado ended at 3:10pm CDT approximately 8.80 miles S of Whyte, MN (47.3242, -91.5880).
Peak winds were estimated at 70-80mph, within the EF-0 range on the Enhanced Fujita Scale. This was the first recorded tornado in Lake County, Minnesota since September 16, 1992.
Below is a small sample of the tree damage. Some of the tree damage was mixed in with dense forest, which made it difficult to photograph. You'll also notice some tree debris near the side of the road where some cleanup had already taken place.
Sporadic tree damage was noted along the path of the supercell thunderstorm from near where it crossed Lake County Highway 2 eastward to the western border of Tettegouche State Park and the Lax Lake area. None of this damage was convergent or concentrated enough to be considered tornadic, and thus was likely due to occasional downbursts during the thunderstorm life cycle, with wind gusts up around 65 mph.
McGrath to Duluth Storm
To the right is another hail swath map from NSSL showing approximately where hail fell with the storm that moved from McGrath all the way into Superior and Duluth. The algorithm that produces this map indicated that the largest hail that fell out of this storm probably fell in far southeast Aitkin County and into the Moose Lake area of far southern Carlton County.
We did receive a quarter size hail report from near Sturgeon Lake in far northern Pine County, at mile marker 212 on Interstate 35. There were also numerous reports of dime to quarter size hail in Carlton County, and then numerous reports of pea size hail in Duluth.
Here is a summary of other reports that we received from the storms on May 28th:
PRELIMINARY LOCAL STORM REPORT...SUMMARY NATIONAL WEATHER SERVICE DULUTH MN 1052 AM CDT SUN MAY 29 2011 ..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON... ..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE.... ..REMARKS.. 0230 PM TSTM WND DMG 6 S TOWER 47.72N 92.29W 05/28/2011 ST. LOUIS MN LAW ENFORCEMENT CORRECTED TIME. TREE BLOWN DOWN BLOCKING HIGHWAY 135 NEAR HIGHWAY 26. LAKE COUNTY SHERIFFS OFFICE. 0245 PM HAIL 14 W ISABELLA 47.62N 91.66W 05/28/2011 E0.75 INCH LAKE MN TRAINED SPOTTER SOME GUSTY WINDS ACCOMPANIED THE HAIL. 0258 PM TSTM WND DMG 5 ESE ELY 47.88N 91.75W 05/28/2011 LAKE MN PUBLIC A COUPLE TREES BLOWN DOWN ALONG THE KAWISHIWI TRAIL 0304 PM TSTM WND DMG 7 NE WALES 47.30N 91.64W 05/28/2011 LAKE MN NWS STORM SURVEY SOME TREES AND TREE LIMBS BLOWN DOWN IN AN AREA BETWEEN MARBLE LAKE AND KANE LAKE. LIKELY ASSOCIATED WITH A DOWNBURST BEFORE A TORNADO FORMED JUST EAST. 0307 PM TORNADO 8 NE WALES 47.31N 91.62W 05/28/2011 F0 LAKE MN NWS STORM SURVEY TREE DAMAGE WAS NOTED ALONG A 1.9 MILE LONG PATH IN THE SUPERIOR NATIONAL FOREST ALONG FOREST ROUTE 107. THIS CONSISTED OF A FEW SNAPPED AND UPROOTED TREES...ALONG WITH BROKEN TREE LIMBS. PATH WIDTH 350 YARDS. LASTED APPROX 3 MINUTES. RATED AN EF-0 ON ENHANCED FUJITA SCALE WITH EST PEAK WINDS 70 TO 80 MPH. 0311 PM TSTM WND GST HIBBING 47.40N 92.95W 05/28/2011 M47.00 MPH ST. LOUIS MN ASOS 47 MPH WIND GUST REPORTED AT THE HIBBING ASOS AT 311 PM. 0320 PM TSTM WND DMG 7 WNW SILVER BAY 47.33N 91.43W 05/28/2011 LAKE MN NWS STORM SURVEY SOME SPORADIC MINOR TREE DAMAGE ALONG HIGHWAY 15. SOME BROKEN TREE LIMBS AND A FEW TREES BLOWN DOWN. 0325 PM FUNNEL CLOUD 5 W SILVER BAY 47.29N 91.39W 05/28/2011 LAKE MN TRAINED SPOTTER ROTATING WALL CLOUD WITH BRIEF FUNNELS OR VORTICIES DIPPING OUT OF THE BASE OF THE CLOUD. NO CONTACT WITH THE GROUND HAS BEEN OBSERVED. 0328 PM TSTM WND DMG 4 NNW SILVER BAY 47.34N 91.32W 05/28/2011 LAKE MN NWS STORM SURVEY SOME TREE LIMBS BROKEN OFF NEAR LAX LAKE. 0328 PM HAIL 5 N SILVER BAY 47.36N 91.28W 05/28/2011 E1.00 INCH LAKE MN TRAINED SPOTTER 0332 PM FUNNEL CLOUD 4 N SILVER BAY 47.35N 91.29W 05/28/2011 LAKE MN PARK/FOREST SRVC LOW HANGING...ROTATING FUNNEL / CLOUDS OBSERVED PASSING OVER LAX LAKE ON WEST SIDE OF TETTEGOUCHE STATE PARK. TIME IS ESTIMATED. 0335 PM FUNNEL CLOUD 3 N SILVER BAY 47.34N 91.28W 05/28/2011 LAKE MN TRAINED SPOTTER FUNNEL CLOSER TO THE GROUND. FROM PREVIOUS REPORT 10 MINUTES AGO. 0335 PM TSTM WND DMG GILBERT 47.49N 92.46W 05/28/2011 ST. LOUIS MN LAW ENFORCEMENT TREE DOWN IN GILBERT. LAKE COUNTY SHERIFFS OFFICE. 0340 PM HAIL 1 W ILLGEN CITY 47.35N 91.20W 05/28/2011 E0.75 INCH LAKE MN PARK/FOREST SRVC SOME GUSTY WINDS AND HEAVY RAIN WITH THE HAIL. 0345 PM FUNNEL CLOUD 2 ESE ILLGEN CITY 47.34N 91.15W 05/28/2011 LSZ142 MN PARK/FOREST SRVC LOW HANGING...ROTATING FUNNEL / CLOUDS OBSERVED OVER LAKE SUPERIOR FROM NEAR THE MOUTH OF THE BAPTISM RIVER. 0350 PM TSTM WND DMG 2 N SIDE LAKE 47.69N 93.02W 05/28/2011 ST. LOUIS MN LAW ENFORCEMENT THREE TREES DOWN BLOCKING HIGHWAY 5 AND PERCH LAKE ROAD. LAKE COUNTY SHERIFFS OFFICE. 0450 PM HAIL 1 W ILLGEN CITY 47.35N 91.20W 05/28/2011 E0.88 INCH LAKE MN PARK/FOREST SRVC JUST UNDER QUARTER SIZE. 0530 PM HAIL 4 S STONE LAKE 45.79N 91.54W 05/28/2011 E0.50 INCH WASHBURN WI TRAINED SPOTTER DIME SIZE HAIL 0538 PM HAIL 2 ENE STURGEON LAKE 46.39N 92.72W 05/28/2011 E1.00 INCH PINE MN TRAINED SPOTTER CORRECTED TIME AND SPECIFIC LOCATION. REPORTED AT MILE MARKER 212 ON I-35. 0545 PM HAIL 3 ESE MOOSE LAKE 46.43N 92.71W 05/28/2011 E1.00 INCH CARLTON MN PARK/FOREST SRVC 0.5 TO 1.0 INCH DIAMETER HAIL. BIGGEST HAIL STONES WERE AROUND THE SIZE OF A QUARTER. SOME GUSTY WINDS. AT MOOSE LAKE STATE PARK. 0545 PM HAIL 1 SE MOOSE LAKE 46.44N 92.75W 05/28/2011 E0.88 INCH CARLTON MN TRAINED SPOTTER 0608 PM HAIL 1 W WRENSHALL 46.62N 92.40W 05/28/2011 E0.75 INCH CARLTON MN TRAINED SPOTTER MARBLE TO DIME SIZE HAIL. 0612 PM HAIL CARLTON 46.66N 92.42W 05/28/2011 E0.75 INCH CARLTON MN AMATEUR RADIO 0615 PM HAIL NEW DULUTH 46.68N 92.21W 05/28/2011 E0.50 INCH ST. LOUIS MN TRAINED SPOTTER ALSO SOME GUSTY WINDS WITH A SWING SET AND SOME SMALL TREE BRANCHES BLOWN DOWN. 0619 PM HAIL GARY NEW DULUTH 46.68N 92.21W 05/28/2011 E0.75 INCH ST. LOUIS MN AMATEUR RADIO