Strong to severe thunderstorms affected western and central Upper Michigan during the afternoon and evening hours of May 20th, 2012. Low-level moisture and abundant sunshine ahead of an approaching cold front allowed for moderately unstable air to develop across Upper Michigan. Many of these storms were small and short-lived, but produced some large hail, gusty winds, and very heavy rainfall. The first loop below is of the radar from early afternoon to early evening. The cold front induced storms in a somewhat linear fashion.
One of the advantages of the recent dual-polarization radar upgrade was noticed this afternoon on many of the storms. Within the oval on the upper left and lower right images below, a feature called a "three-body scatter spike" is apparent. This feature occurs when large hail inside a storm sends the radar beam to the ground, back to the storm, then back to the radar (hence, "three" bodies). Though this has been visible with multiple radar products in the past, the inclusion of correlation coefficient (how similar the objects are within a storm, for example) with the recent upgrade increases confidence that there is indeed hail in the storm. The very low values (blue) are a big indicator of a three-body scatter spike (lower right image).
Within the rectangle, we notice that the upper right image, ZDR, has a lower value than surrounding locations. ZDR measures the shape of the objects, with flat objects, like large rain drops, producing high positive values. On the other hand, spherical objects, like hail, result in values closer to zero, as seen here. Thus, confidence is once again increased with regards to whether or not hail is located within this storm.
The second loop below is of the visible satellite from mid morning to early afternoon. Notice how cumulus clouds (small pockets of white) developed across central Upper Michigan during the afternoon. Also notice that there is a lack of cumulus clouds in the east. South winds off of the cool waters of Lake Michigan prevented the air from becoming as unstable as further west, thus inhibiting clouds. The boundary of this air, seen as a denser white line across eastern Marquette county, kicked off a few thunderstorms in the afternoon ahead of the main line of storms to the west.
Below is a summary of reports. In addition, we had numerous reports of pea sized hail with many of the storms, including here at the NWS office near Negaunee.
Time Event-Magnitude City, County
1233 PM Hail-0.50 Inch Rockland, Ontonagon
0117 PM Hail-1.00 Inch 2 E Redridge, Houghton
0130 PM Hail-0.75 Inch 3 ENE HoughtonHoughton
0130 PM Hail-0.88 Inch 2 E HoughtonHoughton
0132 PM Hail-0.50 Inch Marquette,Marquette
0134 PM Hail-0.50 Inch 3 NE Houghton,Houghton
0139 PM Hail-0.88 Inch Ironwood,Gogebic
0145 PM Hail-1.00 Inch Calumet,Houghton
0357 PM Hail-0.75 Inch 4 S Mass City,Ontonagon
Wind gusts up to 40mph as well.
0410 PM Hail-0.75 Inch 5 ESE Chassell, Houghton
0440 PM Hail-0.50 Inch Houghton,Houghton
0450 PM Hail-0.50 Inch L`Anse,Baraga
0530 PM Tstm Wnd Dmg 6 S Witch Lake, Dickinson
24 Inch White Pine tree knocked over. Estimated winds of 60mph.
0534 PM Tstm Wnd Dmg 2 SSE Witch Lake, Marquette
Trees down across highway M-95 along the Marquette/Dickinson
0546 PM Tstm Wnd Dmg 5 WNW Big Bass Lake, Marquette
Small limbs down. Patio furniture blown across the yard.
Very strong winds, no estimate.
0600 PM Hail-0.50 Inch 2 W Ishpeming, Marquette
0604 PM Hail-0.75 Inch Kingsford, Dickinson
0606 PM Hail-0.75 Inch 1 S Granite Bluff, Dickinson
0635 PM Hail-0.50 Inch 2 SSE Norway, Dickinson
0707 PM Hail-0.75 Inch 4 NE Gwinn, Marquette
0721 PM Hail-0.75 Inch 1 SW Shot Point, Marquette
0832 PM Heavy Rain-1.75 Inch 10 E Ontonagon,Ontonagon
Total rainfall since noon. Small creek on residence is
over its banks.