1. PECAN CSWR interest IOP 15 24/25 July 2015 MCS in W Illinois

2. Overview Map * Dows are blue disks * Dual lobes are 30 o min crossing: Green Blue: D8-D7 Dark Blue: D7-D6 * Light green polygons are where CI occurred and moved ENE. * Low-level blockage is shown as grey sectors for each radar. Large areas are blockage by cab. * Gust front shown at three times as kink develops vortex (circles along red line near Stronghurst). * Loss of features in east part due to attenuation. D6 D7 D8

3. DOW views of Gust Front approaching Simultaneous view of gust front (DBM top, VEL bottom) for each radar at about the same time at elevation 1 o. All are centered at about the same geographic location. Some CI is also evident NW of D7 (NE of D6) and SE of D7 (SW of D8). DOW-6 DOW-8 DOW-7

4. Gust Front as kink develops DOW-6 DOW-8 DOW-7 Simultaneous view of gust front (DBM top, VEL bottom) for each radar at about the same time at elevation 1 o. All are centered at about the same geographic location. Dow6 miss- placed beam issue shown.

5. Dual potential as vortex forms DOW-6 DOW-7 DOW-8

6. Vortex in best form – Dow-7 05:43:53 Elv = 1.0 deg. Z = 170 m. Note color table centered at -5.0 m/s. Small inner vortex (circle) with RFD-like structure just W of gust front. Speed maxes inner vortex are -27/+23 m/s and in “RFD” -36 m/s. Inset: 0.5 deg (Z=80 m) 9 s earlier showing max winds of -28 & +25 m/s. Same spatial and color scales. 5 km

7. Nearby CI – Dow-8 Just before CI 05:0505:10 05:15 05:33 05:43 Wind ripples become evident. Maturing cell with larger disturbance in wind field. More CI to SW. Mini gust front forming. Wind field resembles pebbles dropped into pond, with concentric waves.

8. IOP15 good points 1.Gust front with evolving kink 2.Fairly strong, well formed vortex on kink with possibility of some dual 3.CI events, including very near radars, possibly dual IOP15 bad points 1.Attenuation hurt dual obs, and obscured vortex to all radars at certain times.