1. Kevin Birk, Mike Bardou and Mark Ratzer WFO Chicago

2. Review of Two Storm Force Wind Events across Lake MI 1. October 26 th “Bomb” 2. December 12 th Winter Storm  Both events produced Storm force winds (48+ knots).  However, the strength and the tracks of the two lows were quite different.

3. Motivation  Increase the forecast accuracy for the onset of high impact winds across Lake Michigan. -> Gain a better understanding of the main processes that govern the onset and maintenance of storm force winds across the lake.

4.  Central pressure dropped from 980 mb at 00UTC on the 26 th to 955 mb at 00UTC on the 27 th as the surface low tracked across MN.  Lake MI remained in the warm sector through the morning of the 26 th.  Occluded front pushed across the lake late morning on the 26 th.  Following this, the system filled as the low became vertically stacked. The October 26 th Bomb

5. 12 UTC Oct 26 th 00 UTC Oct 27 th 300 MB Jet and Surface

6. 12 UTC Oct 27 th 00 UTC Oct 28 th 300 MB Jet and Surface

7. 12 UTC October 26 th

8. 15 UTC October 26 th

9. 18 UTC October 26 th

10. 21 UTC October 26 th

11. 00 UTC October 27 th Adiabatic Lapse Rate

12. Forecasts For Oct 26 th Event  Headlines for Gale/Storm watch first issued at 3:42 AM Sun 10/24  Gale watch from Monday PM – Tuesday AM.  Storm watch from Tuesday PM – Wed evening.  Headlines upgraded to Storm Warning at 4:01 AM Mon 10/25.  Warning from 4 AM Tue -7 PM Wed.  Later forecasts shifted times slightly.

13. North Half Verification  Winds remained below Gale force Until about 10 AM Tue 26 th as the cold front passed.  Gusts remained below Storm force at the north buoy (peaked at 47 knots Tue PM).  Port Inland, MI peaked at 56 knots Wed AM. Frontal Passage

14. South Half Verification  Winds remained below Gale force Until about 7 AM Tue 26 th as the cold front passed.  Gusts remained below Storm force at the south buoy (peaked at 45 knots Tue PM).  Chicago Harrison Crib peaked at 65 knots Tues AM. Frontal Passage

15. December 12 th Winter Storm  Surface Low tracked across Northern IL/Southern Lake MI during predawn hours on the 12 th.  The low deepened to 988 mb during the afternoon on the 12 th as the low moved across western New York.  Farther Northwest, Canadian high pressure of 1038 mb moved across eastern Dakotas.

16. 12 UTC Dec 12 th 300 MB Jet and Surface 00 UTC Dec 13 th

17. 12 UTC December 12 th

18. 15 UTC December 12 th

19. 21 UTC December 12 th

20. 03 UTC December 13 th

21. Super Adiabatic Lapse Rate

22. Forecasts For Dec 12 th Event  Headlines for Gale/Storm watch first issued at 8:50 AM December 10 th.  Late Saturday the 11 th through Monday morning the 13 th.  Winds to 55 knots on Sunday/Sunday Night the 12 th.  Headlines upgraded to Storm Warning at 2:27 PM on the 11 th.  Late Saturday the 11 th through Monday morning the 13 th.  Winds to 55 knots on Sunday/Sunday Night the 12 th.

23. Verification North Half  Winds increased to Gales around 04 UTC and to Storm by 10 UTC.  Storm force winds ended around 11 UTC on the 13 th (25 hours of storm). South Half  Winds increased to Gales/Storm around 14 UTC.  Storm force winds ended around 05 UTC on the 13 th (15 hours of storm).

24. Considerations  Stability over the lake  Boundary layer lapse rates.  Near adiabatic -> gusts = boundary layer winds.  Super adiabatic -> gusts = the max wind in the boundary layer.  The track of the low and time of year.  Strength of cold air advection.  Dynamics  Isallobaric wind component.  Synoptic scale descent following the passage of a mid level vorticity max and dry slot.

25. Questions?