1. Lamont Bain OWL Director of Operations

2. Thickness Thickness- distance between two pressure surfaces, usually denoted in decameters. Derived using the hypsometric equation: Knowing the thickness between two different pressure surfaces can give you an idea of the mean temperature in that layer. Diagnose Warm Air Advection (WAA) and Cold Air Advection (CAA) at the surface using “the trapezoid” method and diagnose possible boundaries. Suggested reading: www.theweatherprediction.com/winterwx/thicknesscrit eria/

3. “Critical Thicknesses”

4. Diagnose WAA/CAA weather.ou.edu/~metr4424

5. Thickness Sources HOOT: 1000-500 mb thickness with 500mb heights and temperatures (expansion is anticipated) Patrick Marsh’s Map: Page 1000-500mb thickness with MSLP College of Dupage: Various Layers for Critical Thickness.

6. Forecast Soundings: A top-down approach Not just for thunderstorms! Guide for thermal structure and thus “p-type.” Ice Nucleation and Snow Growth Freezing Rain? Sleet? Snow? Just a cold rain?

7. Ice Crystals For Snow to occur, ICE MUST BE PRESENT IN CLOUD Plains -9C suggests that IN have become activated. -15C ice is likely! -12C to -16C layer is often refereed to as the Dendridic Growth Zone or DGZ (per RAOBs) How do I determine the temperature? – RAOB or IR Satellite Imagery

8. Top-Down Method Is it cold enough to support ice crystals in clouds? Are UVVs and higher RH values (or other moisture proxy) collocated within the Dendritic Growth Zone? Negative Omega-Upward Vertical Motion Positive Omega-Downward Vertical Motion Is there any WAA/CAA in the column? Dry or Moist Advection at mid/upper levels? Evaporative Cooling/Melting? Will temperatures at the surface support liquid, freezing, or frozen precipitation?

9. SPC Sounding

10. BUFKIT Forecast Sounding

11. BUFKIT Time Series Plot

12. January 28-29 th 2010 Ice Storm Saturated mid/low levels of the troposphere Sub Freezing Temperatures at the SFC Warm Air Aloft Convection!?

13. 12Z & 15Z OUN RAOBs

14. 18Z & 21Z OUN RAOBs

15. 0Z OUN RAOBs