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Winter Weather Forecasting Primer

Discover essential winter weather forecasting methods with this primer by Lamont Bain, OWL Director of Operations. Learn about the significance of thickness—measuring the distance between pressure surfaces—and how it relates to mean temperatures in weather layers. Explore techniques for diagnosing Warm Air Advection (WAA) and Cold Air Advection (CAA) using the trapezoid method. This guide includes key information on ice nucleation, snow growth, and critical thickness criteria, making it invaluable for meteorologists and weather enthusiasts alike.

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Winter Weather Forecasting Primer

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  1. Winter Weather Forecasting Primer 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/thicknesscriteria/

  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 28-29th 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

  16. Questions? Concerns? Comments?

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