Winter Weather Forecasting Primer
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Transcript Winter Weather Forecasting Primer
Lamont Bain
OWL Director of Operations
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/
“Critical Thicknesses”
Diagnose WAA/CAA
weather.ou.edu/~metr4424
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.
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?
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
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?
SPC Sounding
BUFKIT Forecast Sounding
BUFKIT Time Series Plot
January
th
28-29
2010 Ice Storm
Saturated mid/low levels of the troposphere
Sub Freezing Temperatures at the SFC
Warm Air Aloft
Convection!?
12Z & 15Z OUN RAOBs
18Z & 21Z OUN RAOBs
0Z OUN RAOBs