Long lived Thundersnow
March 23, 1966
By Kathy Lovett and Leah Smeltzer
Authors: Patrick S. Market, Rebecca L. Ebert-Cripe
Michael Bodner
March 23, 1966
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7" of snow fell in Eau
Claire, Wisconsin
North of the city
received as much as 18"
9 total hours
of thundersnow
Purpose
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To reveal characteristics of a particularly
strong long lived thundersnow event
Determine if convection was slantwise or
upright. Or whether it evolved from one type
to another.
Examine static stability and its tendency that
harbored recurrent lightning and thunder.
Methodology
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Observed data
o 82 Upper-air Radiosondes used
Special run of the Workstation Eta (WS-Eta)
mesoscale numerical weather forecasting
system developed at NCAR
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32 km convection parameterized grid spacing
captured mesoscale banding
best matched representation
Synoptic Analysis
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Synoptic ingredients for significant snow
surface low
WCB (warm isentropic conveyor belt)
500 mb vort max
300 coupled jet
Q convergence
Synoptic Analysis
Synoptic Analysis
Synoptic Analysis
Synoptic Analysis
Mesoscale analysis
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Frontogenesis
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well developed warm front
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strong ascent on warm side UVM- 20 ubs-1 over Eau Claire
Static Stability
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T advection at 700-600mb dominant
diabatic heating contributed at 700mb moister environment
Symmetric Instability
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Equivalent Potential Vorticity (EPV)-can provide access of CSI presence
SCAPE- potential of slantwise convection
Deep moisture during thundersnow
Mesoscale Analysis
Mesoscale cont.
Mg and θe contours became nearly parallel (Fig.30), suggesting an environment that was
neutral to moist slantwise perturbations
Summary
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Ws-ETA produced a successful numerical simulation
duplicating the surface cyclone, acceptable precipitation
field
cross sections revealed trend toward destabilization w/
frontogenesis, Mg, Theta E, and Omega.
 although statically stable enough, instability for
lightning was created.
Even with relatively coarse grid employed the model
rendered well the parent frontogenetic circulation and
resultant snow.
Summary
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negative EPV at 0300 UTC shows convection in the 550650 mb. Omega analysis showed sloped response. small
perturbations to 0900 UTC EPV shows conditions for
neutral moist slantwise.
Ws-Eta revealed moisture and ascent throughout most
of the event. The soundings for this event minus one
showed no CAPE. Yet showed many characteristics
expected of an thundersnow environment
Final Conclusion
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Eau Claire Thundersnow resulted from
Prolonged existence of frontogenesis
o Weak symmetric stability northeast of surface
cyclone
o Vertical Motion maximum south of the
Frontogenesis maximum
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Set-up was created and maintained by
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presence of a trowal airstream over Eau Claire for an
extended period
Features to look for to anticipate prolonged
thundersnow events
1. Presence of Trowel Axis over forecast area
a.
this was responsible to extended time period
1. Maximum in warm advection just above the
top of the temperature inversion along
trowel axis with decreasing values aloft
1. An increase in diabatic heating just above
temperature inversion along trowel axis
Features to look for to anticipate prolonged
thundersnow events
Mostly below freezing
Significant Lapse Rate
>6.5 K km-1
Frontal Inversion
Most unstable parcel
that originates from
a level warmer than -10 C
Questions?