Long lived Thundersnow March

23, 1966By Kathy Lovett and Leah Smeltzer

Authors: Patrick S. Market, Rebecca L. Ebert-Cripe

Michael Bodner

March 23, 1966• 7" of snow fell in

Eau Claire, Wisconsin

• North of the city received as much as 18"

• 9 total hours of thundersnow

Purpose• 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• Observed data

o 82 Upper-air Radiosondes used

• Special run of the Workstation Eta (WS-Eta) mesoscale numerical weather forecasting system developed at NCARo 32 km convection parameterized grid spacing o captured mesoscale bandingo best matched representation

Synoptic Analysis• Synoptic ingredients for significant

snowsurface lowWCB (warm isentropic conveyor belt)500 mb vort max300 coupled jetQ convergence

Synoptic Analysis

Synoptic Analysis

Synoptic Analysis

Synoptic Analysis

Mesoscale analysis• Frontogenesis

o well developed warm fronto strong ascent on warm side UVM- 20 ubs-1 over Eau Claire

• Static Stability o T advection at 700-600mb dominanto diabatic heating contributed at 700mb moister environment

• Symmetric Instability o Equivalent Potential Vorticity (EPV)-can provide access of CSI

presenceo SCAPE- potential of slantwise convectiono 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• 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• negative EPV at 0300 UTC shows convection in

the 550-650 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• Eau Claire Thundersnow resulted from

o Prolonged existence of frontogenesiso Weak symmetric stability northeast of surface

cycloneo Vertical Motion maximum south of the

Frontogenesis maximum

• Set-up was created and maintained byo 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 areaa. this was responsible to extended time period

2.Maximum in warm advection just above the top of the temperature inversion along trowel axis with decreasing values aloft

3.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 parcelthat originates from a level warmer than -10 C

Questions?