A “Survey” of Tornadoes A “Survey” of Tornadoes and their Environments and their Environments

in the in the

WFO Sterling, VA WFO Sterling, VA Forecast AreaForecast Area

Matthew R. KramarMatthew R. KramarSenior Forecaster, WFO LWXSenior Forecaster, WFO LWX

Kyle M. OlmsteadKyle M. OlmsteadStudent Volunteer, WFO LWXStudent Volunteer, WFO LWX

Motivation

• Provide guidance to forecasters on favorable synoptic patterns for tornadoes in the WFO LWX forecast area

• Update local graphics to reflect recent geographical and temporal distribution of tornadoes by tornadic storm type

Methodology

• Compiled dataset of tornado events from 1992-2009 (WSR-88D era at WFO LWX)

• Stratified reports by storm mode based on inspection of Level II data

Methodology

• Stratification of tornadoes by storm mode:– Mesocyclonic– Linear/Quasi-Linear Convective System

• Sub-stratified into linear and QLCS based on QLCS definition by Coniglio et al. (2007)

– Other• Disorganized, non-mesocyclonic cells,

waterspout/landspout type tornado – Tropical/Tropical remnant system– No Level II data available

Methodology

• Stratification of tornadoes by storm mode:– Considered only mesocyclonic and linear/QLCS

tornadoes• Unusual juxtaposition of shear/instability in remnant

tropical environments• Potentially important role of sub-synoptic conditions in

landspout/waterspout tornado development

Distribution by Month (1992-2009)Number of Days with Tornado Reports by Month

0

5

10

15

20

25

30

Jan

uar

y

Feb

ruar

y

Mar

ch

Ap

ril

May

Jun

e

July

Au

gu

st

Sep

tem

ber

Oct

ob

er

No

vem

ber

Dec

emb

er

Month

Nu

mb

er o

f D

ays

All Types

Distribution by Month (1992-2009)

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Number of Days of Tornado Occurrence (1992-2009)

0 1 2 3 4 5 6

Number of Days of Mesocyclonic Tornado Occurrence

0 1 2 3 4 5 6

Number of Days of Linear/QLCS Tornado Occurrence

Methodology

• Constructed synoptic composites based upon tornadic storm mode– NCEP/NCAR Reanalysis

• 2.5° x 2.5° lat/lon grid• 6-hourly data• Lose mesoscale details• Seasonal impact on thermodynamic aspects?

– Chose 6-hour synoptic time closest to and preceding tornado event

Compositing• Variables

– Geopotential Height– Zonal Wind– Meridional Wind– Vector Wind– Sea Level Pressure– Relative Humidity– Temperature

• Height Levels (mb)– 250, 500, 700, 850, 925, Surface

– N.B. Be careful of the color scales (no user control over this)

Mesocyclonic 250mb

Mesocyclonic 500mb

Mesocyclonic 700mb

Mesocyclonic 700mb

Mesocyclonic 700mb

Mesocyclonic 850mb

Mesocyclonic 850mb

Mesocyclonic 850mb

Mesocyclonic 925mb

Mesocyclonic 925mb

Mesocyclonic 925mb

Mesocyclonic Surface

QLCS 250mb

QLCS 500mb

QLCS 700mb

QLCS 700mb

QLCS 700mb

QLCS 850mb

QLCS 850mb

QLCS 850mb

QLCS 925mb

QLCS 925mb

QLCS 925mb

QLCS Surface

MesocyclonicMesocyclonic QLCSQLCS

COMPARISONS

`

~5.55 C/km~5.74 C/km

Upper Level Features

• Mesocyclonic– Relatively lower-

amplitude, neutral to positively tilted shortwave trough over Upper Midwest

• QLCS– Relatively higher-

amplitude, negatively tilted shortwave trough over western Great Lakes region

Surface Features

• Mesocyclonic

– Surface low pressure centered over western PA

– Moist, warm sector over entire forecast area

• QLCS

– Surface low pressure centered over northern Michigan

– Negatively tilted surface trough encroaching on forecast area

– Moist airmass along and east of Blue Ridge

Wind Field Features

• Mesocyclonic

– Right entrance region of upper jet

– Zonal 850mb speed maximum across Carolinas (relative southward position)

– Balanced dipole in meridional component of 700mb, 850mb, 925mb winds

– Relatively weaker wind speeds

• QLCS

– Left exit region of upper jet

– Zonal 850mb speed maximum across central Virginia (relative northward position)

– Positive bias to structure of 700mb, 850mb, 925mb meridional wind field

– Relatively stronger wind speeds

Thermodynamic Features

• Mesocyclonic

– Steeper lapse rates

– Slightly lower relative humidity (owing to heating of warm sector?)

– Relatively warmer low-level temperatures owing to seasonal aspect of event distribution?

• QLCS

– Weaker lapse rates

– Slightly higher relative humidity (owing to cloud cover in strongly forced environment?)

– Relatively cooler low-level temperatures owing to seasonal aspect of event distribution?

Questions/References

QUESTIONS and COMMENTS?

email: matthew.kramar@noaa.gov

• Coniglio, Michael C., Harold E. Brooks, Steven J. Weiss, Stephen F. Corfidi, 2007: Forecasting the Maintenance of Quasi-Linear Mesoscale Convective Systems. Wea. Forecasting, 22, 556-570.

• Kalnay, E. and Coauthors, 1996: The NCEP/NCAR Reanalysis 40-year Project. Bull. Amer. Meteor. Soc., 77, 437-471.

• National Climatic Data Center, 2010: NCDC NEXRAD Data Inventory. [Database Online]

• National Climatic Data Center, 2010: NCDC Storm Event Archive. [Database Online]