A “Survey” of Tornadoes and their Environments in the WFO Sterling, VA Forecast Area Matthew R. Kramar Senior Forecaster, WFO LWX Kyle M. Olmstead Student 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 (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 ( )

Number of Days of Tornado Occurrence ( )

Number of Days of Mesocyclonic Tornado Occurrence

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 850mb

Mesocyclonic 925mb

Mesocyclonic Surface

QLCS 250mb

QLCS 500mb

QLCS 700mb

QLCS 850mb

QLCS 925mb

QLCS Surface

MesocyclonicQLCS COMPARISONS

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~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? 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, Kalnay, E. and Coauthors, 1996: The NCEP/NCAR Reanalysis 40-year Project. Bull. Amer. Meteor. Soc., 77, National Climatic Data Center, 2010: NCDC NEXRAD Data Inventory. [Database Online] National Climatic Data Center, 2010: NCDC Storm Event Archive. [Database Online]