The 1 November 2004 tornadic QLCS event over southwest Illinois Ron W. Przybylinski Science and Operations Officer National Weather Service – St. Louis NOAA’s National Weather Service WFO LSX 2008 Winter Weather Workshop

01 November 2004 QLCS Convective lines which form and rapidly move across the Mid-Mississippi Valley region during the transitional season can be challenging to the warning forecaster. Some questions we ask: 1) Will the event be only comprised of damaging winds? or 2) Is there a tornado threat? Will the tornado threat be confined to one part of a bowing segment or are there two areas of concern? Convective lines which form and rapidly move across the Mid-Mississippi Valley region during the transitional season can be challenging to the warning forecaster. Some questions we ask: 1) Will the event be only comprised of damaging winds? or 2) Is there a tornado threat? Will the tornado threat be confined to one part of a bowing segment or are there two areas of concern?

01 November 2004 QLCS During the early part of the afternoon of 01 November 2004 a convective line developed over parts of southeast Missouri and southwest Illinois and produced two weak tornadoes; 1) first having a short path 5 to 7 miles southwest of Sparta and 2) the second damage path from 2 miles southwest of Sparta through the town of Sparta Illinois. A number of large trees were damaged at the Sparta Country Club and damage to a number of building including the steeple of a Church in downtown Sparta Il.

Outline of the case The first part of presentation will cover the pre and near storm environment on 1 November Will be using SPC Mesoscale analysis output to show the near storm environment conditions. WSR-88D Doppler radar analysis on the event. Comparison of this case to another case. Summary The first part of presentation will cover the pre and near storm environment on 1 November Will be using SPC Mesoscale analysis output to show the near storm environment conditions. WSR-88D Doppler radar analysis on the event. Comparison of this case to another case. Summary

Large-scale Environment 500 mb 1200 UTC 11/01/ mb 1200 UTC

1800 UTC Surface map

Soundings at 1200 UTC 01 Nov 2004 KSGF KLZK ML CAPE 1318 J kg -1 ML CIN -85 J kg -1 0 – 6 km shear - 27 m s -1 0 – 3 km shear - 15 m s -1

Bloomfield MO Profiler ( west of Cape Girardeau ) Bulk Shear 0 – 6 km 18 m s -1 0 – 3 km 15 m s -1

SPC Mesoscale Analysis MUCAPE – 1800 UTCSBCAPE – 1800 UTC

SPC Mesoscale Analysis Mean Parcel LCL Height

SPC Mesoscale Analysis 0-6 km Shear 25 – 30 m s km Shear 12 – 15 m s -1

SPC Mesoscale analysis 0-1 km Storm Relative Helicity m 2 s km Storm Relative Helicity 200 – 250 m 2 s -2

WSR-88D Radar Imagery at 1934 UTC Base Reflectivity Storm-relative velocity

WSR-88D radar imagery from KLSX at 1944 UTC Reflectivity image showing Quasi-Linear Convective System (QLCS) Storm-relative velocity image (SRM)

Radar Imagery from KLSX at 1949 UTC Nearly Linear convective segment is observed – not much bowing. The TVS was located in the storm’s forward reflectivity gradient region.

Reflectivity / Velocity Cross-sections 1949 UTC

Radar Imagery from KLSX at 1954 UTC Mesovortex 1 continues to remain partially embedded within the reflectivity gradient region. Rotational velocity (Vr) values at 0.5° slice was 18 m s -1 (36 kts).

Reflectivity – Velocity Cross-sections 1954 UTC

Radar imagery for 1959 UTC Mesovortex 1 approaches Sparta Illinois. MV 1 remains partially embedded within the higher reflectivity. Magnitude of Vr remains at 18 m s -1 (36 kts) – 0.5° slice.

Radar imagery for 2004 UTC MV 1 is now totally embedded with the high reflectivity core region. Vr value at 0.5° elevation slice dropped to 17 m s-1.

Radar imagery at 2014 UTC MV 1 enters its later stages and begins to weaken as it crosses into southwest Washington County. MV 4 is a short-lived mesovortex.

Map of the track of MV 1 Source of damage reports: Storm Data

Rotational Velocity trace MV 1 Magnitudes of Vr values are in m s -1 mulitply by 2 to get values in knots.

MV 1 Core Diameter Trace

Feb 11, 1999 – Comparison case

KLSX Reflectivity / SRM Velocity 1952 UTC 11 Feb 1999 Isolated cells merging near the apex of the southern bow echo.

Rotational Velocity MV 2

Rotational Velocity Trace MV-4

Summary We reviewed the 1 November 2004 tornadic QLCS as it moved across parts of southwest Illinois. Pre and near storm environment low CAPE – moderate to high shear Mesovortex rapidly formed along a shear axis Two weak tornadoes (F0) formed about 12 – 14 min after the initial identification of MV1. Strongest rotation was confined within the lowest 2 km of MV 1. Tornadoes preceded the deepening and strengthening of MV1 We reviewed the 1 November 2004 tornadic QLCS as it moved across parts of southwest Illinois. Pre and near storm environment low CAPE – moderate to high shear Mesovortex rapidly formed along a shear axis Two weak tornadoes (F0) formed about 12 – 14 min after the initial identification of MV1. Strongest rotation was confined within the lowest 2 km of MV 1. Tornadoes preceded the deepening and strengthening of MV1

Summary cont MV 1 core diameter dropped to 2.2 km just prior to tornado touchdown. Feb 11, 1999 – second case also showed strongest low-level rotation below 2 km. Tornadoes caused (F1 and F2) damage with this case. Damage survey was conducted during occasional light snow showers and squalls (temps - low 30s). MV 1 core diameter dropped to 2.2 km just prior to tornado touchdown. Feb 11, 1999 – second case also showed strongest low-level rotation below 2 km. Tornadoes caused (F1 and F2) damage with this case. Damage survey was conducted during occasional light snow showers and squalls (temps - low 30s).