March 14, 2001 Bow Echo in Southeast

Texas – AMid-Altitude Radial Convergence Case

StudyPaul Lewis II

Objectives

1. Brief overview of Mid-Altitude Radial Convergence (MARC)

2. Summary of the synoptic and meso-scale pattern for March 14, 2001

3. How the MARC signature analysis can be utilized to pinpoint warnings

4. Questions or comments?

• A MARC analysis is a tool that can be utilized with other severe weather analysis techniques

• The MARC signature can help pinpoint locations of strongest surface winds

• Useful in understanding the model of a bow echo that generates damaging downbursts

MARC Overview

MARC Overview

• From Gary Schmocker & Ron Przybylinski at WFO St. Louis:– “The MARC velocity signature is a Doppler

radar-velocity based precursor towards forecasting the initial onset of damaging straight-line winds in a linear Quasi Linear Convective System (QLCS) or bowing convective system.”

– http://www.crh.noaa.gov/lsx/?n=marc_signature

• More from Schmocker & Przybylinski:– MARC signature = Vmaxin + Vmaxout

– Look for MARC signature of 24 m/s (~50 kts) along 3 to 6 radials

– Enhanced wind damage possible with a local area of enhanced radial convergence of 35 to 40 m/s (70 to 80 knots) within the larger MARC signature

MARC Overview

MARC Overview

• From Gary Schmocker & Ron Przybylinski - WFO St. Louis and Yeong-Jer Lin – SLU

• See: http://www.crh.noaa.gov/lsx/science/marc/newmarc.php

MARC Overview

• From Gary Schmocker & Ron Przybylinski - WFO St. Louis and Yeong-Jer Lin – SLU

• See: http://www.crh.noaa.gov/lsx/science/marc/newmarc.php

Summary of the Synoptic and Meso-Scale Pattern for March 14, 2001

• 2 bow echoes affected SE Texas

• 1st produced damage west of Houston (mobile home example)

• 2nd moved over the radar site. . .Focus of this case study

Paul Lewis NWS HGX

Meso/Synoptic Scale Overview

• Ongoing convection from the previous day: Soundings a worked over air mass but with a downburst potential

SoundingsCRP at 12 UTC 14 March 2001

Low-Level Jet forming?

Soundings LCH at 12 UTC 14 March 2001

One item stuck out

after the post-storm

analysis: DCAPE!

Low-Level Jet? – No!

Station LI KI PW CAPE CIN DCAPE 700-500 LR

CRP 3.1 23.3 1.16 NA NA 1110 -6.8

FWD 4.7 31.7 0.93 NA NA 501 -5.5

LCH 7.5 14.7 0.99 NA NA 1163 -4.9

SHV 10.2 15.1 0.77 NA NA 901 -5.1

12 UTC 14 March 2001

Thermodynamic Parameters

• Downdraft CAPE (DCAPE) – An indicator of downburst strength potential

• DCAPE computed by RAOB using the “density weighted 6 km method”

• DCAPE reference: Gilmore, M. S., and Wicker, L. J., 1997: The influence of midtropospheric dryness on supercell morphology and evolution. Mon. Wea. Rev., 126, 943–958.

• Ongoing convection from the previous day: Soundings a worked over air mass but with a downburst potential

• Active pattern with an approaching upper trough

• Increasing low-level moisture

• Increasing instability

Meso/Synoptic Scale Overview

Developing Diffluent Flow Aloft12 UTC 3/14 250 mb 00 UTC 3/15 250 mb

Images courtesy of the Storm Prediction Center Map Archives http://w1.spc.woc.noaa.gov/obswx/maps/

Approaching Upper Trough12 UTC 3/14 500 mb 00 UTC 3/15 500 mb

Images courtesy of the Storm Prediction Center Map Archives http://w1.spc.woc.noaa.gov/obswx/maps/

Mid-Level Dry Air Punch12 UTC 3/14 700 mb 00 UTC 3/15 700 mb

Images courtesy of the Storm Prediction Center Map Archives http://w1.spc.woc.noaa.gov/obswx/maps/

Low-Level Moisture Increase12 UTC 3/14 850 mb 00 UTC 3/15 850 mb

Images courtesy of the Storm Prediction Center Map Archives http://w1.spc.woc.noaa.gov/obswx/maps/

Low-Level Moisture Increase12 UTC 3/14 925 mb 00 UTC 3/15 925 mb

Images courtesy of the Storm Prediction Center Map Archives http://w1.spc.woc.noaa.gov/obswx/maps/

SoundingsCRP at 00 UTC 15 March 2001

SoundingsLCH at 00 UTC 15 March 2001

Low-Level Jet – Yes!

Event Evolution

2059 UTC 14 March 2001

Developing bow echo

Previous bow echo

Utilizing MARC to Pinpoint Warnings

• High situational awareness was present during the event due to damage reports received during the 1st bow echo

• MARC analysis was conducted during the post-storm review

• Location of MARC signatures can help pinpoint potential wind damage areas

• County-based warnings were issued during the event– The technique can greatly aid in issuing

modern storm-based warnings– Can be utilized to update warnings (SVS)

Conclusions from Post-Storm Analysis

2.4˚ 5.9˚ 9.3˚

6-Panel Method – Imagine “All Tilt” or “4-Panel”

Developing MARC

Developed MARC Signature at 2208 UTC

2.4˚ 5.9˚ 9.3˚

Developed MARC Signature at 2223 UTC

2.4˚ 5.9˚ 9.3˚• MARC signature is a bit tough

to see – probably better in the AWIPS environment

• Cross sections were seen to be the best way to view the MARC during the post-storm analysis

Cross Section Location

• Following slides are cross sections of Reflectivity and Storm Relative Motion

• The cross sections were taken WSW of the radar site

Cross SectionsNote. . .Radar site to the left – directional sense reversed

2158 UTC 14 March 2001

• Developing MARC signature ~ 18,000 ft & 40 nm WSW HGX

• About 39 knots – 32 minutes before 1st wind damage

Cross SectionsNote. . .Radar site to the left – directional sense reversed

2203 UTC 14 March 2001

• Developed MARC signature ~ 14,000 ft & 40 nm WSW HGX

• About 52 to 65 knots – 27 minutes before 1st wind damage

Cross SectionsNote. . .Radar site to the left – directional sense reversed

2208 UTC 14 March 2001

• MARC signature 12,000 – 14,000 feet & 30 nm WSW HGX

• Around 65 Knots – 22 minutes prior to the 1st wind damage

Cross SectionsNote. . .Radar site to the left – directional sense reversed

2214 UTC 14 March 2001

• MARC signature 8,000 – 14,000 feet & 22 nm WSW HGX

• 78 and 91 knots (16 minutes prior) – SVS to update warning?

Cross SectionsNote. . .Radar site to the left – directional sense reversed

2224 UTC 14 March 2001

• MARC signature > 65 knots (4 minutes prior)

• Last MARC signature before the 1st damaging wind report

MARC & Damage Locations

• Note the pattern of severe events & MARC locations

• MARC times listed:– 2208 UTC (1608 LST)– 2213 UTC (1613 LST)– 2218 UTC (1618 LST)– 2223 UTC (1623 LST)

Highlighted Wind Reports

Note. . .LST = UTC – 6• 1555 LST – Trees and street signs down in Pearland• 1625 LST – 80 mph est. wind gust in Friendswood• 1630 LST – Wind damage in Alvin• 1636 LST – 62 mph gust at NWS• 1640 LST – Tornado report in Sante Fe• 1645 LST – 65 mph gust at Texas City PD• 1700 LST – Wind damage on Galveston Island

Wind Damage near KHGX

Paul Lewis NWS HGX

Paul Lewis NWS HGX

Questions or Comments?

Paul LewisNational Weather Service1353 FM 646 Rd WSuite 202Dickinson, TX 77539

e-mail: Paul.Lewis@noaa.gov

Sunset view of the backside of 14 March 2001 bow echo at NWS HGX Paul Lewis NWS HGX