March 14, 2001 Bow Echo in Southeast Texas – A Mid-Altitude Radial Convergence Case Study Paul Lewis II

Objectives 1.Brief overview of Mid-Altitude Radial Convergence (MARC) 2.Summary of the synoptic and meso- scale pattern for March 14, 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

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.” –

More from Schmocker & Przybylinski: –MARC signature = Vmax in + Vmax out –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

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

MARC Overview From Gary Schmocker & Ron Przybylinski - WFO St. Louis and Yeong-Jer Lin – SLU See:

Summary of the Synoptic and Meso- Scale Pattern for March 14, bow echoes affected SE Texas 1 st produced damage west of Houston (mobile home example) 2 nd 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

Soundings CRP 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!

StationLIKIPWCAPECINDCAPE LR CRP NA FWD NA LCH NA SHV NA 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 Aloft 12 UTC 3/ mb 00 UTC 3/ mb Images courtesy of the Storm Prediction Center Map Archives

Approaching Upper Trough 12 UTC 3/ mb 00 UTC 3/ mb Images courtesy of the Storm Prediction Center Map Archives

Mid-Level Dry Air Punch 12 UTC 3/ mb 00 UTC 3/ mb Images courtesy of the Storm Prediction Center Map Archives

Low-Level Moisture Increase 12 UTC 3/ mb 00 UTC 3/ mb Images courtesy of the Storm Prediction Center Map Archives

Low-Level Moisture Increase 12 UTC 3/ mb 00 UTC 3/ mb Images courtesy of the Storm Prediction Center Map Archives

Soundings CRP at 00 UTC 15 March 2001

Soundings LCH 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 1 st 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 Sections Note...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 1 st wind damage

Cross Sections Note...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 1 st wind damage

Cross Sections Note...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 1 st wind damage

Cross Sections Note...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 Sections Note...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 1 st 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 – 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

Questions or Comments? Paul Lewis National Weather Service 1353 FM 646 Rd W Suite 202 Dickinson, TX Sunset view of the backside of 14 March 2001 bow echo at NWS HGX Paul Lewis NWS HGX