nicholas d. metz and lance f. bosart department of atmospheric and environmental sciences

Synoptic and Mesoscale Conditions associated with Persisting and

Dissipating Mesoscale Convective Systems that Cross Lake Michigan

Nicholas D. Metz and Lance F. Bosart

Department of Atmospheric and Environmental Sciences

University at Albany/SUNY, Albany, NY 12222

E-mail: nmetz@atmos.albany.edu

Support provided by the NSF ATM–0646907

12th Northeast Regional Operational Workshop

Albany, NY

3 November 2010

Motivation

Johns and Hirt (1987) Augustine and Howard (1991)

• Great Lakes region is an area of frequent MCS (MCC and derecho) activity– Important to understand MCS behavior upon crossing the Great Lakes

Frequency of Derechos MCC Occurrences

1986

NOWrad Areal Coverage ≥45 dBZ

I II IIIIII

0

NOWrad Areal Coverage ≥45 dBZ

0

Background

Graham et al. (2004)

68%24%

8%

Purpose

• Present a climatological overview of MCSs that encountered Lake Michigan

• Examine composite analyses of MCS environments associated with persisting and dissipating MCSs

• Describe two MCSs, one that persisted and one that dissipated while crossing Lake Michigan, and place them into context of the climatology and composites

MCS Selection Criteria

• Warm Season (Apr–Sep)• 2002–2007

• MCSs in the study:– are ≥(100 50 km) on NOWrad composite reflectivity

imagery– contain a continuous region ≥100 km of 45 dBZ echoes – meet the above two criteria for >3 h prior to crossing

Lake Michigan

100 km

50 km

Climatology of MCSs

• MCSs persisted upon crossing Lake Michigan if they:– continued to meet the two aforementioned reflectivity criteria

– produced at least one severe report

n=110

3.0°C 4.4°C 10.8°C 18.9°C 21.6°C 19.1°C

Monthly Climatological Distributionsn=110

LM LWT Climo

Hourly Climatological Distributionsn=110

Synoptic-Scale Composites

• Constructed using 0000, 0600, 1200, 1800 UTC 1.0° GFS analyses

• Time chosen closest to intersection with Lake Michigan– If directly between two analysis times, earlier time

chosen

• Composited on MCS centroid and moved to the average position

Dynamic Persist vs. Dissipate

Persist Dissipate

200-hPa Heights (dam), 200-hPa Winds (m s-1), 850-hPa Winds (m s-1)

n=17 n=31m s−1

m s−1

200-hPa

850-hPa

Dynamic Persist vs. DissipateCAPE (J kg-1), 0–6 km Shear (barbs; m s-1)

Persist Dissipate

n=17 n=31

J kg−1CAPE

Differences Significant to 99.9th Percentile

850-hPa Wind Climatology

n=110

Source: NARR

Downstream CAPE/Shear Climatology

n=54 Source: UAlbany sounding archive

CAPE Differences Significant to 95th Percentile

DTX

18 June 2010 - persist

24 June 2003 - dissipate

Case Studies – Bow Echoes

9 out of 13 bow echoes (69%) persisted compared with 47 out of 110 (43%) total MCSs in the climatology

MCS

1800 UTC 18 June 10 - persist

Source: UAlbany Archive

1000 UTC 24 June 03 - dissipate

MCSSource: NOWrad

Composites

Source: UAlbany Archive

MCS

MCS Source: NOWrad Composites

2000 UTC 18 June 10 - persist

1200 UTC 24 June 03 - dissipate

Source: UAlbany Archive

MCS

MCSSource: NOWrad

Composites

2200 UTC 18 June 10 - persist

1400 UTC 24 June 03 - dissipate

Source: UAlbany Archive

MCS

Source: NOWrad Composites

0000 UTC 18 June 10 - persist

1600 UTC 24 June 03 - dissipate

2000 UTC 18 June 10 - persist

SLP (hPa), Surface Temperature (C), and Surface Mixing Ratio (>18 g kg-1)

20

23

26

29

32

18

08

04

1216

cold pool boundary

1200 UTC 24 June 03 - dissipate

SLP (hPa), Surface Temperature (C), and Surface Mixing Ratio (>18 g kg-1)

20

18

08

12

1623

20

cold pool boundary

2200 UTC 18 June 10 - persist

Source: 20-km RUC

1400 UTC 24 June 03 - dissipate200-hPa Heights (dam), 200-hPa Winds (m s-1), 850-hPa Winds (barbs; m s-1)

CAPE (J kg-1), 0–6 km Shear (barbs; m s-1)

2200 UTC 18 June 10 - persist 1400 UTC 24 June 03 - dissipate

Source: 20-km RUC

cold pool cold pool

B

B’ B’

B’

B

B

B’

2000 UTC 2200 UTC

∆ (K), (K), Wind (m s-1)

600

700

800

900

B

975-hPa ∆ (K), 0–3-km Shear (m s-1)

2-h differences at 2200 UTC 18 June 10 - persist

B’

B

ACARS sounding at 2208 UTC 18 June 10 - persist

900 hPa

975-hPa ∆ (K), 0–3 km Shear (m s-1)

Descent sounding from Madison, WI

T, Td, p

°C

Rockford, Illinois meteogram - persist

Source: UAlbany Archive

975-hPa ∆ (K), 0–3 km Shear (m s-1)

hPa

°C Buoy 45007

T=2.9°C

Source: NDBC

Buoy meteogram - persist975-hPa ∆ (K), 0–3 km Shear (m s-1)

hPaTair, Twater, p

Lake Interactions

LWA – South Haven

2130 Z 2200 Z

T, Td, p

2-h differences at 1300 UTC 23 June 03 - dissipate

cold pool cold pool

B

B’ B’

B’

B

B

B’

1100 UTC 1300 UTC

975-hPa ∆ (K), 0–3-km Shear (m s-1) ∆ (K), (K), Wind (m s-1)

600

700

800

900

B

12 Z - GRB

T, Td, p°C

Oshkosh, Wisconsin meteogram - dissipate

Source: UAlbany Archive

975-hPa ∆ (K), 0–3 km Shear (m s-1)

hPa

°C

Buoy 45007

T=3.4°C

Source: NDBC

Buoy meteogram - dissipate975-hPa ∆ (K), 0–3 km Shear (m s-1)

hPaTair, Twater, p

Later Season

Differences Significant to 99th Percentile

Surface-Inversion Climatology

T5m - TSfc

n=97

Source: NDBC

Conclusions – Climatology/Composite

• MCSs persisted 43% of the time (47 of 110 MCSs) upon crossing Lake Michigan during warm seasons of 2002–2007

• MCSs persisted during all months and hours but favored July and August and evening and overnight

• MCSs persisted with large downstream CAPE/shear and strong 850-hPa winds and near-surface lake inversions (non-bow echoes)

• MCSs persisted with a greater frequency as organizational structure increased

Conclusions – Case Studies

• Compared with the MCS that dissipated, the MCS that persisted had:– a deeper, more robust convective cold pool– a near-surface lake inversion of ~equal strength– increased downstream CAPE/shear and a stronger 850-hPa low-

level jet stream

• In these case studies, (and with other bow echoes in the climatology), persistence/dissipation over Lake Michigan appears to be a function of environmental conditions and NOT interactions with Lake Michigan

Organizational Type

n=110

33.3% 45.7%

69.2%