The Effects of Lake Michigan on Mature Mesoscale Convective Systems Nicholas D. Metz and Lance F....

The Effects of Lake Michigan on Mature Mesoscale Convective

Systems

Nicholas D. Metz and Lance F. Bosart

Department of Atmospheric and Environmental Sciences

University at Albany/SUNY, Albany, NY 12222

E-mail: [email protected]

Support provided by the NSF ATM–0646907

18th Great Lakes Operational Meteorology Workshop

Toronto, Ontario

23 March 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 behavior of MCSs when crossing the Great Lakes

Frequency of Derechos MCC Occurrences

1986

Areal Coverage ≥45 dBZ

I II IIIIII

0

Areal Coverage ≥45 dBZ

0

Background

Graham et al. (2004)

68%24%

8%

Purpose

• Present a climatology 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 the lake if they:– continued to meet the two aforementioned reflectivity criteria

– produced at least one severe report

n=110

PersistDissipate

Intersection Time after Formation

n=110

Persist Dissipate

Monthly Distributions

n=110

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

Persist Dissipate

Hourly Distributions (UTC)

n=110

Persist Dissipate

Synoptic-Scale Composites

• Constructed using 0000, 0600, 1200, 1800 UTC 1° 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 vs. Progressive

Dynamic Progressive

Johns (1993)

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

Progressive Persist vs. Dissipate200-hPa Heights (dam), 200-hPa Winds (m s-1), 850-hPa Winds (m s-1)

Persist Dissipate

n=30 n=32m s−1

m s−1

200-hPa

850-hPa

Progressive Persist vs. Dissipate

n=32n=30

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

Persist Dissipate

n=30 n=32

J kg−1CAPE

7–8 June 2008 - persist

4–5 June 2005 - dissipate

Case Studies

MCS 2105 UTC 7 June 08 - persist

Source: UAlbany Archive

1600 UTC 4 June 05 - dissipate

MCSSource: NOWrad

Composites


MCS

MCS

Source: NOWrad Composites

2304 UTC 7 June 08 - persist



MCS

MCS





MCS





23

26

26

23

20

29

32

29

26

32

04

08

12

1618

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


MCS

SLP (hPa), Surface Temperature (C), and Surface Mixing Ratio (>16 g kg-1)


20

23

26

2904

08

12

16

MCS



Source: 20-km RUC

2100 UTC 4 June 05 - dissipate200-hPa Heights (dam), 200-hPa Winds (m s-1), 850-hPa Winds (barbs; m s-1)

Source: 20-km RUC

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

0000 UTC 8 June 08 - persist 2100 UTC 4 June 05 - dissipate

Source: 20-km RUC

4-h differences at 2300 UTC 7 June 08 - persist975-hPa ∆ (K), 0–3-km Shear (m s-1) ∆ (K), (K), Wind (m s-1)

cold pool cold pool

A

A’ A’

A’

A

A

A’

1900 UTC 2300 UTC

600

700

800

900

A

Courtesy: M. Weisman

Weisman and Rotunno (2004)

975-hPa ∆ (K), 0–3-km Shear (m s-1)

cold pool cold pool

A’

A

A

A’

2300 UTC

A 905 hPa

4-h differences at 2300 UTC 7 June 08 - persist

MSN

T, Td, p

°C hPa

Madison, Wisconsin meteogram975-hPa ∆ (K), 0–3 km Shear (m s-1)


°C hPa

Tair, Twater, p

Buoy 45007

975-hPa ∆ (K), 0–3 km Shear (m s-1)

T=6.2°C

Source: NDBC

Buoy meteogram

2-h differences at 1900 UTC 4 June 05 - dissipate

cold pool cold pool

B

B’ B’

B’

B

B

B’

1700 UTC 1900 UTC

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

600

700

800

900

B

cold pool cold pool

B’

B

B

B’

975-hPa ∆ (K), 0–3-km Shear (m s-1)

B935 hPa

2-h differences at 1900 UTC 4 June 05 - dissipate

ARR

T, Td, p

°C hPa

Aurora, Illinois meteogram


975-hPa ∆ (K), 0–3 km Shear (m s-1)

°C hPa

Tair, Twater, p

Buoy 45007

T=2.1°C

Source: NDBC

Buoy meteogram975-hPa ∆ (K), 0–3 km Shear (m s-1)

Differences Significant to 99.9th Percentile

850-hPa Wind Climatology

n=110

Persist DissipateSource: NARR

Later Season

Weak LLJ

Differences Significant to 95th Percentile

Surface-Inversion Climatology

T5m - TSfc

n=110

Persist Dissipate Source: NDBC

All Months

Phase Space - Warm Season

Source: NARR/NDBC

n=110

Persist Dissipate

AMJ

JAS

Phase Space - Early Season

Phase Space -Late Season

n=46

n=64

Persist

Dissipate

Dissipate

Persist

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

2002–2007

• MCSs persisted and dissipated at a wide range of times after formation

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

• MCSs persisted with stronger 850-hPa winds and near-surface lake inversions, especially from April to July

Conclusions – Composites/Case Studies

• Compared to MCSs that dissipated, MCSs persisted in environments that contained:– stronger 200-hPa and 850-hPa jet streams– larger amounts of CAPE and 0–6-km shear – similar looking synoptic-scale patterns– stronger, deeper convective cold pools– more stable marine layers

The Effects of Lake Michigan on Mature Mesoscale Convective Systems Nicholas D. Metz and Lance F....

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