synoptic and mesoscale conditions associated with persisting and dissipating mesoscale convective...
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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: [email protected]
Support provided by the NSF ATM–0646907
12th Northeast Regional Operational Workshop
Albany, NY
3 November 2010
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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
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NOWrad Areal Coverage ≥45 dBZ
I II IIIIII
0
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NOWrad Areal Coverage ≥45 dBZ
0
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Background
Graham et al. (2004)
68%24%
8%
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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
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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
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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
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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
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Hourly Climatological Distributionsn=110
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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
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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
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Dynamic Persist vs. DissipateCAPE (J kg-1), 0–6 km Shear (barbs; m s-1)
Persist Dissipate
n=17 n=31
J kg−1CAPE
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Differences Significant to 99.9th Percentile
850-hPa Wind Climatology
n=110
Source: NARR
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Downstream CAPE/Shear Climatology
n=54 Source: UAlbany sounding archive
CAPE Differences Significant to 95th Percentile
DTX
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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
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MCS
1800 UTC 18 June 10 - persist
Source: UAlbany Archive
1000 UTC 24 June 03 - dissipate
MCSSource: NOWrad
Composites
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Source: UAlbany Archive
MCS
MCS Source: NOWrad Composites
2000 UTC 18 June 10 - persist
1200 UTC 24 June 03 - dissipate
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Source: UAlbany Archive
MCS
MCSSource: NOWrad
Composites
2200 UTC 18 June 10 - persist
1400 UTC 24 June 03 - dissipate
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Source: UAlbany Archive
MCS
Source: NOWrad Composites
0000 UTC 18 June 10 - persist
1600 UTC 24 June 03 - dissipate
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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
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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
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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)
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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
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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
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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
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T, Td, p
°C
Rockford, Illinois meteogram - persist
Source: UAlbany Archive
975-hPa ∆ (K), 0–3 km Shear (m s-1)
hPa
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°C Buoy 45007
T=2.9°C
Source: NDBC
Buoy meteogram - persist975-hPa ∆ (K), 0–3 km Shear (m s-1)
hPaTair, Twater, p
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Lake Interactions
LWA – South Haven
2130 Z 2200 Z
T, Td, p
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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
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T, Td, p°C
Oshkosh, Wisconsin meteogram - dissipate
Source: UAlbany Archive
975-hPa ∆ (K), 0–3 km Shear (m s-1)
hPa
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°C
Buoy 45007
T=3.4°C
Source: NDBC
Buoy meteogram - dissipate975-hPa ∆ (K), 0–3 km Shear (m s-1)
hPaTair, Twater, p
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Later Season
Differences Significant to 99th Percentile
Surface-Inversion Climatology
T5m - TSfc
n=97
Source: NDBC
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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
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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
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Organizational Type
n=110
33.3% 45.7%
69.2%