Maintenance of a Mesoscale Convective System over Lake

Michigan

Nicholas D. Metz and Lance F. Bosart

Department of Earth and Atmospheric Sciences

University at Albany/SUNY, Albany, NY 12222

E-mail: nmetz@atmos.albany.edu

Support provided by the NSF ATM-0646907

10th Northeast Regional Operational Workshop

Albany, New York

6 November 2008

Motivation

• MCS maintained its identity crossing Lake Michigan while intense supercell dissipated (will focus on MCS)

associated with supercell

associated with MCS/MCS boundary

MCS and associated

convection not well forecast

by large-scale models

Purpose

• Describe synoptic/mesoscale flow evolution leading to convection that was not well forecast by the large-scale models

• Explain why a severe weather-producing MCS was maintained while crossing Lake Michigan

• Discuss cold-pool-induced boundaries that focused additional severe weather in the wake of the MCS

Datasets

• 20-km 20-km RUC analyses (50 vertical levels)• NCDC NEXRAD level 3 radar base reflectivity• NPVU 24-h QPE images• RAP infrared and water vapor satellite images • University at Albany surface data archives• University at Albany sounding archives

Radar Evolution

1145 UTC

1102 UTC 7 June 08

MCS forms near

northeastern extent of surface

boundary

warm advection to east of MCS

previous MCS convection

15–20 cm

24-hr QPE ending 1200 UTC 7 June 08

MCS

1404 UTC 7 June 08

1415 UTC

boundary extending eastward associated

with cold pool (will focus here)

L

1701 UTC 7 June 08

1715 UTC

L

boundary associated with cold pool from

previous MCS

2004 UTC 7 June 08

2015 UTC

L

supercell

MCS

development along cold-pool-induced

boundary

2105 UTC 7 June 08

2115 UTC

L

2200 UTC 7 June 08

2215 UTC

L

2304 UTC 7 June 08

2315 UTC

L

supercell

MCS

convection along cold-pool-induced

boundary

0001 UTC 8 June 08

0015 UTC

0104 UTC 8 June 08

0115 UTC

MCS

0302 UTC 8 June 08

0315 UTC

0600 UTC 8 June 08

0615 UTC

8–12 cm

24-hr QPE ending 1200 UTC 8 June 08

Upper-level Overview

1500 UTC 7 June 08200-hPa Heights (dam), 200-hPa Wind (m s-1), 850-hPa Wind (barbs; m s-1)

LLJ & warm

advection

1515 UTCshortwave

1800 UTC 7 June 08200-hPa Heights (dam), 200-hPa Wind (m s-1), 850-hPa Wind (barbs; m s-1)

shortwave

1815 UTC

2100 UTC 7 June 08200-hPa Heights (dam), 200-hPa Wind (m s-1), 850-hPa Wind (barbs; m s-1)

2115 UTC

0000 UTC 8 June 08200-hPa Heights (dam), 200-hPa Wind (m s-1), 850-hPa Wind (barbs; m s-1)

0015 UTC

Mesoscale Evolution and Convective Development

1600 UTC 7 June 08CAPE (J kg-1), 0–1 km Shear (m s-1), 0–6 km Shear (barbs; m s-1)

MCS

previous convection

1600 UTC 7 June 08

20 20

23

26

2923

26

04

08

12

16 20

18

cold-pool-induced

boundary

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

MCS

previous convection

cold-pool-induced

boundary

1600 UTC 7 June 08

20 20

23

26

2923

26

04

08

12

16 20

18

Dry Air

~900 J kg-1

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

1800 UTC 7 June 08CAPE (J kg-1), 0–1 km Shear (m s-1), 0–6 km Shear (barbs; m s-1)

1800 UTC 7 June 08

~3300 J kg-1

DVN-1800 UTC

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

1800 UTC 7 June 08

Frontogenesis

Surface Frontogenesis (ºC 100 km-1 3h-1), Surface Winds (barbs; m s-1)

2000 UTC 7 June 08

MCS

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

2000 UTC 7 June 08

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)

cold-pool-induced

boundary

warm advection

cold-pool-induced

boundary

2000 UTC 7 June 08

23

26

26

23

20

29

32

29

26

32

04

08

12

1618

supercells2004 UTC

cold-pool-induced

boundary

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

2200 UTC 7 June 08

convection along cold-pool-induced boundary

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

3-h e differences at 2300 UTC 7 June 08950-hPa ∆e (K), 0–3-km Shear (m s-1) ∆e (K), (K), Wind (m s-1)

cold poolcold pool

A

A’ A’

A’

A

A

A A’

2000 UTC 2300 UTC

200 0

400

600

800

950-hPa ∆e (K), 0–3 km Shear (m s-1)

MSN

T, Td, p

ºC hPa

3-h e differences at 2300 UTC 7 June 08

950-hPa ∆e (K), 0–3 km Shear (m s-1)

3-h e differences at 2300 UTC 7 June 08

ºC hPa

T, p

Buoy 45007

0000 UTC 8 June 08CAPE (J kg-1), 0–1 km Shear (m s-1), 0–6 km Shear (barbs; m s-1)

0000 UTC 8 June 08

18

2323

26

29

29

04

0812

16

20

cold-pool-induced

boundary

MCS

convection along cold-pool-induced boundary

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

18

2323

26

29

29

04

0812

16

0000 UTC 8 June 08

20

cold-pool-induced

boundary

MCS

convection along cold-pool-induced boundary

Surface Frontogenesis (ºC 100 km-1 3h-1)

0000 UTC 8 June 08PV (PVU), Pressure (hPa), Wind (barbs; m s-1) on 305 K isentrope

isentropic ascent

B’

B

0000 UTC 8 June 08PV (PVU), Pressure (hPa), Wind (barbs; m s-1) on 305 K isentrope

isentropic ascent

B’

B

ILX

DVNILX

DVN

LFC=891 hPa

LFC=885 hPa

0000 UTC 8 June 08Convergence ( 10-5 s-1), (K), ( 10-5 s-1), Wind (barbs; m s-1)

cold-pool-induced

boundary

500

750

1000B B’

Evolution and Dissipation of Supercell

2200 UTC 2300 UTC

0000 UTC 0100 UTC

2330 UTC

incipient supercell

0300 UTC 8 June 08CAPE (J kg-1), 0–1 km Shear (m s-1), 0–6 km Shear (barbs; m s-1)

Concluding Hypothesis

W E

z

x

Strong Shear

3 km

time = t time = t + ∆T

Cold Pool Circ.

Shear Circ.

– ++ W

Strong Shear

3 km

Cold Pool Circ.

Shear Circ.

– +

• MCS developed in high shear environment and created strong cold pool in association with dry air aloft

• Vigorous ascent was maintained over lake as MCS cold pool depth >> lake cold pool depth and ascent was aided by: – ageostrophic circulation associated with frontogenesis

– strong low-level jet stream advecting warm/unstable air – weak short-wave trough

E

Conclusions

• MCS cold pool created quasi-stationary boundary that:– increased low-level shear (better supercell environment)

– acted as a warm front (focus for isentropic ascent)

• Illinois supercell dissipated over Lake Michigan where water temperature was near 8ºC

Cold-Pool-Induced

Boundary

Supercells

SSW Flow and Isentropic Ascent

Supercell Track

MCS Track

Cold Lake

Boundary from previous MCS

convection