The Influence of the Elevated Mixed Layer on Record High Temperatures and Severe Weather Over the...

The Influence of the Elevated Mixed Layer on RecordHigh Temperatures and Severe Weather Over the

Northeast US in April and May 2010

Jason M. Cordeira+, Thomas J. Galarneau, Jr.*, and Lance F. Bosart+

+Department of Atmospheric and Environmental SciencesUniversity at Albany, Albany, NY, USA

*Cooperative Institute for Research in Environmental SciencesUniversity of Colorado at Boulder, Boulder, CO, USA

NSF Support: [email protected]

NROW XII

Wednesday, 3 November 2010

Albany, NY

• Discuss physical processes that contribute to maintenance of an elevated mixed layer (EML) to over the Northeast U.S.

• Discuss EMLs over the Northeast during:– Record high temperatures on 7 April and

26 May 2010– A severe MCS over western New England

on 26−27 May 2010 (complementing Tom Wasula’s talk)

Objectives


• Discuss EMLs over the Northeast during:– Record high temperatures on 7 April and

26 May 2010– A severe MCS over western New England

on 26−27 May 2010

Objectives

EMLs as High Lapse Rates over North America

• Data source: – North American radiosonde network – 1974 to 2007; 12Z data only

• Catalogued: – Continuous 150-hPa layers– Exceeded a lapse rate of −8.0 C km−1

between 925 and 400 hPa

• Warm-season: – Layer-mean θ >30°C

Climatology of high lapse rates (HLRs):

• Intermountain-West U.S. maximum driven by sensible heating over semi-arid elevated terrain

• Maximum develops poleward from Mexico to Colorado between April and July

EMLs as High Lapse Rates over North America

Climatology of high lapse rates (HLRs):

• Poleward and eastward displacement of HLRs from their source region

• ~50% occur in March-April-May

HLRs over the Northeast U.S.: Albany, NY Monthly HLR Frequency (N=33)

• Data source: – North American radiosonde network – 1974 to 2007; 12Z data only

• Catalogued: – Continuous 150-hPa layers– Exceeded a lapse rate of −8.0 C km−1

between 925 and 400 hPa

• Warm-season: – Layer-mean θ >30°C

HLRs over the Northeast U.S.

• Banacos, P. C., and M. L. Ekster, 2010: The association of the elevated mixed layer with significant severe weather events in the Northeastern U.S, Wea. and Forecasting, 25, 1082–1102.

– 7.6% of significant severe weather in the Northeast occurs in association with an EML.

– EML plume originates over the Intermountain West and is transported to the Northeast in subsiding, anticyclonically curved flow.

– Lapse rate advection dominates transport of EML. Illustrated using a scale analysis of the lapse rate tendency equation in height coordinates.

Complementary Research:Fig. 3:All sig. severe 1976-2006

Fig. 8a:3-km trajectories for EML influenced sig. severe

HLRs over the Northeast U.S.: Albany, NY Monthly HLR Frequency (N=15)


• Isolated March-April-May HLRs over Albany, NY (1974−2007)

• Created composite air parcel trajectories from NCEP−NCAR reanalysis

Ending at 500 hPa

−24 h

−48 h

−72 h

Ending at 600 hPa

−24 h

−48 h

−72 h

Ending at 700 hPa

−24 h

−48 h

−72 h

Composite 72-h backward air parcel trajectories:

hPa

0 h

0 h

0 h

Maintenance and destruction of HLRs

d

dt

∂θ∂p

⎛⎝⎜

⎞⎠⎟=−

∂rVa

∂p⎛

⎝⎜⎞

⎠⎟g∇θ −

∂ω∂p

⎛⎝⎜

⎞⎠⎟

∂θ∂p

⎛⎝⎜

⎞⎠⎟+

∂∂p

dθdt

⎛⎝⎜

⎞⎠⎟

Lagrangian tendency = Tilting + Stretching + Differential Diabatic


d

dt

∂θ∂p

⎛⎝⎜

⎞⎠⎟=−

∂rVa

∂p⎛

⎝⎜⎞

⎠⎟g∇θ −

∂ω∂p

⎛⎝⎜

⎞⎠⎟

∂θ∂p

⎛⎝⎜

⎞⎠⎟+

∂∂p

dθdt

⎛⎝⎜

⎞⎠⎟

Maintenance: What processes produce HLR maintenance?

HLR maintained when right-hand side forcing terms are zero or balanceHLR maintenance suggests the local tendency is dominated by advection.

d

dt

∂θ∂p

⎛⎝⎜

⎞⎠⎟=0; 0 =−

∂rVa

∂p⎛

⎝⎜⎞

⎠⎟g∇θ −

∂ω∂p

⎛⎝⎜

⎞⎠⎟

∂θ∂p

⎛⎝⎜

⎞⎠⎟+

∂∂p

dθdt

⎛⎝⎜

⎞⎠⎟



d

dt

∂θ∂p

⎛⎝⎜

⎞⎠⎟=−

∂rVa

∂p⎛

⎝⎜⎞

⎠⎟g∇θ −

∂ω∂p

⎛⎝⎜

⎞⎠⎟

∂θ∂p

⎛⎝⎜

⎞⎠⎟+

∂∂p

dθdt

⎛⎝⎜

⎞⎠⎟

d

dt

∂θ∂p

⎛⎝⎜

⎞⎠⎟=0; 0 =−

∂rVa

∂p⎛

⎝⎜⎞

⎠⎟g∇θ −

∂ω∂p

⎛⎝⎜

⎞⎠⎟

∂θ∂p

⎛⎝⎜

⎞⎠⎟+

∂∂p

dθdt

⎛⎝⎜

⎞⎠⎟

Maintenance: What processes produce HLR maintenance?

Dissipation:What processes produce HLR dissipation?

HLR dissipation for thermally direct circulations, strong low-level ascent, or cessation of strong low-level sensible heating (or deep moist convection)

d

dt

∂θ∂p

⎛⎝⎜

⎞⎠⎟< 0; −

∂rVa

∂p⎛

⎝⎜⎞

⎠⎟g∇θ −

∂ω∂p

⎛⎝⎜

⎞⎠⎟

∂θ∂p

⎛⎝⎜

⎞⎠⎟+

∂∂p

dθdt

⎛⎝⎜

⎞⎠⎟< 0


HLR maintained when right-hand side forcing terms are zero or balanceHLR maintenance suggests the local tendency is dominated by advection.


d

dt

∂θ∂p

⎛⎝⎜

⎞⎠⎟=−

∂rVa

∂p⎛

⎝⎜⎞

⎠⎟g∇θ −

∂ω∂p

⎛⎝⎜

⎞⎠⎟

∂θ∂p

⎛⎝⎜

⎞⎠⎟+

∂∂p

dθdt

⎛⎝⎜

⎞⎠⎟

Methodology: Calculated tilting, stretching, and diabatic contributions to the lapse rate tendency following air parcel trajectories for climatology and two events from 2010.

Climatology: 72-h backward air parcel trajectories calculated from 2.5° NCEP−NCAR reanalysis

2010 events:72-h to 96-h backward air parcel trajectories calculated using 0.5° NCEP−GFS

Note:Diabatic heating approximated from Lagrangian potential temperature tendency


Trajectory ending at 600 hPa

−24 h

−48 h

−72 h

Daily-averaged Trajectory Hours

• Stretching generally balances diabatic; tilting is weak• Enhanced stretching via low-level subsidence during −24-to-0 h period• Integrated tendency approximately zero

− HLRs over Northeast U.S. primarily result from advection


700−500-hPa Lagrangian tendency for air parcels ending at 600 hPa:

Lagrangian HLR tendency following air parcels ending at 600 hPa

TiltingStretchingDiabaticTendency

Lag

ran

gia

n T

end

ency

(K

200

hP

a−1

24 h

−1 )

A B

C

0 hA B C

Objectives


• Discuss EMLs over the Northeast during:– Record high temperatures on 7 April and 26

May 2010– A severe MCS over western New England on

26−27 May 2010

7 April 2010 – Early-season warmth

ALB: 12Z/7 April

OKX: 00Z/8 April

BDL: 33.9°C (93°F)LGA: 32.8°C (91°F)POU: 32.2°C (90°F)BOS: 32.2°C DCA: 32.2°C PHL: 31.7°C (89°F)ALB: 30.5°C (87°F)CON: 30.5°C

30°C

EML

source: University of Wyoming


SBML

EML

SBML


4−7 April 2010: Potential temperature lapse rate1200 UTC 4 April − 1200 UTC 7 April 2010Minimum 700−500-hPa θ Lapse Rate [K (100 hPa)−1]Time-mean 700−500-hPa Geo. Height [dam]

72-h backward trajectoryEnding at 600 hPaEnding at 12Z/7 April 2010

H

• Air parcel trajectories are similar to climatology• Relatively low-amplitude flow pattern likely favored strong lapse rate advection off

Mexican Plateau

0.0 0.5 1.0 1.5 2.0 2.5 K (100 hPa)−1

−24 h

−48 h

−72 h

source: 0.5-degree NCEP-GFSsource: 0.5-degree NCEP-GFS

0 h

−24 h

−48 h

−72 h






Lag

ran

gia

n T

end

ency

(K

200

hP

a−1

24 h

−1 )

A

B

C

0 h A B C

4−7 April 2010: Lagrangian perspective

• Diabatic contribution via sensible heating over Mexico• Diabatic contribution via sensible heating over Ohio Valley and Northeast (prior to “leaf out”?)• Tilting generally balances stretching and diabatic contribution over Ohio Valley and Northeast• Integrated tendency is weakly positive

– maintenance via advection, modified by diabatic processes

26 May 2010 – Early-season warmth and severe MCS

WMW: 12Z/26 May

30°C

35°CEML


ALB: 00Z/27 Maysource: University of Wyoming

EML

SBML

BDL: 37.2°C (99°F)CON: 35.6°C (96°F)POU: 35.0°C (95°F)ALB: 34.4°C (94°F)YUL: 34.4°CBOS: 34.4°CLGA: 34.4°CBTV: 33.3°C (92°F)PWM: 32.8°C (91°F)


WMW: 12Z/26 May

EML



EML

SBML


MU CAPE: ~3600 J kg−1

SB CAPE: ~2800 J kg−1

0−6 km Shear: ~15 m s−1

T850 = 21.2°C… warmest May T850 in sounding record (1954−2010)

Previous T850 record: 20 May 1996 (20.2 °C)… BDL also 99°F (37.2°C)

WMW: 12Z/26 May

0130/27:

0300/27:

0430/27:

0600/27:

EML


source: College of DuPage


EML


SBML

−24 h

−48 h

−72 h

−96 h

source: 0.5-degree NCEP-GFS

22−26 May 2010: Potential temperature lapse rate1200 UTC 22 May − 1200 UTC 27 May 2010Minimum 750−550-hPa θ Lapse Rate [K (100 hPa)−1]Time-mean 750−550-hPa Geo. Height [dam]

96-h backward trajectoryEnding at 600 hPaEnding at 12Z/26 May 2010

H

• Air parcel trajectories differ from climatology• HLR advected off Mexican Plateau and circumnavigated Great Lakes region

anticyclone in high-amplitude flow pattern

0.0 0.5 1.0 1.5 2.0 2.5 K (100 hPa)−1

source: 0.5-degree NCEP-GFS

0 h

−24 h

−48 h

−72 h

−96 h






Lag

ran

gia

n T

end

ency

(K

200

hP

a−1

24 h

−1 )

A

B

C

0 h

A B C

22−26 May 2010: Lagrangian perspective

D

D

• Stretching via subsidence over TX, OK • Zero tendency (weak forcing) during anticyclonic loop over MO, IL, IA• Tilting via thermally indirect ageostrophic circulation over Canada• Negative trending tendency

– consistent with strong low-level ascent and initiation of deep moist convection

−24 h

−48 h

−72 h

−96 h






Lag

ran

gia

n T

end

ency

(K

200

hP

a−1

24 h

−1 )

A

B

C

0 h

A B C

22−26 May 2010: Lagrangian perspective

D

D

• Stretching via subsidence over TX, OK • Zero tendency (weak forcing) during anticyclonic loop over MO, IL, IA• Tilting via thermally indirect ageostrophic circulation over Canada• Negative trending tendency

– consistent with strong low-level ascent and initiation of deep moist convection

2315 UTC 26 May

http://locust.mmm.ucar.edu/

Broader Impact: March-April-May Statistics

source: Climate Services and Monitoring Division, NOAA/NCDC source: Climate Services and Monitoring Division, NOAA/NCDC

a) Northeast recorded their warmest Spring (MAM) in the 116-y record

b) Northeast MAM maximum temperature anomalies of +2 to +4°C

c) Albany, NY 365-d departure from long term mean of +1.5°C

Albany, NY31-d mean daily temperature anomaly (°C)

source: Climate Prediction Center / NCEP

(a)

(c)

Daily Averaged Temperatures Maximum Temperature Anomaly

March-May 2010(b)

Summary

• HLRs over the Northeast U.S. – preferentially occur March, April, and May– primarily result from advection off Mexican Plateau source

region

• 4−7 April 2010 HLR– resulted from advection off Mexican Plateau– likely maintained over Northeast via diabatic heating associated

with strong low-level sensible heating prior to “leaf-out”– contributed to deep mixing and record high temperatures

• 22−27 May 2010 HLR– resulted from circuitous advection off Mexican Plateau– maintained via stretching (subsidence) and tilting, weakened in

presence of deep moist convection over Northeast– contributed to record high temperatures and a severe MCS

The Influence of the Elevated Mixed Layer on Record High Temperatures and Severe Weather Over the...

Documents

Transcript of The Influence of the Elevated Mixed Layer on Record High Temperatures and Severe Weather Over the...