The Influence of the Elevated Mixed Layer on Record
High 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 Sciences
University at Albany, Albany, NY, USA
*Cooperative Institute for Research in Environmental Sciences
University of Colorado at Boulder, Boulder, CO, USA
NROW XII
Wednesday, 3 November 2010
Albany, NY
cordeira@atmos.albany.edu
NSF Support: ATM-0646907
Objectives
• 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 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
EMLs as High Lapse Rates over North America
Climatology of high lapse rates (HLRs):
• 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
• Intermountain-West U.S. maximum driven by sensible heating over semiarid 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):
• 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.:
•
•
Poleward and eastward displacement
of HLRs from their source region
~50% occur in March-April-May
Albany, NY Monthly HLR Frequency (N=33)
HLRs over the Northeast U.S.
Complementary Research:
•
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.
Fig. 3:
All sig. severe 1976-2006
– 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.
Fig. 8a:
3-km trajectories for EML
influenced sig. severe
HLRs over the Northeast U.S.
Albany, NY Monthly HLR Frequency (N=15)
HLRs over the Northeast U.S.:
•
•
Isolated March-April-May HLRs over
Albany, NY (1974−2007)
Created composite air parcel trajectories
from NCEP−NCAR reanalysis
Composite 72-h backward air parcel trajectories:
Ending at 500 hPa
Ending at 600 hPa
−24 h
0h
−24 h
0h
−48 h
−72 h
−48 h
Ending at 700 hPa
−72 h
0h
−24 h
−48 h
−72 h
hPa
Maintenance and destruction of HLRs
r



        d 
d 
Va 
 
g  
  
 p   p  p  dt 
dt  p 
 p 
Lagrangian tendency = Tilting + Stretching + Differential Diabatic
Maintenance and destruction of HLRs
r



        d 
d 
Va 
 
g  
  
 p   p  p  dt 
dt  p 
 p 
Lagrangian tendency = Tilting + Stretching + Differential Diabatic
Maintenance:
What processes produce HLR maintenance?
r
 Va 
        d 
d   

0;
0


g



 p   p   p  dt 
 p 
dt  p 
HLR maintained when right-hand side forcing terms are zero or balance
HLR maintenance suggests the local tendency is dominated by advection.
Maintenance and destruction of HLRs
r



        d 
d 
Va 
 
g  
  
 p   p  p  dt 
dt  p 
 p 
Lagrangian tendency = Tilting + Stretching + Differential Diabatic
Maintenance:
What processes produce HLR maintenance?
r
 Va 
        d 
d   

0;
0


g



 p   p   p  dt 
 p 
dt  p 
HLR maintained when right-hand side forcing terms are zero or balance
HLR maintenance suggests the local tendency is dominated by advection.
Dissipation:
What processes produce HLR dissipation?
r
 Va 
        d 
d   

0;

g



   0








 p   p  p  dt 
dt  p 
 p 
HLR dissipation for thermally direct circulations, strong low-level ascent, or cessation of
strong low-level sensible heating (or deep moist convection)
Maintenance and destruction of HLRs
r



        d 
d 
Va 
 
g  
  
 p   p  p  dt 
dt  p 
 p 
Lagrangian tendency = Tilting + Stretching + Differential Diabatic
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
HLRs over the Northeast U.S.
Lagrangian HLR tendency following air parcels ending at 600 hPa
0h
−24 h
−48 h
−72 h
Lagrangian Tendency
(K 200 hPa−1 24 h−1)
Trajectory ending at 600 hPa
Tilting
Stretching
Diabatic
Tendency
Daily-averaged Trajectory Hours
700−500-hPa Lagrangian tendency for air parcels ending at 600 hPa:
•
•
•
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 
Objectives
• 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
7 April 2010 – Early-season warmth
ALB:
12Z/7 April
source: University of Wyoming
EML
SBML
OKX:
00Z/8 April
source: University of Wyoming
EML
SBML
source: University of Wyoming
BDL:
LGA:
POU:
BOS:
DCA:
PHL:
ALB:
CON:
33.9°C
32.8°C
32.2°C
32.2°C
32.2°C
31.7°C
30.5°C
30.5°C
(93°F)
(91°F)
(90°F)
30°C
(89°F)
(87°F)
4−7 April 2010: Potential temperature lapse rate
1200 UTC 4 April − 1200 UTC 7 April 2010
72-h backward trajectory
Minimum 700−500-hPa θ Lapse Rate [K (100 hPa)−1]
Time-mean 700−500-hPa Geo. Height [dam]
Ending at 600 hPa
Ending at 12Z/7 April 2010
source: 0.5-degree NCEP-GFS
source: 0.5-degree NCEP-GFS
0h
−24 h
−48 h
−72 h
0.0
•
•
0.5
1.0
1.5
2.0
2.5 K (100 hPa)−1
Air parcel trajectories are similar to climatology
Relatively low-amplitude flow pattern likely favored strong lapse rate advection off
Mexican Plateau
4−7 April 2010: Lagrangian perspective
Lagrangian HLR tendency following air parcels ending at 600 hPa
Trajectory ending at 600 hPa
−24 h
−48 h
−72 h
Lagrangian Tendency
(K 200 hPa−1 24 h−1)
0h
Tilting
Stretching
Diabatic
Tendency
Daily-averaged Trajectory Hours
700−500-hPa Lagrangian tendency for air parcels ending at 600 hPa:
•
•
•
•
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
source: University of Wyoming
EML
ALB:
00Z/27 May
source: University of Wyoming
EML
SBML
BDL:
CON:
POU:
ALB:
YUL:
BOS:
LGA:
BTV:
PWM:
37.2°C
35.6°C
35.0°C
34.4°C
34.4°C
34.4°C
34.4°C
33.3°C
32.8°C
(99°F)
(96°F)
(95°F)
(94°F)
30°C
35°C
(92°F)
(91°F)
26 May 2010 – Early-season warmth and severe MCS
WMW:
12Z/26 May
source: University of Wyoming
ALB:
00Z/27 May
source: University of Wyoming
EML
ALB:
00Z/27 May
source: University of Wyoming
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)
26 May 2010 – Early-season warmth and severe MCS
WMW:
12Z/26 May
source: University of Wyoming
EML
0130/27:
0300/27:
ALB:
00Z/27 May
source: University of Wyoming
EML
0430/27:
0600/27:
SBML
source: College of DuPage
22−26 May 2010: Potential temperature lapse rate
1200 UTC 22 May − 1200 UTC 27 May 2010
96-h backward trajectory
Minimum 750−550-hPa θ Lapse Rate [K (100 hPa)−1]
Time-mean 750−550-hPa Geo. Height [dam]
Ending at 600 hPa
Ending at 12Z/26 May 2010
−24 h
source: 0.5-degree NCEP-GFS
source: 0.5-degree NCEP-GFS
−48 h
0h
−72 h
−96 h
0.0
•
•
0.5
1.0
1.5
2.0
2.5 K (100 hPa)−1
Air parcel trajectories differ from climatology
HLR advected off Mexican Plateau and circumnavigated Great Lakes region
anticyclone in high-amplitude flow pattern
22−26 May 2010: Lagrangian perspective
Lagrangian HLR tendency following air parcels ending at 600 hPa
Trajectory ending at 600 hPa
−48 h
0h
−72 h
−96 h
Lagrangian Tendency
(K 200 hPa−1 24 h−1)
−24 h
Tilting
Stretching
Diabatic
Tendency
Daily-averaged Trajectory Hours
700−500-hPa Lagrangian tendency for air parcels ending at 600 hPa:
•
•
•
•
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
22−26 May 2010: Lagrangian perspective
Lagrangian HLR tendency following air parcels ending at 600 hPa
Trajectory ending at 600 hPa
2315 UTC 26 May
−48 h
0h
−72 h
−96 h
Lagrangian Tendency
(K 200 hPa−1 24 h−1)
−24 h
Tilting
Stretching
Diabatic
Tendency
http://locust.mmm.ucar.edu/
Daily-averaged Trajectory Hours
700−500-hPa Lagrangian tendency for air parcels ending at 600 hPa:
•
•
•
•
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
Broader Impact: March-April-May Statistics
(a)
Daily Averaged Temperatures
source: Climate Services and Monitoring Division, NOAA/NCDC
(c)
Albany, NY
31-d mean daily temperature anomaly (°C)
source: Climate Prediction Center / NCEP
(b)
Maximum Temperature Anomaly
March-May 2010
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
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