NROW XII Wednesday , 3 November 2010 Albany, NY

1. 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

2. 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)

3. 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

4. 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 semi-arid elevated terrain • Maximum develops poleward from Mexico to Colorado between April and July

5. 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.: Albany, NY Monthly HLR Frequency (N=33) • Poleward and eastward displacement of HLRs from their source region • ~50% occur in March-April-May

6. 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. • 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. 3: All sig. severe 1976-2006 Fig. 8a: 3-km trajectories for EML influenced sig. severe

7. HLRs over the Northeast U.S. 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 Composite 72-h backward air parcel trajectories: Ending at 500 hPa Ending at 600 hPa 0 h −24 h 0 h −48 h −24 h −72 h −48 h Ending at 700 hPa 0 h −72 h −24 h −48 h −72 h hPa

8. Maintenance and destruction of HLRs Lagrangian tendency = Tilting + Stretching + Differential Diabatic

9. Maintenance and destruction of HLRs Lagrangian tendency = Tilting + Stretching + Differential Diabatic Maintenance: What processes produce HLR maintenance? HLR maintained when right-hand side forcing terms are zero or balance HLR maintenance suggeststhe local tendency is dominated by advection.

10. Maintenance and destruction of HLRs Lagrangian tendency = Tilting + Stretching + Differential Diabatic Maintenance: What processes produce HLR maintenance? HLR maintained when right-hand side forcing terms are zero or balance HLR maintenance suggeststhe local tendency is dominated by advection. 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)

11. Maintenance and destruction of HLRs 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

12. HLRs over the Northeast U.S. Lagrangian HLR tendency following air parcels ending at 600 hPa Trajectory ending at 600 hPa A B C 0 h −24 h C Lagrangian Tendency (K 200 hPa−1 24 h−1) −48 h B −72 h A 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 

13. 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

14. 7 April 2010 – Early-season warmth ALB: 12Z/7 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 source: University of Wyoming 30°C EML SBML OKX: 00Z/8 April source: University of Wyoming EML SBML source: University of Wyoming

15. 4−7 April 2010: Potential temperature lapse rate 1200 UTC 4 April − 1200 UTC 7 April 2010 Minimum 700−500-hPa θ Lapse Rate [K (100 hPa)−1] Time-mean 700−500-hPa Geo. Height [dam] 72-h backward trajectory Ending at 600 hPa Ending at 12Z/7 April 2010 source: 0.5-degree NCEP-GFS source: 0.5-degree NCEP-GFS 0 h −24 h −48 h H −72 h 0.5 1.0 1.5 2.0 2.5 K (100 hPa)−1 0.0 • Air parcel trajectories are similar to climatology • Relatively low-amplitude flow pattern likely favored strong lapse rate advection off Mexican Plateau

16. 4−7 April 2010: Lagrangian perspective Lagrangian HLR tendency following air parcels ending at 600 hPa Trajectory ending at 600 hPa A B C 0 h • 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 C −24 h Lagrangian Tendency (K 200 hPa−1 24 h−1) −48 h B A −72 h Tilting Stretching Diabatic Tendency Daily-averaged Trajectory Hours 700−500-hPa Lagrangian tendency for air parcels ending at 600 hPa:

17. 26 May 2010 – Early-season warmth and severe MCS WMW: 12Z/26 May 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°C BOS: 34.4°C LGA: 34.4°C BTV: 33.3°C (92°F) PWM: 32.8°C (91°F) source: University of Wyoming 30°C EML 35°C ALB: 00Z/27 May source: University of Wyoming EML SBML

18. 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 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) SBML

19. 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 0430/27: 0600/27: EML SBML source: College of DuPage

20. 22−26 May 2010: Potential temperature lapse rate 1200 UTC 22 May − 1200 UTC 27 May 2010 Minimum 750−550-hPa θ Lapse Rate [K (100 hPa)−1] Time-mean 750−550-hPa Geo. Height [dam] 96-h backward trajectory 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 H 0 h −72 h −96 h 0.5 1.0 1.5 2.0 2.5 K (100 hPa)−1 0.0 • Air parcel trajectories differ from climatology • HLR advected off Mexican Plateau and circumnavigated Great Lakes region anticyclone in high-amplitude flow pattern

21. 22−26 May 2010: Lagrangian perspective Lagrangian HLR tendency following air parcels ending at 600 hPa C D Trajectory ending at 600 hPa A B −24 h C D −48 h B Lagrangian Tendency (K 200 hPa−1 24 h−1) 0 h −72 h A −96 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. 22−26 May 2010: Lagrangian perspective Lagrangian HLR tendency following air parcels ending at 600 hPa C D Trajectory ending at 600 hPa 2315 UTC 26 May A B −24 h C D −48 h B Lagrangian Tendency (K 200 hPa−1 24 h−1) 0 h −72 h A −96 h Tilting http://locust.mmm.ucar.edu/ 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

23. Broader Impact: March-April-May Statistics Daily Averaged Temperatures (b) (a) Maximum Temperature Anomaly March-May 2010 • Northeast recorded their warmest Spring (MAM) in the 116-y record • Northeast MAM maximum temperature anomalies of +2 to +4°C • Albany, NY 365-d departure from long term mean of +1.5°C source: Climate Services and Monitoring Division, NOAA/NCDC source: Climate Services and Monitoring Division, NOAA/NCDC Albany, NY 31-d mean daily temperature anomaly (°C) (c) source: Climate Prediction Center / NCEP

24. 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