U.S. EAST COAST WINTER STORM VARIABILITY DUE TO NAO AND OTHER LOW-FREQUENCY OSCILLATIONS

1. U.S. EAST COAST WINTER STORM VARIABILITY DUE TO NAO AND OTHER LOW-FREQUENCY OSCILLATIONS By Brandon MeitzMay 16th, 2011

2. U.S. EAST COAST WINTER STORM VARIABILITY DUE TO NAO AND OTHER LOW-FREQUENCY OSCILLATIONS By Brandon MeitzMay 16th, 2011 Outline What is winter storm variability? What are ECWS? What is the NAO? How does ENSO affect ECWS? PNA and ECWS Atlantic SST’s and storm tracking Concluding remarks L

3. Winter storm variability The modification of large scale atmospheric circulations that influence storm system properties in the Northeastern United States every winter. • Trough axis location variability • This affects storm tracks as well as the number of storms experienced • Eastward shift typical of Mid-Atlantic snow anomalies • Trough intensity variability • This affects intensity of storms and temperature advection that can occur along the Northeastern U.S. • Deepening of trough indicative of below average temps for Northeast U.S. Winter Storm Variability

4. East Coast Winter Storms: Mid-latitude cyclones of extra tropical origin that can form during December-March off the Atlantic Coastline of the Eastern United States as well as inland locations. Their distribution and tracking patterns are dependent on large scale atmospheric circulation. Example: Nor’easters Strong steady winds blowing out of the northeasterly direction Storms are accompanied with rain, snow, high energy waves, and storm surge Winds can exceed hurricane force L What are ECWS?

5. Redistribution of atmospheric mass along dipole Icelandic Low and Azores High • Positive phase (+) associated with relatively zonal flow across eastern U.S. • Negative phase (-) associated with meridional displacement of polar front • Variability of large scale circulation also affects SST distribution • Negative (-) NAO conditions allow encroachment of Labrador current, and southward shift of Gulf Stream • Storm tracks tend to follow Gulf Stream out to sea, missing New England What is the Northern Atlantic Oscillation?

6. Redistribution of atmospheric mass along dipole Icelandic Low and Azores High • Positive phase (+) associated with relatively zonal flow across eastern U.S. • Negative phase (-) associated with meridional displacement of polar front • Variability of large scale circulation also affects SST distribution • Negative (-) NAO conditions allow encroachment of Labrador current, and southward shift of Gulf Stream • Storm tracks tend to follow Gulf Stream out to sea, missing New England What is the Northern Atlantic Oscillation?

7. El Nino/La Nina-Southern Oscillation • The anomalous warming and cooling of equatorial Pacific Ocean temps has a teleconnection with the Atlantic Winter Storm season • During El Nino phases, cyclogenesis increases in the Gulf of Mexico/Eastern Seaboard, and decreases across Canadian Shield • La Nina phases lead to fewer coastal storms and more continental storms that affect inland New England locations • Global teleconnections of ENSO • Increased precipitation and warmer temps are experienced across Northeast as a result of El Nino phase. How does ENSO affect ECWS?

8. Why was 2009-2010 so active?

9. Overlaid NAO index (black) over PNA index • When phases opposite of each other, amplificationof meridional flow occurs • In phase index values are of opposite flow regimes (dampening) • Pacific/North American Oscillation • Positive PNA has same meridional affects to large scale flow as the negative NAO phase • PNA could act to amplify or dampen effects of NAO and other oscillations that govern East Coast Storms PNA and ECWS

10. Atlantic SST’s and storm tracking • Atmospheric Oscillations tend to influence SST’s • Meridional flows displace warm Gulf Stream Currents southwards • Zonal patterns allow northern encroachment of warm Gulf Stream currents • Atmo-Ocean-Atmo feedback seems to occur • If Gulf Stream is displaced southwards and diverts away from continent, storms also tend to veer away from land. • Wind stress is greater during positive NAO • Zonal winds stronger than meridional meandering during negative NAO phase Atlantic SST’s and storm tracking

11. Winter climate variables are many… • Trough axis and intensity off East Coast is responsible for source and intensity of storms that affect the Mid-Atlantic and Northeastern United States. • Zonal conditions lead to warmer weather across Northeast and Mid-Atlantic with Alberta Clipper systems passing through region via Great Lakes. • Meridional dip of polar front leads to cold air breakouts in Mid-Atlantic with increases in precipitation and snowfall, whereas New England can experience drought conditions. • NAO, ENSO, PNA oscillations modify large scale circulation of region leading to either zonal or meridional flow patterns. • Ocean-Atmosphere influences are still under investigation, however, with a warming climate, changes in weather patterns can be suspected to occur Concluding remarks

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