Analysis of Rare Northeast Flow Events

1. Analysis of Rare Northeast Flow Events By Joshua Beilman and Stephanie Acito

2. June 12th, 2007 Convective Event • Occurred in Central New York, North of Binghamton • Multiple Cells formed that produced severe weather • One cell in particular produced numerous reports of damaging winds and hail • 3 Boundaries Converging lead to the elevated convection and severe weather event

3. Synoptic Analysis of the Event • Cut off low pressure at each pressure level that were vertically stacked (Arnott 2010) • This Pressure center provided the rare northeast flow that fueled the two convective events • Weak inverted trough over New England at 500mb level, as well as high moisture being part of this feature. • Winds in target region were northerly and dew points were high

4. Height Plots for 850, 700, 500 and 300 hPa levels (Arnott 2010)

5. SPC Products 6/12/2007 (Arnott 2010) Convective Potential • Weak synoptic scale convergence, enhanced by the 500mb inverted trough • Short wave disturbance at mid levels, arrived at event location during early afternoon for ideal convection • CAPE over 1000 J/KG, with convective inhibition that wasn’t significant (Arnott 2010)

6. Evolution of Storms • Slight risk of severe storms was given for convective outlook with a severe thunderstorm watch in the morning of the 12th, only an hour previously there was no enhanced risk in the outlook • Pulse convection occurred in late afternoon hours around 20 UTC, dominant cell formed over Madison County, New York • By Early evening, approximately 22 UTC, pulse convection decreased, but the dominant cell was still maintaining its strength

7. Boundary Interactions • Three surface boundaries converged to produce the Madison County cell and help maintain its strength • Northeast-Southwest outflow boundary in Madison and Cortland Counties west of cells • Lake Breeze Boundary • Outflow Boundary east of cells from initial convection by Western New England Boundary Interactions during the peak of severe weather (Arnott 2010)

8. Result: • Pulse Convection From Lake Breeze and Initial Outflow boundary from the Western New England Storms develops initial severe weather along inverted trough. • Northeast southwest oriented outflow boundary adds more fuel and develops The dominant cell in Madison and Cortland counties. • 28 Storm Reports Total, most came from the Madison County cell. Severe Convection towards the end of progression (Arnott 2010)

9. Forecasting Problem Contributions: • Anomalous flow didn’t fit conceptual models for typical severe weather • The influence of the low level boundaries • Severe weather occurred northwest of places where severe weather watches occurred that day

10. June 13th Northeast Flow • 1600 UTC conditions nearly identical to the previous day • Widespread instability and Shear similar to June 12th • However surface conditions seemed less favorable for convection

11. June 13th Synoptic Analysis • Inverted trough moving southwest and enhanced low-level convergence left Binghamton area • Large area of cloud cover kept temperatures down(shown in photo) • Temps 15-20 degrees less • Surface high pressure inCanada moved in and shutoff convective potential in Eastern New York and New England

12. Synoptic Analysis Cont’d • Little change seen in Central New York • Temps around 80 F at 1600 UTC • At 1700 UTC an increase in NE winds near the surface dried out the air and dew points fell 10-15 degrees

13. Convective potential • Mid-level short wave disturbance moving SW through Central New York • WV imagery used • This would help forceUVM • Notice the cloud linerunning from LakeOntario to the Coastof Delaware

14. Convective Potential 2 • CAPE values reached 1000 J/Kg in much of Central NY and PA but reduced an hour later • Deep shear values in the 0-6km layer as well as 0-3km layer reached 20kts which favors multi-cell T-storms • Severe T-storm watch box issued at 1725 UTC away from Binghamton as low level drying occured

15. CAPE reduction 1700 UTC CAPE values 1600 UTC CAPE values Dark: 1000J/kg Mod: 500J/kg Light: 250J/kg

16. Convective Evolution • Convective development did occur Southwest of the Binghamton area in vicinity of inverted trough • However there were no reports of severe weather in the convection zones SPC severe weather outlook for June 13th 2007

17. So what happened? • Significantly less convective development mostly due to the rapid low-level drying in the early afternoon • This reduced the potential for severe weather as well as the strength of any storms that did occur. • The dry air aloft followed after passing of trough • Dry air reached the boundary layer and mixed • Northeast flow generally known as a very dry wind in this area due to air coming off the Adirondack Mountains

18. Just how rare are these events? • A 2007-2008 database was created using 70 hail/severe wx/tornado reports in the Binghamton area • Of the 70 reports only 2 had a flow direction between 0 and 90 degrees from North • That is 2.9% of the events • June 12th was the only NE flow case to produce multiple severe wx reports

19. Forecaster Challenges on June 13th • Similar conditions but different results • Upstream thermodynamic changes • Impact of orographic features on mesoscale conditions • Arrival of stable mP airmass

20. Questions?