Analysis of Rare Northeast Flow Events By Joshua Beilman and Stephanie Acito 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 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 Height Plots for 850, 700, 500 and 300 hPa levels (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) SPC Products 6/12/2007 (Arnott 2010) 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 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) 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) 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 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 June 13th Synoptic Analysis Inverted trough moving southwest and enhanced lowlevel convergence left Binghamton area Large area of cloud cover kept temperatures down(shown in photo) Temps 15-20 degrees less Surface high pressure in Canada moved in and shut off convective potential in Eastern New York and New England 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 Convective potential Mid-level short wave disturbance moving SW through Central New York WV imagery used This would help force UVM Notice the cloud line running from Lake Ontario to the Coast of Delaware 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 CAPE reduction 1600 UTC CAPE values 1700 UTC CAPE values Dark: 1000J/kg Mod: 500J/kg Light: 250J/kg 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 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 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 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 Questions?