Analysis of Rare Northeast Flow Events

By Joshua Beilman and Stephanie Acito

June 12th, 2007 Convective EventOccurred 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 PotentialWeak 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 InteractionsThree surface boundaries converged to produce the Madison County cell and help maintain its strengthNortheast-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 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 in

Canada moved in and shutoff convective potential in Eastern New York and New England

Synoptic Analysis Cont’dLittle change seen in Central New YorkTemps around 80 F at 1600 UTCAt 1700 UTC an increase in NE winds near the

surface dried out the air and dew points fell 10-15 degrees

Convective potentialMid-level short wave disturbance moving SW

through Central New YorkWV imagery usedThis would help force

UVMNotice the cloud line

running from LakeOntario to the Coastof Delaware

Convective Potential 2CAPE values reached 1000 J/Kg in much of Central NY

and PA but reduced an hour laterDeep shear values in the 0-6km layer as well as 0-3km

layer reached 20kts which favors multi-cell T-stormsSevere 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 EvolutionConvective development did occur Southwest of

the Binghamton area in vicinity of inverted troughHowever 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 afternoonThis 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 troughDry air reached the boundary layer and mixedNortheast 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 eventsJune 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?