Transcript mesoscale_presentatio

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?