By: Peter Banacos
And
Michael Ekster
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The horizontally advected hot, dry, and
deeply mixed boundary layer air over areas of
lower terrain.
Lies atop an interface of strong static
stability, creating CIN
Similar to a “loaded gun” sounding.
Late spring / summer phenomenon
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EML formation is well understood, however its
movement, evolution, and inevitable dissipation
has received less attention
Johns and Dorr (1996)
Farrell and Carlson (1989)
◦ Solely focused on tornadoes and not derechos or large
hail events
◦ Performed prior to high-powered compositing
techniques
This paper attempts to catalog significant severe
weather
◦ Hail >2 in. (5.1 cm) in diameter,
◦ Convective wind gusts >65 kt (33 m s^-1)
◦ Tornadoes of >F2 intensity
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𝜗𝛾
𝜗𝑡
=−
1 𝜗𝑄
𝐶𝑝 𝜗𝑧
− 𝐕 ∙ 𝛻ℎ 𝛾 − 𝑤
𝜗𝛾
𝜗𝑧
+
𝜗𝑽
𝜗𝑧
∙ 𝛻ℎ 𝑇 +
𝜗𝑤
𝜗𝑧
Γ𝑑 − 𝛾
A
B
C
D
E
A = Diabatic Heating Term, where a decrease
(increase) in diabatic heating with height yields a
steepening (lessening) lapse rate
B = Horizontal Lapse Rate Advection term
C = Vertical Lapse Rate Advection term
D = Differential Temperature Advection term,
where a steepening (lessening) lapse rate would
occur within a thermally indirect (direct) circulation
E = Vertical Stretching term.
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As well as differential ageostrophic
temperature advection being positive
(downstream of amplifying baroclinic wave,
jet entrance, or frontogenetic circulation)
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929 significant severe reports (3% of original
30,617 reports)
EML soundings were chosen based on:
◦ An elevated lapse rate ≥ 8°C/km through a depth of
200 hPa or greater
◦ An increase in environmental relative humidity with
height from a minimum at the bottom of the layer of
steep lapse rate, through the depth of the steep lapse
rate layer
34 significant severe weather days from 19702006 that met an “EML” criterion.
This accounted for only 0.1% of severe weather
reports in the NE, but owed to 52.9% of
fatalities and 45% of injury totals.
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Constructed composite analyses of 700 hPa
heights and temperatures,700-500 hPa lapse
rates, LI, and MSLP.
Backward Lagrangian trajectories at 250 hPa
AGL, and every km up to 6km for a duration
of 96 hours.
•700 hPa height
anomalies
•EML events have a
stronger northerly
displaced ridge and
heights anomalies
of 36 m.
•Placement of ridge
and trough allow for
a westerly
geostrophic flow.
•700 hPa temperature
anomalies
•Positive anomaly
maxima moves from
central plains to the
Northeast.
•Anomalies of +3°+3.5°C exist.
•750-500 hPa lapse rate
•The EML composite mean value
is 7.5°-8°C km
•Anomalies are +1°C/km
•Plume extends across Great
Lakes region.
•Important because EML plume
shows steeper lapse rates.
•LI and MSLP
•MSLPs are similar in EML and non-EML cases
•Illustrates importance of atmosphere aloft-EML Plume.
•Greater potential instability in the EML composite.
•Anticyclonic curvature
•Consistent with the 700 hPa
ridge
•Most originate over the
Intermountain West
•Similar paths to 700 hPa
temperature anomalies
and 750-500 hPa lapse
rate composites.
•(b) represents 10 trajectories
showing three-quarter or
greater anticyclonic loops.
Trajectory Analysis
•After t-51 h, parcel begins subsiding.
•Dp/Dt shows subsidence 1-2 prior to event followed by accent.
•Subsidence strengthens capping inversion
•Maintains EML plume by not allowing DMC.
•Vertical velocity switches sign at t-14 h.
•Rising motion allows cap to weaken and DMC fires.
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Eastern New Yorkwestern Massachusetts
tornadoes: 28 August
1973
350 km swath of
severe weather
Associated with an
EML event
Case Studies
Case Studies
Case Studies
• Northern New
England and
southern Quebec
derecho: 5 July
1999
Case Studies
Case Studies
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Hypothesize V ∙ 𝛻ℎ and ω > 0 within the EML
plume are both essential for maintenance and
transport over large distances. Release of
instability over the NE is essential.
Mean 700hPa anticyclonic flow featured over
Tennessee River valley.
700hPa trough along the West Coast that results in
ejection of the EML plume across the plains.
Anticyclonic flow across the plains, yielding mean
ω > 0 and limited convection for plume
maintenance until it moves downstream of the
ridge axis.
Shortwave trough embedded in enhanced to
moderately strong WNW mid-level flow across
Great Lakes, which leads to entrained EML air,
leading to convection and ω < 0