Valid 071300z - 081200z
..there is a MDT risk of severe thunderstorms late this afternoon/evening for
NE Indiana and Northern Ohio...
..there is a slight risk of severe thunderstorms this afternoon into early
tonight from the lower Great Lakes/Ohio Valley to the lower MS
valley...
...
A midlevel trough over the northern plains this morning will progress eastward
to the Great Lakes and intensify through tonight. The midlevel
trough will be preceded by a deepening surface cyclone which will
move east-northeastward along a baroclinic zone from NE MO this morning to the
lower Great Lakes overnight. The moist warm sector will spread northeastward
in advance of the surface low...reaching northern Indiana/Ohio this
afternoon. Trailing the surface low...a cold front will move eastward
across the Ohio Valley and southeastward across the MS valley. The primary
focus for severe storm development today into early tonight will be
the surface low and cold front across the Ohio Valley.
..OH valley area later this afternoon into early tonight...
A swath of boundary layer dewpoints in the low 60s is spreading
northward/northeastward from the lower MS valley to the Ohio Valley...beneath a
remnant elevated mixed layer from the Southern Plains. Continued moisture
advection through the day and strong surface heating S of the warm
front will contribute to the development of moderate instability
/MLCAPE of 1000-1500 j per kg/ in the warm sector today across the
Ohio Valley. Convective inhibition associated with the remnant eml
will likely delay convective initiation until middle-late afternoon
near the surface low...while later storm development is expected in
the evening farther S/SW along the cold front.
Meanwhile...vertical shear will be strong within the northern portion of
the warm sector in conjunction with a 40-50 knots south-southwesterly low level jet...and 60-70
knots west-southwesterly midlevel flow with the approaching trough. The net result
will be an environment supportive of both supercells and short
bowing segments. Damaging winds will be the main severe
threat...though a few tornadoes and large hail can also be expected
given effective srh of 200-300 m2/s2 and the likelihood of a few
discrete storms late this afternoon/evening. Overnight...the severe
threat should diminish as the boundary layer stabilizes.
However...some potential for damaging winds will persist across PA
and western New York near and immediately southeast of the surface low track...in
proximity to the stronger mean flow and height falls.
..TN/lower MS valleys late this afternoon/evening...
Scattered thunderstorm development is expected by about 00z along
the southeastward-moving cold front...where low-level ascent and daytime
heating/mixing will have weakened convective inhibition. Boundary
layer dewpoints increasing into the middle-upper 60s and afternoon
temperatures of 85-90 f will result in MLCAPE values of 2000-3000
j/kg in a narrow corridor east of the cold front. Deep-layer vertical
shear will be at least marginally favorable for supercells and
persistent storm clusters for a few hours this evening...before
instability weakens. Isolated damaging winds and large hail will be
the main severe storm threats.
..interior central/S Florida this afternoon...
Local sea breeze circulations will support isolated thunderstorm
development this afternoon...primarily across the interior
central/southern peninsula with boundary collisions. Storm coverage will
be limited by the drying aloft noted in satellite precipitable water fields and 12z
soundings compared to yesterday. Still...somewhat organized storms
will be possible in the weak northwesterly flow aloft in an environment of
moderate instability. The strongest storms may produce strong
downburst winds and some hail.
.Thompson/Hurlbut.. 05/07/2010
