Severe Storm Outlook Narrative (AC)
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000
ACUS03 KWNS 160613
SWODY3
SPC AC 160612

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0112 AM CDT Wed Aug 16 2017

Valid 181200Z - 191200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHEAST...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE MID
MO VALLEY REGION...

...SUMMARY...
Scattered thunderstorms, a few possibly severe, are expected across
portions of the Northeast. Isolated severe thunderstorms are also
expected across the mid Missouri Valley region.

...Northeast...

Large-scale forcing for ascent is expected to overspread the upper
OH Valley into NY during the day3 period as a significant short-wave
trough ejects across this region. This feature will be responsible
for generating considerable amount of convection upstream across the
OH Valley during the day2 period and scattered thunderstorms may be
ongoing at the start of the period Friday along/ahead of a frontal
zone from ON across western PA into the eastern TN Valley. This
activity will evolve within a narrow corridor of high PW values but
poor lapse rate environment. While convection will readily develop
along the front buoyancy will be quite limited with only an axis of
weak instability expected to develop from central PA into western NY
prior to frontal passage. Even so, increasing shear across this
region should prove adequate for sustaining organized convection
within a meager thermodynamic environment. Isolated damaging wind
gusts could be noted with the most organized storms.

...Mid MO Valley...

Strong short-wave trough is forecast to dig southeast across the
northern Plains into the mid MO Valley Friday as 40-50kt 500mb speed
max digs into eastern NE by late afternoon. Latest guidance suggest
strong boundary-layer heating will be noted ahead of wind shift that
will surge into western IA/eastern NE by 19/00z. It appears a zone
of focused ascent will overspread the mid MO Valley in response to
left exit region of 500mb speed max. Timing of this feature suggests
at least isolated thunderstorms will evolve within the corridor of
strongest heating ahead of the front then propagate toward northwest
MO during the late evening as northwesterly flow deepens across this
region. With 500mb temperatures expected to cool toward minus 12-14C
lapse rates should steepen considerably and large hail and damaging
winds can be expected with the most robust activity.

..Darrow.. 08/16/2017

$$


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