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Day 1 Outlook Convective Tornado
Hail Wind
Categorical Day1 1300Z Outlook
  
Images courtesy of the NWS Storm Prediction Center
 Forecast Discussion

  
000
ACUS01 KWNS 211241
SWODY1
SPC AC 211239

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0739 AM CDT Tue Aug 21 2018

Valid 211300Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LOWER GREAT LAKES
AND CENTRAL APPALACHIANS...

...SUMMARY...
Scattered damaging winds are possible across the Lower Great Lakes
and Central Appalachians vicinity between about 3 to 9 pm EDT.

...Lower Great Lakes to Central Appalachians/Mid-Atlantic States...
Shortwave trough over the Midwest will dampen as it moves east
towards the Lower Great Lakes while an upstream impulse over the
Upper Midwest accelerates east. This will result in deepening of the
surface cyclone as it tracks from southern Lake MI into southern
Ontario. However, convergence along the lead cold front should
remain modest as an upstream front eventually overtakes this
boundary early Wednesday.

Scattered to broken showers and storms are ongoing east-southeast of
the aforementioned cyclone and these will limit daytime
destabilization, especially across the Lower Great Lakes. Potential
for pockets of greater surface heating will exist from southwest PA
and locations south. Here, modest buoyancy characterized by MLCAPE
around 1000 J/kg is anticipated given upper 60s to lower 70s
boundary-layer dew points coincident with weak mid-level lapse rates
of 5.5-6 C/km. 

With a broad swath of 30-40 kt mid-level southwesterlies, scattered
storms should develop into organized clusters across the central
Appalachians and Upper OH Valley. A few supercells may also be
favored in the western PA/northern WV/western MD region where
stronger low-level southerlies should overlap the northern extent of
the modest buoyancy plume with a risk for isolated severe gusts and
a tornado. Otherwise, strong gusts producing scattered tree damage
should be the primary hazard, especially with southeast extent where
weaker low-level winds are expected. A tornado is also possible
farther north into western NY given modest enlargement to low-level
hodographs within the warm conveyor east of the surface cyclone.
However, prospects for appreciable surface-based destabilization
with northeastern extent appear weak and thus will not increase
tornado probabilities this outlook.

...South-central High Plains...
A rather focused signal for a supercell or two, along with a small 
multicell cluster is expected with convection that forms off the
Sangre de Cristos and Raton Mesa vicinity. A very confined corridor
of moderate buoyancy should overlap the fringe of modest mid-level
westerlies. This should offer a spatially limited risk for isolated
severe hail/wind between about 4-9 pm MDT.

..Grams/Broyles.. 08/21/2018

$$