Day 1 Outlook Day 2 Outlook Day 3 Outlook Days 4-8 Outlook

Day 1 Outlook Convective Tornado
Hail Wind
Categorical Day1 2000Z Outlook
  
Images courtesy of the NWS Storm Prediction Center
 Forecast Discussion

  
000
ACUS01 KWNS 212004
SWODY1
SPC AC 212003

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0303 PM CDT Tue Aug 21 2018

Valid 212000Z - 221200Z

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

...SUMMARY...
Scattered damaging winds and possibly a tornado are expected across
the Lower Great Lakes and Central Appalachians vicinity mainly until
9 pm EDT.

...Appalachians/Mid-Atlantic...
Wind probabilities have been trimmed from the west across portions
of WV/eastern OH/western PA, to account for ongoing convective
trends. Some redevelopment remains possible along the cold front
with a threat of isolated damaging wind, but the primary severe
threat is expected to be with the convective band approaching
central PA/eastern WV/western MD. The threat for a brief tornado or
two remains along and ahead of this band, and also further southeast
into portions of MD/northern VA along an outflow boundary (where 2%
tornado probs have been extended), though the primary risk is still
expected to be damaging wind. 

...Utah/Colorado...
Minor adjustments have been made to the 5% wind probabilities across
portions of UT/CO, based on ongoing convective trends. Severe wind
gusts are expected to be the primary hazard in this region, though
at least small hail will also be possible with the strongest cores. 

...South-central High Plains...
No changes have been made to this area, see the previous discussion
below for more information.

..Dean/Dial.. 08/21/2018

.PREV DISCUSSION... /ISSUED 1135 AM CDT Tue Aug 21 2018/

...Lower Great Lakes to Central Appalachians/Mid-Atlantic States...
Cloud cover has been slow to thin early today, but modest cloud
breaks are noted at late morning across the upper Ohio Valley
roughly coincident with the upper dry slot. A shortwave trough over
the Midwest will continue to dampen as it moves east towards the
Lower Great Lakes while an upstream impulse over the
Upper Midwest accelerates east. A surface cyclone will track from
southern Lake Michigan into southern Ontario. However, convergence
along the lead cold front should remain modest as an upstream front
eventually overtakes this boundary early Wednesday.

Cloud cover and 12Z RAOB-observed weak mid-level lapse rates are
still expected to keep buoyancy modest overall, generally
characterized by MLCAPE around 1000 J/kg amidst upper 60s to lower
70s F boundary-layer dew points.

With a broad swath of 30-40 kt mid-level southwesterlies, scattered
storms should develop into organized clusters across the central
Appalachians and upper Ohio 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.

...Southern Appalachians toward the Gulf Coast...
While stronger forcing for ascent/vertical shear will be focused to
the north of the region, thinning cloud cover and a moist
environment (70s F dewpoints) will allow for pockets of moderate
destabilization this afternoon. A few downbursts capable of
localized wind damage may occur this afternoon/early evening with
the strongest storms.

...South-central High Plains...
It still appears there will be a semi-focused potential for a couple
of supercells along with a small multicell cluster with convection
that forms off the Sangre de Cristos and Raton Mesa vicinity and
moves eastward. A confined corridor of moderate buoyancy will
overlap the fringe of modest mid-level westerlies. Isolated large
hail and locally strong wind gusts will be possible late this
afternoon through early/mid-evening. The need for a small Slight
Risk upgrade will continue to be reevaluated through the afternoon.

...Parts of Utah/Colorado...
Some strong thunderstorms are ongoing this morning across the
region. A semi-strong belt of mid-level westerlies coincident with a
relatively moist air mass and diurnal heating should allow for some
additional storm intensification along with a greater areal coverage
through the afternoon. While locally heavy rainfall may be the most
common concern, a few storms could produce severe-caliber downburst
winds and possibly small hail.

$$