Day 1 Severe Weather Outlook

Valid 221300Z – 231200Z


Thunderstorms capable of locally damaging winds, and perhaps a
tornado, are possible across parts of central and eastern North
Carolina into the Tidewater region of Virginia this afternoon into
the early evening.

…NC/southeast VA this afternoon/evening…
A deep, occluded cyclone over WI will move north-northeastward into
ON by this evening. An embedded speed max aloft will rotate around
the southeastern periphery of the closed low, from the TN/OH Valleys
to the Appalachians, while an associated surface cold front moves
eastward to the southeast Atlantic coast. Ahead of the cold front,
boundary-layer dewpoints of 68-72 F will spread northeastward from
GA/SC to NC and southeast VA across the Carolinas. This increasing
low-level moisture, in combination with daytime heating in cloud
breaks, will result in MLCAPE of 500-1000 J/kg this afternoon in the
warm sector.

The stronger forcing for ascent will pass primarily north of the
warm sector, which casts some doubt on storm coverage where buoyancy
will be greater this afternoon into NC. Where the warm sector keeps
pace with convection along the front into NC/southeast VA, there
will be some potential for damaging gusts given strengthening
midlevel flow. Otherwise, deep-layer vertical shear will support a
threat for supercells, though rapidly diminishing hodograph
curvature within the surface warm sector this afternoon will lead to
primarily straight hodographs and the potential for isolated
splitting storms. An isolated tornado cannot be ruled out, though
damaging gusts will be the main threat with any storms persisting
into this evening. Poor lapse rates aloft should temper any hail

…Northeast FL to SC this afternoon…
The warm sector is spreading northward this morning from GA into SC,
with low-mid 70s boundary-layer dewpoints from southeast GA into FL.
Moderate buoyancy (MLCAPE of 1000-1500 J/kg) is expected ahead of
the cold front, though deep-layer vertical shear will weaken with
southward extent. Isolated strong outflow gusts may occur with the
strongest storms along or ahead of the front this afternoon.

…Central MT this afternoon/evening…
A midlevel shortwave trough over southern BC will crest the midlevel
ridge and begin to dig southeastward over MT later this
afternoon/evening. Though low-level moisture is limited, cooling
midlevel temperatures and steepening low-midlevel lapse rates will
support at least weak surface-based buoyancy this afternoon across
central MT. Given strong wind profiles, the weak buoyancy and steep
low-level lapse rates could allow some downward momentum transfer
with low-topped convection.

..Thompson/Smith.. 10/22/2019


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