Day 1 Severe Weather Outlook

Valid 312000Z – 011200Z

…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PORTIONS
OF PENNSYLVANIA AND FAR WESTERN NEW JERSEY SOUTHWARD TO NORTHERN AND
CENTRAL NORTH CAROLINA…

…SUMMARY…
A band/line of strong to severe thunderstorms will continue
advancing steadily eastward this afternoon and evening, along and
east of the Appalachians from parts of New York to Georgia.
Scattered to widespread damaging winds and a few tornadoes are
expected.

…Discussion…
Prior meteorological/forecast reasoning laid out in prior outlooks
remains valid across the eastern U.S. at this time. An extensive,
broken line of strong to severe thunderstorms extends from western
PA south-southwestward along the Appalachians to the Florida
Panhandle, with additional organization/upscale growth to a more
continuous/solid line of storms expected over the next several
hours.

The primary adjustments to the outlook this update have been on the
western end — where the areas have been trimmed to account for the
current position of the frontal band, and on the southern end, where
southward expansion of the SLGT and MRGL risk areas across Georgia
has been implemented to account for slightly greater risk now
apparent across this region than currently anticipated.

Otherwise, expect scattered to widespread strong/damaging wind
gusts, and the potential for a few tornadoes embedded within the
broader convective band, well into the evening hours.

..Goss.. 10/31/2019

.PREV DISCUSSION… /ISSUED 1112 AM CDT Thu Oct 31 2019/

…Northeast to the Carolinas…
Have upgraded peak probabilities for both wind and tornado hazards
with an active period of severe weather anticipated later this
afternoon into the evening.

An amplifying shortwave trough now over IL will accelerate
east-northeast toward the Saint Lawrence Valley through tonight
toward PA/NY, while taking on a more neutral-to-negative tilt with
peak 500 mb wind speeds exceeding 120 kt. Strong surface
cyclogenesis is expected in advance of the amplifying trough, with a
cyclone moving from OH to far southern QC by early Friday. South of
the deepening cyclone, a strong cold front will sweep eastward
across the Appalachians this afternoon, reaching the Atlantic coast
overnight. The cold front will be the primary focus for severe
thunderstorms through this evening.

Northward advection of low-level moisture will continue with mid 60s
boundary-layer dew points up the OH Valley west of the Appalachians
and across southeast PA to coastal southern New England. Poor low to
mid-level lapse rates amid widespread clouds will hinder
destabilization with northern extent in the Northeast. Richer
low-level moisture (upper 60s to low 70s boundary-layer dew points)
and some surface heating in cloud breaks will support a confined
plume of MLCAPE between 750-1500 J/kg across parts of VA into the
Carolinas at peak heating.

Within the warm sector, vertical shear will increase in response to
the approach and deepening of the mid-level trough/surface cyclone.
Long hodographs with effective bulk shear of 50-60 kt are expected,
and there will also be enlarged low-level hodograph curvature for
numerous rotating storms amid effective SRH of 300-500 m2/s2.

Strong linear forcing for ascent along the cold front will be the
primary focus for storm development, mainly east of the Appalachians
later this afternoon/evening. The strong linear ascent will favor
upscale growth into a squall line, though strong deep-layer shear
and enough east component to storm motions should allow embedded
supercell structures to persist. The modest buoyancy and very strong
850-700 mb flow will favor damaging winds as the primary threat.
These could be potentially widespread within longer-tracked bowing
segments. At least a few tornadoes are also anticipated with
embedded supercell and mesovortex structures, particularly from
central NC to central MD.

The severe threat will diminish during the late evening to overnight
given an increasing dearth of surface-based instability with
east/northeast extent.

$$

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.