Day 1 Severe Weather Outlook

Valid 222000Z – 231200Z

…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM NORTHEAST
FLORIDA THROUGH THE EASTERN CAROLINAS AND SOUTHEAST VIRGINIA AS WELL
AS OVER A PORTION OF CENTRAL AND EASTERN MONTANA…

…SUMMARY…
A few strong/severe thunderstorms with gusty winds remain possible
from northeast Florida to eastern North Carolina and southeast
Virginia this afternoon, as well as central and eastern Montana this
evening.

…Discussion…

Have adjusted the MRGL risk area eastward based on progression of
the cold front. A few instances of strong wind gusts remain possible
this afternoon as thunderstorms develop along and just ahead of the
front.

..Dial.. 10/22/2019

.PREV DISCUSSION… /ISSUED 1129 AM CDT Tue Oct 22 2019/

…North Carolina/southeast Virginia this afternoon/evening…
The potential exists for a few thunderstorms capable of locally
damaging winds, and possibly a tornado, across the region this
afternoon into early evening, although the overall magnitude/extent
of today’s severe risk should remain limited.

Associated with the base of a prominent east-central CONUS longwave
trough, a vorticity maxima and the entrance region of a strong
cyclonically curved polar jet will quickly transition
east-northeastward from the Tennessee Valley and Lower Ohio Valley
to the Appalachians by tonight. Modest cyclogenesis will occur in
the lee of the southern/central Appalachians as a cold front
continues to spread east of the mountains, and generally exits the
coast by early/mid-evening. A warm/moist sector with 70F dew points
will precede the cold front, with a north-northeastward expansion
across coastal portions of South Carolina/North Carolina today.

Even with this moist influx off the Atlantic, the relatively
small-inland warm sector remains mired by broken multi-layer cloud
cover at midday. Its potential persistence will temper lapse rates
and limited upward parcel accelerations even with near 70F surface
dewpoints, which casts uncertainty on how many mature/sustained
surface-based storms will develop and intensify within the warm
sector. That said, strengthening/gradually backing mid-level winds
and resultant 45-55 kt effective shear will be conditionally
supportive of fast-moving line segments capable of damaging winds,
with some supercell/non-zero tornado potential particularly across
eastern North Carolina in proximity to the warm front, should
adequate destabilization and storm development/maturation occur.

…Northeast Florida to South Carolina this afternoon…
A moist air mass and 80 F temperatures are contributing to moderate
destabilization (MLCAPE of 1000-1500 J/kg) early this afternoon
ahead of the east/southeast-moving cold front. Sufficient
instability exists for a potential increase in storm
coverage/intensity, although pre-frontal winds continue to veer with
weakening near-frontal convergence. Isolated strong outflow gusts
may occur with the strongest storms along or ahead of the front this
afternoon, although the overall magnitude/coverage of the risk is
likely to remain limited.

…Central Montana 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.

$$

Leave a Reply

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