Day 1 Severe Weather Outlook

Valid 271300Z – 281200Z


Isolated thunderstorms may occur today across parts of the Great
Lakes, Northeast, and Mid-Atlantic, as well as portions of the
Southeast and California. Severe thunderstorms appear unlikely.

In mid-upper levels, large-scale troughing will be reinforced over
the western CONUS by a synoptic cyclone now centered over southern
OR, and covering much of the Pacific Northwest and northern CA. The
core region of this cyclone is forecast to move slowly southward
across northern CA through the period, anchoring a trough that will
extend from the Canadian Rockies to the tropical eastern Pacific by
12Z. A broad area of cold midlevel air and steep low/middle-level
lapse rates, atop at least marginally moist low levels, will support
general thunder potential over much of central and coastal CA, with
stronger cells producing small hail.

As heights fall over the Southwest ahead of this system, a formerly
cut-off low west of Baja — now in the process of rejoining the
midlatitude westerlies — will eject northeastward. This
perturbation will weaken considerably and become a low-amplitude,
open shortwave trough as it crosses Baja and the Gulf of CA this
evening. While the progged CAPE/shear parameter space and
convective fields suggest possible supercells around the southern
Gulf of CA, ahead of the ejecting perturbation, conditions should
become too stable for thunderstorms northward near the international

An occluded, nearly vertically stacked, deep-layer cyclone initially
centered over southwestern WI will move across the Great Lakes,
southern ON, and the Northeast through the period. The mid/upper
low should reach near Cape Cod by 12Z, with a new surface cyclone
forming overnight and moving eastward across NY and New England.
The associated/elevated conveyor of warm advection and moisture
transport may become sufficiently unstable to support isolated,
episodic thunderstorms, aided by frontal forcing.

The cold front was analyzed at 11Z from eastern IN across middle TN,
central/southwestern MS, southern LA, the TX coastal bend, and
westward across northern MX. The front should reach the eastern
Carolinas, southern GA, and the western FL Panhandle by 00Z, then
move offshore of the Atlantic Coast overnight, except for parts of
the FL Peninsula. Isolated to widely scattered thunderstorms are
possible along and ahead of the cold front through mid/late
afternoon from the central Gulf Coast and FL Panhandle to parts of
the southern Appalachians. With time, convective coverage and
intensity should diminish. This will occur in tandem with a
narrowing sector of favorably moist boundary-layer air, as the front
impinges on progressively lower-theta-e warm-sector trajectories
emanating from the prior frontal passage, amidst weakening of both
large-scale support and overall lift.

..Edwards.. 11/27/2019


Leave a Reply

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