Day 1 Severe Weather Outlook

Valid 171300Z – 181200Z


Potential for organized severe thunderstorms will be minimal across
the contiguous United States today.

The synoptic-scale, upper-air pattern this period will be
progressive and fairly high-amplitude. As the deep cyclone now
centered over western New England moves slowly northeastward toward
the Gulf of St. Lawrence, a series of variably amplified shortwaves
will traverse the northwest flow across the Appalachians and help to
maintain troughing near the East Coast. Meanwhile, the upstream
ridge — now extending from eastern NM across the Dakotas — will
shift eastward across the mid/upper Mississippi Valley. To its
south, a currently cut-off, small cyclone is evident in moisture-
channel imagery over west TX between DRT-MAF. This should devolve
into an open-wave trough and move east-southeastward across the TX
coast by 12Z.

Those processes will occur as heights fall across much of the West
in association with a series of Pacific shortwave troughs. The
first of these — currently located over the inland Northwest from
central WA to central CA — will eject northeastward across the
northern Rockies. Another perturbation will dig southeastward from
offshore OR to the Sierra by 00Z, reaching portions of UT/AZ by 12Z.
Cold air aloft and marginal midlevel moisture, amidst falling
heights, will support isolated thunder across parts of the central
Intermountain region this evening and tonight. Another shortwave
trough — now located south of the Gulf of AK — will move east-
southeastward across the southern BC and WA coastlines around 06Z.
The latter feature may result in enough cooling aloft, prior to the
onset of low-level cold advection, to support relatively maximized
(but still isolated) thunder potential over parts of western WA/OR
this afternoon.

At the surface, the 11Z analysis showed a deeply occluded cyclone
centered near the MA/NH line, with occluded front arching across the
Gulf of Maine to open Atlantic waters. The associated cold front
trailed southwestward to central FL and the north-central Gulf,
becoming quasistationary over the northwestern Gulf off the middle/
lower TX and northeastern MX coasts. The front should move slowly
southward over the north-central/northeastern Gulf and FL today,
becoming quasistationary by evening near Lake Okeechobee. A few
thunderstorms are possible along and south of the front, especially
near the southeastern FL coastal sea breeze. Given the rich low-
level moisture content, 2000-2500 J/kg preconvective MLCAPE, and a
shallow but well-mixed boundary layer, isolated strong/briefly
damaging gusts cannot be ruled out in heavily water-loaded
downdrafts. However, the severe potential appears too isolated and
conditional to warrant a categorical outlook area at this time.

..Edwards.. 10/17/2019


Leave a Reply

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