Severe Storm Outlook Narrative (AC)
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000
ACUS01 KWNS 240531
SWODY1
SPC AC 240530

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1230 AM CDT Tue Oct 24 2017

Valid 241200Z - 251200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE NORTHEAST STATES...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
NORTHERN MID-ATLANTIC STATES INTO SOUTHERN NEW ENGLAND...

...SUMMARY...
A few severe thunderstorms are possible today across a portions of
the Northeast, particularly across New Jersey northward through the
Hudson Valley.  These storms will be accompanied by a risk for a few
strong to damaging wind gusts and possibly a tornado or two.

...Synopsis...
Shortwave trough currently moving through the upper OH Valley is
expected to pivot northward/northwestward through the Lower Great
Lakes region and into far eastern Ontario before maturing further
over the Upper Great Lakes. An additional shortwave trough,
currently moving into the middle MS Valley, will continue
eastward/southeastward through the TN Valley and Southeast States.
Evolution of this pair of shortwaves will result in the
amplification of the parent upper trough over much of the central
and eastern CONUS.

At the surface, low associated with the upper OH Valley shortwave
trough will further occlude and remain largely in place over the
Great Lakes as the overall cyclone matures. Attendant cold front
will gradually progress eastward across the Northeast and off the
Mid-Atlantic coast. By 00Z Wednesday, this front will likely extend
from VT southward to off the NC coast.

...Northeast...
Low-level moisture is expected to increase across the region as
southeasterly low-level flow encourages moisture advection ahead of
the approaching cold front. General expectation is for mid 60s
dewpoints to be in place by early morning across southern portions
of the Northeast (i.e. NJ and Hudson Valley ) with lower 60s
dewpoints likely extending as far north as southern VT. Despite this
favorable low-level moisture, the lack of strong forcing for ascent
and leading stratiform character to the convective line will result
in poor lapse rates, limited heating, and moist profiles, all of
which will act to limit instability. HREF suggests SBCAPE will
remain below 500 J/kg across the majority of the area. The only
exception is across NJ where higher dewpoints will likely support
slightly stronger instability.

In contrast to the marginal thermodynamic environment, strong wind
fields, particularly below 700 mb, will provide a favorable
kinematic environment for strong/severe storms. Guidance suggests
850 mb winds will be near 55 kt and 0-1 km SRH will be around
250-300 m2/s2 within the warm sector. The resulting low CAPE/high
shear environment will likely support sporadic/transient strong
updrafts capable of damaging wind gusts. Additionally, given the
strength of the low-level wind fields, a tornado or two is also
possible.

..Mosier.. 10/24/2017

$$



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