Severe Storm Outlook Narrative (AC)
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ACUS01 KWNS 010535
SWODY1
SPC AC 010533

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1233 AM CDT Mon May 01 2017

Valid 011200Z - 021200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
INTO THE EVENING ACROSS MUCH OF THE LOWER GREAT LAKES REGION...THE
UPPER OHIO VALLEY AND THE CENTRAL APPALACHIANS INTO MID ATLANTIC
COAST....

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
ENHANCED RISK AREA...AS FAR SOUTH AT THE SOUTHERN MID ATLANTIC COAST
REGION...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK AREA...AS FAR SOUTH AS NORTHERN FLORIDA...

...SUMMARY...
Thunderstorms are expected to develop and overspread much of the
lower Great Lakes region, the upper Ohio Valley and central
Appalachians into the Mid Atlantic region today, accompanied by
potentially damaging wind gusts and the risk for a few tornadoes.

...Synopsis...
Ridging within the mid-latitude westerlies, centered off both the
Pacific and Atlantic coasts, may maintain amplitude during this
period, but troughing in between may broaden across much of the
interior U.S., as a significant embedded short wave trough continues
lifting northeastward out of the Plains/Mississippi Valley region.
This latter feature will be accompanied by a deep lower/mid
tropospheric cyclone which is forecast to track across and northeast
of the Great Lakes region by 12Z Tuesday, with an associated cold
front advancing into and across the Appalachians and much of the
Atlantic Seaboard.

As one smaller scale impulse continues pivoting around the eastern
and northeastern periphery of the mid-level cyclone, and another
digs to its west and south, models suggest that the short wave
trough will gradually transition from a negative to positive tilt
centered over the Great Lakes by the end of the period.  And the
mid-level cold core will continue to considerably lag to the west of
the warm sector of the occluding surface cyclone.  However,
substantial strengthening of deep layer wind fields appears likely
today within the warm sector, across much of the Atlantic Seaboard
by late afternoon.  This is where forcing for ascent is expected to
support considerable thunderstorm development, which will probably
be accompanied by potentially damaging wind gusts, and perhaps a few
tornadoes.

...Eastern states...
Models indicate strengthening of warm sector 850-500 mb wind fields
to 40-70+ kt during the day today, particularly across the lower
Great Lakes region, the upper Ohio Valley and the central
Appalachians into the northern Mid Atlantic Coast region.  This
should prove more than favorable for organized severe thunderstorm
development, given at least weak boundary layer destabilization, and
surface dew points in the 60s probably will contribute to this with
daytime heating, despite relatively warm and initially capping
mid-level layers.

Beneath increasingly difluent flow aloft, frontal and orographic
forcing for ascent are expected to aid initiation of thunderstorms
near/east of Lake Erie, southward along the western slopes of
central into southern Appalachians by 18-21Z.  This activity seems
likely to eventually consolidate and grow upscale into an organizing
squall line as it crosses the Allegheny mountains and plateau, and
to the lee of the Blue Ridge, by early evening.  As it does, it
probably will be accompanied by increasing potential for damaging
surface gusts, given the strength of the ambient wind fields, with
damaging straight line winds becoming the predominant severe threat.
However, supercell structures, within and perhaps ahead of the line
as it evolves, may be accompanied by a risk for tornadoes, one or
two of which could be strong.

Strong/severe storms may reach the Champlain/Hudson Valleys and Mid
Atlantic coastal areas by this evening, before weakening within a
more stable environment.

..Kerr.. 05/01/2017

$$



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