Severe Storm Outlook Narrative (AC)
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000
ACUS02 KWNS 291714
SWODY2
SPC AC 291713

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1213 PM CDT Mon May 29 2017

Valid 301200Z - 311200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS
PENNSYLVANIA AND NEW YORK...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM EASTERN
KANSAS INTO MISSOURI...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
CENTRAL OREGON AND WASHINGTON...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER SOUTHERN
LOUISIANA...

...SUMMARY...
Marginally severe thunderstorms with hail and wind will be possible
on Tuesday across parts of the Northeast and from eastern Kansas
into Missouri. Isolated severe storms with hail and wind are also
possible over Washington late Tuesday into the evening. A few strong
thunderstorms with wind gusts will also be possible across southern
Louisiana.

...Synopsis...
A large upper low will remain situated over Ontario, with broad area
of strong cyclonic flow aloft from the Mid Mississippi and Ohio
Valleys across the Northeast.  A weak surface trough will move
eastward across Pennsylvania and New York, and provide a focus for
daytime thunderstorm development. Cool temperatures aloft along with
50s to near 60 dewpoints should support at least a few severe
thunderstorms there.

To the south, high pressure will be centered over the central Gulf
Coast states, but substantial moisture will remain near the coast,
especially into Louisiana and Texas which may provide enough
instability for a few strong storms and wind gusts. Out west, an
upper ridge axis will be maintained from Idaho into the Four Corners
states, with compact shortwave trough gradually breaking down the
ridge over Washington and Oregon. With a low pressure trough
deepening during the afternoon, thunderstorms will form with at
least isolated hail and wind threat by afternoon.

Hail will be possible as well across eastern Kansas into Missouri
near a weak boundary and around the southern periphery of the upper
trough where winds aloft will remain strong.

...Pennsylvania, New York, Vermont...
Storms are expected to form by around noon across western PA and NY
along the front, and will develop and move relatively slowly
northeastward during the afternoon, possibly reaching Vermont by
evening. The primary storm mode is expected to be cellular, but
small lines may eventually form with outflow mergers. Hail is
expected to be a main threat, with strong wind gusts eventually as
well. Long hodographs along with weak but veering winds with height
in the low levels suggest a few supercells are possible. A Slight
risk cannot totally be ruled out in later outlooks, although
marginal moisture and instability along with the overall weak
surface pattern look to temper the magnitude of this event.

...Washington and Oregon...
Southerly midlevel flow will increase to around 50 kt by late
afternoon with the shortwave trough and ridge breakdown. Meanwhile,
a surface trough will deepen with daytime heating. Storms are
expected to form over central Oregon and over northwest Washington
during the afternoon, and will spread northeastward through the
evening. Forecast soundings show steep midlevel lapse rates will be
present, which when combined with daytime heating will favor strong
updrafts with both hail and wind possible.

...Eastern Kansas into western Missouri...
Heating should result in marginal instability across the area as
dewpoints slowly begin to rise, mainly due to evapotranspiration.
Good mid to upper level flow will remain, and heating will lead to
around 1000-1500 J/kg MUCAPE. Hodographs will be largely straight,
favoring some splitting cells with hail threat as storms form during
the afternoon and dwindle during the evening.

...Southern Louisiana...
A moist air mass will remain along the Gulf coast near a weak warm
front maintaining 1500-2000 J/kg MLCAPE throughout the day. Rain and
storms are likely to be ongoing across the area Tuesday morning in
association with a weak midlevel disturbance which will be exiting
the northern Gulf. Even as this wave passes by, some heating should
allow for sporadic clusters of thunderstorms to redevelop, with
localized strong wind gusts the most likely threat as wind profiles
will be weak.

..Jewell.. 05/29/2017

$$


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