SPC Jun 30, 2017 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1227 PM CDT Fri Jun 30 2017

Valid 011200Z - 021200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF
PENNSYLVANIA AND UPSTATE NEW YORK INTO THE MOUNTAINS OF WESTERN NEW
ENGLAND...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS
SURROUNDING AREAS OF THE NORTHEAST...SOUTHWARD ACROSS THE
APPALACHIANS REGION INTO PARTS OF THE TENNESSEE VALLEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN ROCKIES AND SOUTHERN HIGH PLAINS...

...SUMMARY...
Thunderstorms may impact much of the Appalachians region and
adjacent portions of the lower Great Lakes and Tennessee Valley
Saturday, accompanied by at least some risk for severe weather. 
Strong to severe thunderstorms are also possible across parts of the
southern Rockies and adjacent high Plains.

...Synopsis...
Split mid-latitude westerlies may remain modestly amplified within
at least one branch across the northern tier of the U.S. through
this forecast period, with large-scale troughing across and east of
the upper Mississippi Valley through the north Atlantic Seaboard,
and ridging inland the Pacific Northwest coast through the northern
Plains.  However, short wave troughing now approaching the Pacific
coast is forecast to progress inland and through the larger-scale
ridging across the northern intermountain region by late Saturday
night.  The southern portion of this feature may suppress
subtropical ridging across California into southern portions of the
Great Basin and lower Colorado Valley, but subtropical ridging
appears likely to otherwise remain prominent across much of the
remainder of the southern tier states.

In association with the larger-scale northeastern U.S. troughing,
one embedded short wave perturbation is forecast to accelerate
across and northeast of the lower Great Lakes region during the day
Saturday, contributing to further deepening of a surface cyclone
over northwestern Quebec, as a vigorous upstream impulse digs from
central/southern Manitoba into the upper Great Lakes region. 
Low-level cooling in the wake of the cyclone may reach the northern
and mid Atlantic Seaboard, the Tennessee Valley and the southern
high Plains  by 12Z Sunday, but the more significant/ deeper frontal
surge may not progress much south of the Great Lakes/upper
Mississippi Valley/northern Plains.

...Applachians region and adjacent Great Lakes/Tennessee Valley...
By 12Z Saturday, model output suggests that seasonably high moisture
content will become increasingly confined to a pre-frontal plume
slowly spreading across and east of the Atlantic Seaboard, and a
narrowing pre-frontal corridor becoming suppressed southward across
the Tennessee Valley, while stalling across parts of the lower
Mississippi Valley into the southern Plains Red River Valley. 
Mid-level lapse rates may remain modestly steep within a plume
extending east northeast of the southern Plains through the
Cumberland Plateau and southern portions of the Allegheny Plateau,
but steeper mid-level lapse rates associated with elevated mixed
layer air are generally expected to become confined to portions of
the central and southern high Plains.

Cloud cover and scattered precipitation associated with remnants of
overnight convection may inhibit or at least slow boundary layer
destabilization as it overspreads much of the region through the
day.  However, even with only seasonably modest surface heating in
the presence of generally weak lower/mid tropospheric lapse rates,
models still suggest that moderately large mixed layer CAPE of
1000-2000 J/kg could develop by late afternoon across parts of the
Tennessee Valley, southern Appalachians and adjacent piedmont
northward to the lee of the Allegheny Front, into the mountains of
western New England.  This probably will be sufficient to support
scattered strong thunderstorms, some of which may become capable of
producing at least localized strong surface gusts.  

Across portions of the central through northeast Pennsylvania, to
the lee of the Allegheny Front, into the Adirondacks,
Hudson/Champlain Valleys and mountains of western New England, it
still appears possible that a belt of 30-40 kt flow (within the
850-500 mb layer) overspreading the region during the afternoon and
evening could enhance thunderstorm development.  Given at least
pockets of modest boundary layer destabilization, it may not be out
of the question that shear could become supportive of isolated
supercells accompanied by at least some risk for a tornado or two.

...Southern Rockies and adjacent high Plains...
Thermodynamic profiles are expected to become characterized by
moderately large CAPE by late Saturday afternoon, in the presence of
steep lower/mid tropospheric lapse rates,  along and to the east of
the Sangre de Cristo Mountains and Raton Mesa area, southward
through the high Plains of eastern New Mexico.  This environment
probably will become conducive to at least some risk for severe hail
and wind gusts through Saturday evening.  Perhaps aided by a
nocturnal southerly low-level jet, forcing associated with warm
advection along a remnant outflow boundary/front across northeastern
New Mexico may contribute to storm consolidation and an upscale
growing cluster of storms before convection wanes late Saturday
night.

..Kerr.. 06/30/2017

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