Valid 081200Z – 091200Z
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE OHIO
VALLEY INTO CENTRAL NEW YORK AND PENNSYLVANIA…
Areas of hail and strong wind gusts are likely from the Ohio Valley
eastward into central New York and Pennsylvania. Isolated severe
hail is possible across parts of the High Plains.
A broad area of cyclonic flow aloft will stretch from the upper MS
Valley across the Great Lakes and the Northeast. A leading wave will
move across New England during the day, with a secondary stronger
wave moving into western NY and PA by 00Z. A cold front will
progress across Lakes Ontario and Erie by 18Z, and will trail
westward across central OH and IN. Ahead of the front, widespread
low to mid 60s F dewpoints will exist beneath cool profiles aloft
supporting strong to locally severe storms.
To the west, an upper ridge will exist over the Rockies, with
northwest flow over the Plains. A weak area of low pressure will
exist over the TX Panhandle and western OK, with a stationary front
extending eastward over northern OK or near the KS border. Ample
low-level moisture will exist over the central Plains, with easterly
winds north of the front aiding destabilization across the High
Plains late in the day.
…OH Valley into the Northeast…
An arcing line of storms is likely to develop by 18Z from western NY
into northwest PA along the cold front, with additional development
westward into OH and IN later in the afternoon. Northwest flow aloft
will have a large component perpendicular to the boundary, with
strong winds in the upper levels. This suggests the dominant storm
mode will be cellular, with large hail likely. Little low-level
shear/SRH suggests very low tornado risk, though damaging winds will
be possible as storms form during peak heating with steep boundary
layer lapse rates and 25-30 kt westerly 850 mb winds.
…Central and northern High Plains and northern Oklahoma into
Strong heating will occur beneath the upper ridge, while easterly
surface winds maintain 50s dewpoints into eastern WY and CO. This
will support afternoon development over the higher terrain, with
activity slowly moving eastward through evening. Weak low-level
winds beneath modest mid to upper flow will support a few
slow-moving cells or propagating outflows, with marginal hail or
wind will be possible.
To the east into OK and KS, convection is likely to be ongoing early
in the day north of the front from KS into western MO in a warm
advection regime. Heating will occur upstream across TX and OK,
resulting in areas of strong instability. New development is likely
during the late afternoon and evening along the east-west front,
with locally severe wind gusts or hail possible.