Valid 251200Z – 261200Z
…NO SEVERE THUNDERSTORM AREAS FORECAST…
The risk of severe thunderstorms appears negligible across the U.S.,
today through tonight.
Much of the nation will remain under the general influence of split
branches of westerlies emanating from the mid-latitude Pacific.
Amplified troughing which has developed within one branch, across
and east of the Mississippi Valley, may gradually broaden, while a
significant embedded closed low shifts east-northeastward through
the Ohio Valley and lower Great Lakes region. Upstream, a number of
smaller-scale perturbations are forecast to dig southeastward across
the Plains, downstream of short wave ridging building across the
Intermountain West and Rockies, ahead of significant troughing which
is forecast to progress into the Pacific coast by 12Z Sunday.
In association with the Ohio Valley closed low, there may be some
further deepening of the modest primary surface cyclone, migrating
across the Great Lakes into southeastern Ontario, and the secondary
low, migrating from the lee of the central Appalachians through
southern New England. A cold front trailing the secondary low
appears likely to advance east of the middle into southern Atlantic
Coast early today. It might not reach southeast Florida coastal
areas and the Keys until late tonight, but it is expected to advance
through the peninsula with negligible risk for thunderstorms,
largely due to weak low-level convergence and instability.
The trailing flank of the front may retreat northeastward across the
northwestern Gulf of Mexico and Texas Gulf coast, ahead of one of
the digging short waves and associated surface troughing progressing
through the southern Plains. In advance of the latter features, and
troughing digging within another branch, across the Mexican Plateau,
there may be weak to modest moisture return across the western Gulf
of Mexico and lower Rio Grande Valley into the southern Plains. It
appears that this may be accompanied by weak destabilization,
eventually supportive of widely scattered thunderstorm activity
(rooted above the boundary layer) late this evening into the
overnight hours. However, based on the thermodynamic profile
evolution evident in model forecast soundings, there appears
negligible risk for severe weather.