Valid 161200Z – 171200Z
…NO SEVERE THUNDERSTORM AREAS FORECAST…
Widely scattered thunderstorms are expected today across much of
Texas into a part of the lower Mississippi Valley. Isolated
thunderstorms are also possible along the West Coast.
A northern-stream upper trough will move onto the West Coast today
accompanied by a cold front, while a lower-amplitude southern-stream
shortwave trough reaches the southwest U.S. tonight. Farther east, a
cold front will extend from a surface low over southern New England
through the Gulf Coast states and central TX at the start of the
period. This boundary will continue south and likely extend from the
central FL Peninsula westward through the northern Gulf and into
south TX by the end of the period.
…Texas into the lower Mississippi Valley…
Southwesterly winds aloft will persist over the southern Plains
downstream from the western U.S. troughs. Weak impulses embedded
within this regime and strengthening of a southerly low-level jet
will contribute to a broad zone of isentropic ascent, theta-e
advection and weak instability in post frontal zone. Numerous
showers with embedded widely scattered thunderstorms are likely.
Most of the storms will be elevated in post-frontal region, and
while effective shear around 40 kt could support some weak mid-level
updraft rotation with any cellular storms, the thermodynamic
environment is expected to remain too marginal for a hail threat.
A cold front will move onto Pacific Northwest coastal area during
the early morning and northern CA around mid day accompanied by a
secondary shortwave trough. Mid-level lapse rates will steepen
within the post-frontal region as the thermal trough moves inland,
and pockets of diabatic heating will contribute to further
destabilization with MLCAPE from 200-300 J/kg possible. Isolated
thunderstorms appear likely in this regime, and given steep lapse
rates with cold temperatures aloft, some small hail could accompany
some of the storms.