ACUS03 KWNS 190821
SPC AC 190820
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0220 AM CST Tue Feb 19 2019
Valid 211200Z - 221200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
The risk of severe thunderstorms appears negligible across the U.S.
Thursday through Thursday night.
Some further amplification of large-scale mid/upper troughing inland
of the Pacific coast appears possible during this period, as a
vigorous embedded short wave impulse continues digging into its
base, and gradually pivots across southern California and the
adjacent Southwestern international border area. Although not quite
yet coming in-phase with the subtropical stream, models suggest that
it may become increasingly so toward the end of the period.
Downstream, broad mid/upper ridging is forecast to continue to build
across much of the nation to the east of the Rockies, to the
north/northwest of a subtropical ridge, centered at mid-levels
east/southeast of the Bahamas. A remnant short wave impulse will
progress around the crest of the ridge, before digging across New
England and the Canadian Maritimes into the Atlantic. A developing
frontal wave, near the northern Mid Atlantic coast at 12Z Thursday,
is expected to rapidly deepen and become the primary associated
cyclone as it migrates away from the coast Thursday through Thursday
A quasi-stationary frontal zone trailing from this low, across the
Mid Atlantic and southern Appalachians through the lower Mississippi
Valley and Texas Gulf Coast at 12Z Thursday, may remain a focus for
continuing weak thunderstorm activity early Thursday. This may
persist through much of the period, as a continuing southerly return
flow of moisture off the Gulf of Mexico maintains weak
destabilization in a corridor across and above it. However, this
boundary is expected to gradually shift or redevelop northward
beneath the building upper ridge, with the corridor of highest
thunderstorm probabilities expected to become focused across
northeast Texas and the Ozark Plateau/Mid South/Tennessee Valley
region by late Thursday night.
Meanwhile, weak thunderstorm activity may also develop across parts
of the Rio Grande Valley into central Texas by Thursday night,
aided by elevated moisture return and destabilization associated
with the belt of westerlies emanating from the subtropical eastern
It also appears that the strong digging western impulse may
contribute to weak destabilization and low-topped convection capable
of producing lightning near the southern California coast, and
across parts of central Arizona, Thursday into Thursday night.