Valid 271200Z – 281200Z
…NO SEVERE THUNDERSTORM AREAS FORECAST…
While scattered thunderstorm activity may impact a few areas of the
U.S., mainly this evening into tonight, and perhaps most notably
across portions of the southern Plains, the risk for severe storms
Much of the nation remains under the general influence of split
branches of westerlies emanating from the mid-latitude Pacific.
However, stable conditions generally prevail, largely due to a cool
and/or dry low-level environment in the wake of broad troughing now
present across the Mississippi Valley through western Atlantic.
Models indicate that the troughing will begin to shift east of the
Mississippi Valley, and the mean trough axis offshore of the
Atlantic Seaboard, today through tonight. But, beneath a lingering
confluent mid-level regime, westerly to northwesterly (offshore)
low-level flow will prevail across much of the Atlantic and eastern
Gulf coasts. There appears likely to be little further development
of a frontal wave migrating across the north central and
northeastern Gulf of Mexico, and it may actually weaken as it
approaches the southern Florida Peninsula and Keys.
Upstream, it does appear that mid-level troughing which has crossed
the Sierra Nevada into the Great Basin may dig southeastward and
undergo considerable amplification east of the southern Rockies.
This may support weak to modest lower/mid-tropospheric cyclogenesis
across the southern high Plains by late tonight.
At the same time, another significant short wave trough emerging
from a strong mid-latitude Pacific jet is forecast to accelerate
toward the Pacific Northwest coast, within the crest of amplifying
larger-scale ridging across the eastern Pacific into the Rockies by
Any appreciable boundary layer destabilization ahead of the frontal
wave appears likely to remain largely confined to the southeastern
Gulf of Mexico and Florida Straits. In the presence of strong deep
layer shear, it is possible that scattered vigorous thunderstorm
development could impact at least the lower Keys vicinity around or
shortly after 28/00Z. This could be accompanied by some risk for a
potentially damaging wind gust or two around Key West. However,
given somewhat modest low-level hodographs and thermodynamic
profiles characterized by weak lapse rates, among other
uncertainties, severe probabilities still appear less than 5
Although generally weak, it appears that a narrow corridor of
low-level moisture return, in the presence of steepening lapse
rates, will become at least marginally sufficient to support
scattered thunderstorm activity by tonight. North of the Rio Grande
Valley, this is expected to be rooted above the boundary layer,
aided by large-scale ascent associated with lower/mid tropospheric
warm advection, particularly during the 28/03-09Z time frame across
southwestern and south central Oklahoma into central Texas.
A frontal band with embedded convection may spread into coastal
areas between 28/00-04Z. However, thermodynamic profiles more
conducive to convection capable of producing lightning appear likely
to be confined to beneath the mid-level cold pool (-28 to -30C at
500 mb) of the approaching troughing, which might not begin
impacting Washington and Oregon coastal areas until after 28/08-09Z.