Valid 251300Z – 261200Z
…NO THUNDERSTORM AREAS FORECAST…
Thunderstorms appear unlikely across the contiguous United States
today and tonight.
In mid/upper levels, a pattern shift is underway toward substantial
western troughing later in the Thanksgiving week. This period,
500-mb height falls are expected across much of the western CONUS
and Great Plains, while isohypses will be neutral to slightly
positive over most of the area from the Mississippi Valley eastward.
This will occur as a shortwave trough — now apparent in moisture-
channel imagery over inland portions of the Pacific Northwest —
digs southeastward, expands and intensifies. By 12Z, the resulting
synoptic-scale trough will extend from a 500-mb low over
northwestern CO southward over western NM to northwestern MX, with
associated cyclonic flow covering much of the Great Basin, Desert
Southwest, central/southern Rockies, and adjoining Great Plains.
At the surface, a cold front was analyzed across the Bahamas,
Straits of FL and northwestern Cuba, becoming diffuse over the
southwestern/south-central Gulf. Return flow of a partially
modified marine boundary layer will commence from the Gulf across
the central CONUS through the period, involving a broad sheet of
low-level warm advection and moisture transport, in response to
lee-side cyclogenesis progged over the southeast CO region. By the
end of the period, warm frontogenesis is forecast from that low
across the KS/Ok border region to central MO. A cold front should
develop today over the Great Basin and move southeastward, extending
by 12Z from the CO low across northwestern NM to central AZ.
Very isolated, brief thunder cannot be ruled out over either the
marine layer near the OR coastline, where low/middle-level lapse
rates will be steep atop the marine layer, or in the strong zone of
large-scale lift preceding the mid/upper wave over central/southern
UT. However, instability appears too meager to support an area of
general thunderstorms at this time.