Valid 281300Z – 291200Z
…NO SEVERE THUNDERSTORM AREAS FORECAST…
…SUMMARY…
The risk of severe storms appears negligible today through tonight.
…Synopsis…
A deep midlevel trough will dominate the CONUS from the MS
Valley/Great Lakes to the Atlantic coast, while an upstream
shortwave trough moves inland over the Pacific Northwest this
evening. In general, low-level moisture and buoyancy will be quite
limited as a result of a prior frontal passage across the
central/eastern states. However, an embedded shortwave trough over
SD/NE early this morning will move southeastward to southern
MO/northern AR by this afternoon. Very cold midlevel temperatures
(near -32 C at 500 mb), in combination with afternoon surface
temperatures in the low 50s and dewpoints in the mid 30s, may prove
sufficient for surface-based CAPE up to 250 J/kg near the MO/AR
border. Here, convection could become sufficiently deep and cloud
tops sufficiently cold to support mixed phase and charge separation,
and the threat for isolated thunderstorms with small hail and gusty
(sub-severe) outflow winds. Farther east, shallow convection is
expected this afternoon across the southern Appalachians with a lead
shortwave trough, but even less buoyancy and shallower convective
depths (compared to MO/AR) suggest that lightning is unlikely.
Otherwise, a shortwave trough near 47 N and 135 W will move inland
over WA/northern OR by this evening. Cooling midlevel temperatures
and steepening lapse rates in the post-frontal environment should be
sufficient for weak buoyancy near the coast, and an associated
threat for isolated lightning flashes after 03z.
..Thompson/Jewell.. 02/28/2020
$$