Valid 281630Z – 291200Z
…NO SEVERE THUNDERSTORM AREAS FORECAST…
The risk of severe storms appears negligible through tonight.
…Mid-South to Southern Appalachians…
A shortwave impulse over the Lower MO Valley will progress
southeast, aiding in scattered shower development during the late
afternoon across the Mid-South. Despite surface dew points only in
the low to mid 30s, steep lapse rates through a combination of
boundary-layer heating and very cold 500 mb temperatures near -32 C
may support scant buoyancy (SBCAPE up to 250 J/kg). Here, convection
could become sufficiently deep and cloud tops sufficiently cold to
support mixed phase and charge separation, with a threat for
isolated thunderstorms containing small hail and gusty winds.
Farther east, shallow convection is expected during the late
afternoon across the southern Appalachians with a leading shortwave
impulse, but even less buoyancy and shallower convective depths
suggest that thunderstorm probabilities are below 10 percent.
…Coastal WA/northern OR…
An offshore shortwave trough near 48 N and 132 W will move inland
near the WA/BC border area by evening. Cooling mid-level
temperatures and steepening lapse rates in the post-frontal
environment should be sufficient for scant buoyancy near the coast,
and an associated threat for isolated lightning flashes after 03Z.