Valid 122000Z – 131200Z
…NO SEVERE THUNDERSTORM AREAS FORECAST…
The marginal severe potential appears to have decreased across parts
of the Washington and Oregon coast. Severe thunderstorms appear
unlikely through the remainder of the afternoon and tonight.
Widespread morning showers with occasional embedded thunderstorms
have limited diurnal heating along the WA/OR Coast so far today.
Resultant MLCAPE appears minimal across this region. Low-level winds
will continue to slowly veer to southwesterly and eventually
westerly this afternoon and evening. This will tend to reduce
low-level hodograph curvature, and the potential for storm
organization/rotation. These limiting factors suggest that the
probability of a brief/isolated tornado is now too low to maintain a
Marginal Risk across this region. Locally strong/gusty winds may
still be possible in the short term.
Thunderstorms have recently developed just off the coast of far
southeastern LA. Latest surface observations and recent short-term
guidance continue to show little potential for surface-based
thunderstorms over land along the central Gulf Coast through the
remainder of the period.
.PREV DISCUSSION… /ISSUED 0954 AM CST Thu Dec 12 2019/
IR satellite imagery shows a compact and fast-moving shortwave
trough about 150nm west of Portland, Oregon. This feature and an
associated cold front will approach the coast of WA/OR in the next
few hours. A pocket of persistent lightning activity is noted ahead
of this feature, and radar suggests that scattered showers and
thunderstorms will begin moving ashore soon. Instability parameters
are quite weak with CAPE values below 200 J/kg. Nevertheless,
orographically enhanced low-level shear profiles may be sufficient
for a brief spinup as convection moves onshore. This threat is
expected to decrease by late afternoon as the cold front passes and
low-level winds veer.