Valid 061300Z – 071200Z
…NO SEVERE THUNDERSTORM AREAS FORECAST…
Severe thunderstorms are not forecast across the contiguous United
States through tonight.
Some synoptic evolution is expected to the upper-air pattern through
the period, which initially exhibits split-flow characteristics
across the northeastern Pacific. That is largely related to a
strong cyclone centered near 39N136W, and forecast to fill slowly as
it moves east-northeastward toward the middle of the West Coast.
The 500-mb low still should be over open Pacific waters by 12Z.
However, a precursory frontal precip band, followed by cooling air
aloft (and steepening low/middle-level lapse rates), should
contribute to inland-spreading general thunder potential overnight.
Downstream synoptic ridging will cross the Rockies and deamplify
through the period, as overall CONUS flow trends more zonally in
mid/upper levels. Further contributing to that evolution, a strong
shortwave trough — now apparent in moisture-channel imagery from
central MO across eastern OK to north-central TX — will deamplify
gradually as it moves rapidly east-southeastward to GA/SC by 00Z,
then offshore. A surface low — analyzed at 11Z near TXK — will
move/redevelop southeastward across southern LA to the Gulf offshore
from the western FL Panhandle, along a cold front that should cover
about the northwestern 1/2 of the Gulf by the end of the period.
A narrow plume of favorable low-level moisture should advect across
the general-thunder area ahead of the front, and atop a relatively
stable boundary layer. Forecast soundings suggest peak elevated
MUCAPE could reach 500-800 J/kg across portions of MS/AL, with
buoyancy rooted near 850 mb, before the speedy upper wave outruns
the supportive low-level warm-advection regime. Associated widely
scattered thunderstorms already are underway across parts of AR and
northwestern MS. This activity should shift southeastward over the
general-thunder area today, with diminishing coverage late this
afternoon and evening over eastern parts of the outlook as
deep-layer forcing weakens.