Valid 291200Z – 301200Z
…NO SEVERE THUNDERSTORM AREAS FORECAST…
The risk for severe thunderstorms appears negligible across the
U.S., today through tonight.
Models indicate that positively tilted mid-level troughing over the
eastern Pacific will undergo significant amplification across the
northeastern Pacific into British Columbia and the Pacific Northwest
during this period. As this occurs, a vigorous short wave trough,
now approaching the British Columbia coast, is forecast to turn
eastward, inland around the crest of the ridge, and become
increasing fragmented in splitting flow across and east of the
At the same time, one of several perturbations emerging from a
preceding inland advancing short wave trough, and now beginning to
dig into the U.S. Great Basin, is forecast to continue sharply
southward to the east of the ridging. As it approaches and crosses
the Southwestern international border area, it may provide support
for a developing frontal wave to the west of the Texas Big Bend by
Downstream, models indicate that large-scale mid-level ridging will
build from the lee of the southern Rockies through much of the
remainder of the southern tier of the U.S., today through tonight.
As it does, a significant short wave trough, initially crossing the
lower Mississippi Valley, is forecast to gradually lose amplitude
while accelerating across the Southeast, and east of the south
Atlantic Coast. But, it does appear that associated forcing for
ascent will remain sufficient to provide continuing support for weak
to modest surface wave development, along a frontal zone across the
northeastern Gulf of Mexico through the Atlantic waters north of the
Bahamas by 12Z Thursday.
Latest model output continues to suggest that potential for the
inland advection of weakly unstable, warm sector boundary layer air
across north central/northeast Gulf coastal areas is low. If this
air mass does advect inland, low-level and deep-layer shear will
probably be strong and supportive of organized severe convection.
However, at most, it currently seems that this may only potentially
impact southeast Louisiana coastal areas near Boothville around
11-13Z this morning, with enough uncertainties lingering to maintain
severe probabilities at less than 5 percent.
Otherwise, while there may be considerable mid to lower tropospheric
moistening ahead of the wave across the Florida Peninsula during the
day today, forecast soundings (particularly across the interior
peninsula) suggest that substantive moistening closer to the
surface may not take place until the 30/00-06Z time frame. The
extent to which this contributes to boundary-layer destabilization
(mainly across the southwestern and southeastern portions of the
peninsula) remains unclear, but the risk for severe weather
currently appears negligible.
Beneath cold mid-level (500 mb temps -24 to -28 C) air accompanying
the digging short wave trough, daytime heating and orographic
forcing may contribute to some convection capable of producing
lightning, mainly late this afternoon.