- Day Three
acus03 kwns 170817
Storm Prediction Center ac 170816
Day 3 convective outlook
National Weather Service Storm Prediction Center Norman OK
0216 am CST sun Feb 17 2019
Valid 191200z - 201200z
..there is a marginal risk of severe thunderstorms late Tuesday
through Tuesday night in a corridor across south central through
northeast Louisiana...southwest and west central Mississippi...and
adjacent portions of southeast Arkansas...
Strong thunderstorms may impact parts of the lower Mississippi
Valley late Tuesday through Tuesday night, accompanied by at least
some risk for severe weather.
As another strong short wave impulse digs off the British Columbia
coast, toward the U.S. Pacific northwest, models indicate that a
fairly significant downstream impulse will emerge from the
persistent larger-scale western U.S. Upper troughing during this
period. It appears that strongest associated mid-level height falls
will spread from the southwestern international border area, near El
Paso, Texas early Tuesday, through the middle Missouri Valley by 12z
Wednesday, as the northwestern periphery of subtropical ridging
(centered east of the bahamas) maintains considerable strength.
On this track, strongest mid-level forcing for ascent and cooling
will remain focused well to the cool side of a quasi-stationary
frontal zone near the northwest Gulf Coast. However, warming and
moistening associated with a strengthening southerly return flow off
the western Gulf of Mexico, above the surface front, appears likely
to contribute to considerable erosion of the southwestern flank of
the initially expansive cold surface ridging centered across the
upper Midwest into lower Great Lakes.
Models continue to indicate the gradual development of weak surface
troughing along the strengthening low-level jet axis (including
50-70 kt at 850 mb), across the lower Mississippi Valley toward the
lower Ohio Valley by late Tuesday night. Across parts of Louisiana
and Mississippi, this corridor may become a focus for weak
boundary-layer destabilization by Tuesday evening, as surface dew
points begin to increase through the lower/mid 60s f. Although this
probably will take place in the wake of the strongest 850 mb flow
(forecast to shift into the lower Ohio valley), lower to
mid-tropospheric wind fields may remain sufficiently strong and
sheared to contribute to an environment at least marginally
conducive to organized severe thunderstorm development.
The evolution of a narrow squall line appears possible Tuesday
night, with isolated supercells perhaps also possible within and
just ahead of the line, accompanied by at least some risk for a
tornado or two, in addition to potentially damaging wind gusts.