SPC AC 040545
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1145 PM CST Sat Mar 03 2018
Valid 051200Z - 061200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS MONDAY AFTERNOON
AND EVENING ACROSS PARTS OF SOUTHEAST ARKANSAS...WESTERN AND CENTRAL
MISSISSIPPI...AND NORTHERN AND CENTRAL LOUISIANA INTO PARTS OF THE
UPPER TEXAS COASTAL PLAIN...
...SUMMARY...
A few strong thunderstorms are possible across parts of the lower
Mississippi Valley Monday afternoon and evening, accompanied by some
risk for locally damaging wind gusts and perhaps some hail.
...Discussion...
Models continue to indicate that there may be considerable further
weakening of the blocking mid/upper high center near Newfoundland
and Labrador during this period. However, little eastward
progression of the broad and deep closed low to its south (centered
over the western Atlantic) is forecast. The upstream cyclone is
still expected to slow, but guidance indicates that there will be
some eastward redevelopment of the lower/mid tropospheric
circulation center across the mid Missouri Valley toward the Upper
Midwest. This probably will be mostly in response to a perturbation
pivoting around its southeastern/eastern periphery.
While models indicate that further deepening of the mid-level low is
possible, the increasingly occluded associated surface low may
generally begin weaken by late Monday into Monday night. Where
low-level wind fields are forecast to remain fairly strong within
the narrowing warm sector of the low (generally shifting from
portions of the Ozark Plateau into the lower Ohio and Tennessee
Valleys), models continue to indicate little potential for
destabilization supportive of an appreciable risk for thunderstorm
development. It still appears that any appreciable boundary layer
destabilization will be confined to a narrow pre-frontal corridor to
the southwest, across the upper Texas coastal vicinity into the
lower Mississippi Valley.
...Lower Mississippi Valley...
Latest model runs appear at least somewhat more suggestive that
sharper/deeper surface troughing curving south of the occluded low
center could extend as far south as portions of the lower
Mississippi Valley by peak heating Monday. It appears that
low-level moistening along this feature (including surface dew
points in the lower/mid 60s F+) could support mixed layer CAPE in
excess of 500 J/kg, and perhaps as high as 1000 J/kg. And this
destabilization seems to offer a window of opportunity for vigorous
late afternoon into evening thunderstorm development. Despite
rather modest to weak low-level hodographs and shear, deep layer
shear beneath 30-50 kt westerly 500 mb flow probably will enhance
stronger storms, a few of which could be accompanied by a risk for
potentially damaging wind gusts and small to perhaps marginally
severe hail.
..Kerr.. 03/04/2018
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