New Orleans, LA...Toledo, OH...Louisville, KY...Baton Rouge, LA...Montgomery, AL...
Probabilistic Damaging Wind Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
SPC AC 300541
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1241 AM CDT Sun Apr 30 2017
Valid 301200Z - 011200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TODAY AND TONIGHT
NEAR/EAST OF THE MISSISSIPPI VALLEY THROUGH PORTIONS OF THE SOUTHERN
GREAT LAKES...LOWER OHIO VALLEY AND CENTRAL GULF STATES...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS AREAS
SURROUNDING THE SLIGHT RISK...
Severe thunderstorms are possible today into tonight, from the
vicinity of the Mississippi River eastward through portions of the
the southern Great Lakes region, lower Ohio Valley and central Gulf
states. This includes a risk for storms capable of producing
tornadoes, a couple of which could be strong.
Models indicate that a belt of westerlies emanating from the
mid-latitude Pacific will remain amplified through this forecast
period, with large-scale ridging across the eastern Pacific into the
Pacific coast, and across the Atlantic Seaboard into the western
Atlantic, and large-scale troughing over much of the interior United
States. The large-scale troughing appears likely to take on an
increasing negative tilt orientation, as a significant embedded
short wave perturbation pivots northeast out of the central and
southern Plains through the Mississippi Valley by late tonight.
Substantive further deepening of a lower/mid tropospheric cyclone is
forecast as it tracks northeast of the southern Plains. At the
surface, the low may occlude early in the period across and
northeast of the lower Missouri Valley, with secondary low
development likely migrating across northeastern Missouri through
northern Illinois this afternoon and evening.
Within the potentially broad warm sector of the cyclone, models
indicate 50-70 kt southerly 850 mb will develop near/east of the
Mississippi Valley today. The core of a 100+ kt south/southwesterly
500 mb jet may lag to the west of the warm sector, but mid/upper
flow fields above the warm sector should still be more than
sufficient to support potential for organized severe storm
development, including supercells.
Uncertainties abound concerning the extent to which thermodynamic
profiles within the warm sector will become conducive to severe
weather potential. It appears that the northeastward advection of
elevated mixed layer air will become disrupted or cut-off from much
of the warm sector, and with the mid-level cold core lagging to the
west of the surface cold front, mid-level lapse rates are not
expected to become particularly steep. Furthermore, considerable
remnant pre-frontal convective development/cloud cover may be
present early in the period, and drying associated with ridging
centered off the Atlantic coast appears likely to slow boundary
layer moistening across much of the Southeast into portions of the
Ohio and Tennessee Valleys.
...Mississippi Valley to western slopes of the Appalachians...
Taking into account the preceding discussion, uncertainties seem too
large to allow for more than an outlook of a categorical slight risk
at the present time. But given the strength of the synoptic system
and associated wind fields, and at least a corridor of pre-frontal
boundary layer moisture characterized by surface dew points in the
mid 60s to near 70F, it may not be out of the question that a window
of opportunity for considerable severe weather potential could
develop this afternoon and evening. This seems mostly likely to be
focused near or just east of the Mississippi Valley, and mostly in
the wake of an initial north/south oriented band or two of
thunderstorms spreading east of the Mississippi Valley, where
guidance appears suggestive that breaks in the overcast could allow
insolation to contribute to at least pockets of mixed layer CAPE on
the order of 1000-2000 J/kg. Of particular concern is that the
environment could become conducive to at least isolated to widely
scattered long lived discrete supercell development, initially
anywhere from portions of eastern Missouri into Illinois, southward
through portions of western Kentucky and Tennessee into northern
Mississippi. In the presence of clockwise curved low-level
hodographs characterized by strong to extreme shear, some of these
could become capable of producing strong tornadoes.
It is possible thunderstorm activity could eventually consolidate
into one or two organized eastward advancing lines, into portions of
the southern Great Lakes region, and across the central Gulf states
by late this evening.
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z