Apr 30, 2017 0600 UTC Day 1 Convective Outlook
Updated: Sun Apr 30 05:41:47 UTC 2017 (20170430 1200Z Day 1 shapefile | 20170430 1200Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170430 1200 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 271,940 40,769,154 Chicago, IL...Indianapolis, IN...Memphis, TN...Nashville, TN...New Orleans, LA...
MARGINAL 135,760 24,149,388 Detroit, MI...Columbus, OH...Milwaukee, WI...Cleveland, OH...Cincinnati, OH...
Probabilistic Tornado Graphic
20170430 1200 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
5 % 189,304 26,286,626 Chicago, IL...Indianapolis, IN...Memphis, TN...Nashville, TN...St. Louis, MO...
2 % 80,879 14,299,588 New Orleans, LA...Toledo, OH...Louisville, KY...Baton Rouge, LA...Montgomery, AL...
Probabilistic Damaging Wind Graphic
20170430 1200 UTC Day 1 Damaging Wind Probabilities 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.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 271,613 40,649,604 Chicago, IL...Indianapolis, IN...Memphis, TN...Nashville, TN...New Orleans, LA...
5 % 135,235 24,143,492 Detroit, MI...Columbus, OH...Milwaukee, WI...Cleveland, OH...Cincinnati, OH...
Probabilistic Large Hail Graphic
20170430 1200 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 270,017 40,306,779 Chicago, IL...Indianapolis, IN...Memphis, TN...Nashville, TN...New Orleans, LA...
5 % 135,984 24,473,134 Detroit, MI...Columbus, OH...Milwaukee, WI...Cleveland, OH...Cincinnati, OH...
   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...

   ...SUMMARY...
   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.

   ...Synopsis...
   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.

   ..Kerr/Gleason.. 04/30/2017

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z