Jun 21, 2017 1630 UTC Day 1 Convective Outlook
Updated: Wed Jun 21 16:33:13 UTC 2017 (20170621 1630Z Day 1 shapefile | 20170621 1630Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170621 1630 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 291,448 19,784,067 Milwaukee, WI...New Orleans, LA...Omaha, NE...Minneapolis, MN...St. Paul, MN...
MARGINAL 360,341 54,871,217 New York, NY...Chicago, IL...Philadelphia, PA...Baltimore, MD...Pittsburgh, PA...
Probabilistic Tornado Graphic
20170621 1630 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 % 44,844 5,139,944 New Orleans, LA...Baton Rouge, LA...Mobile, AL...Metairie, LA...Lafayette, LA...
2 % 161,942 7,365,088 Des Moines, IA...Jackson, MS...Sioux Falls, SD...Cedar Rapids, IA...Rochester, MN...
Probabilistic Damaging Wind Graphic
20170621 1630 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 % 167,647 4,355,323 Omaha, NE...Lincoln, NE...Sioux Falls, SD...Fargo, ND...Sioux City, IA...
5 % 305,704 54,243,975 New York, NY...Philadelphia, PA...Milwaukee, WI...Minneapolis, MN...Pittsburgh, PA...
Probabilistic Large Hail Graphic
20170621 1630 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
SIG SEVERE 40,167 1,069,795 Sioux Falls, SD...Sioux City, IA...Grand Island, NE...Kearney, NE...Norfolk, NE...
15 % 246,501 14,587,114 Milwaukee, WI...Omaha, NE...Minneapolis, MN...St. Paul, MN...Lincoln, NE...
5 % 239,930 10,407,564 Chicago, IL...Grand Rapids, MI...Amarillo, TX...Rockford, IL...Naperville, IL...
   SPC AC 211633

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1133 AM CDT Wed Jun 21 2017

   Valid 211630Z - 221200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
   PLAINS INTO THE UPPER MIDWEST...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER THE CENTRAL
   GULF COAST REGION...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
   SOUTHERN HIGH PLAINS INTO THE NORTHERN PLAINS AND UPPER MIDWEST...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE GULF
   COAST/LOWER MISSISSIPPI VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE OHIO
   VALLEY INTO SOUTHERN NEW ENGLAND...

   ...SUMMARY...
   Severe thunderstorms are possible from parts of the southern High
   Plains to the north-central states this afternoon into tonight, with
   the greatest severe thunderstorm potential from parts of the Texas
   and Oklahoma Panhandles northeastward to Minnesota and Wisconsin. 
   Also, a risk for a few tornadoes will exist in portions of the
   north-central Gulf Coast region.

   ...Central Plains into the Upper Midwest...
   Moisture over the central Plains is expected to spread northward
   into tonight as a south-southwest low-level jet into the middle
   Missouri Valley persists this afternoon and strengthens this evening
   into the upper Mississippi Valley.  Stronger westerly winds aloft
   are located over the northern Plains and Upper Midwest, with water
   vapor imagery indicating embedded perturbations within the flow.  

   Although dynamic forcing for large-scale ascent is relatively weak,
   strong diabatic heating within the moist axis and weak low-level
   convergence along a surface trough from Nebraska into western Kansas
   will promote development of thunderstorms by mid-late afternoon over
   parts of the central Plains. Steep lapse rates within a deep
   well-mixed PBL and moderate instability with MLCAPE of 2500-4000
   J/kg will support vigorous updrafts.  Although winds aloft diminish
   with southward extent, strong directional shear with height
   indicates potential for severe storms capable of producing large
   hail and damaging wind gusts during the late afternoon and evening.

   Farther north into southeast South Dakota/southwest
   Minnesota/northwest Iowa area, there is increased uncertainty about
   storm development during the late afternoon/evening over this area,
   as some model guidance maintain a cap during peak heating in the
   wake of morning convection.  However, convergence associated with a
   surface low and an associated warm front and an approaching cold
   front/trough line suggest some potential for storm development. 
   Given large CAPE values over this region and sufficient deep layer
   shear for organized storms, a conditional severe risk will be
   maintained over this region. 

   Guidance is more supportive of storms developing along a cold front
   moving into northwest Minnesota and northeast South Dakota and
   spreading eastward during the evening hours.  Strong vertical shear 
   will support a few severe storms.  This activity is expected to
   spread eastward and develop southeastward as a strengthening warm
   advection pattern develops from Minnesota into Wisconsin during the
   overnight hours.

   ...Central Gulf Coast Area...
   As Tropical Storm Cindy moves northward toward the Sabine River
   area, zones of low-topped thunderstorms are expected to move onshore
   into tonight.  Low-level shear/SRH is sufficient to promote updraft
   rotation in some storms with a continuing potential for a few brief
   tornadoes.

   ...Upper Ohio Valley to southern New England...
   Widely scattered thunderstorms should move generally eastward across
   this corridor from midday through afternoon, offering isolated
   damaging gusts.  Diabatic surface heating, in the presence of
   surface dew points generally mid 50s to near 60 F, will steepen
   boundary-layer and deep-layer lapse rates, while weakening MLCINH
   and boosting MLCAPE to 300-800 J/kg.  Nearly unidirectional
   deep-layer wind profiles, strong speed shear and elongated
   hodographs indicate the potential for a few organized thunderstorms
   with peak gusts near severe limits and capable of tree damage.  This
   threat should diminish markedly after dark as the boundary layer
   cools.

   ..Weiss/Gleason.. 06/21/2017

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z