Sep 6, 2017 1630 UTC Day 1 Convective Outlook
Updated: Wed Sep 6 16:21:57 UTC 2017 (20170906 1630Z Day 1 shapefile | 20170906 1630Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170906 1630 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 26,685 3,830,988 Raleigh, NC...Fayetteville, NC...Cary, NC...Suffolk, VA...Greenville, NC...
MARGINAL 133,821 15,705,550 Boston, MA...Virginia Beach, VA...Norfolk, VA...Chesapeake, VA...Durham, NC...
Probabilistic Tornado Graphic
20170906 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
2 % 24,808 4,812,573 Raleigh, NC...Norfolk, VA...Chesapeake, VA...Newport News, VA...Hampton, VA...
Probabilistic Damaging Wind Graphic
20170906 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 % 26,733 3,831,839 Raleigh, NC...Fayetteville, NC...Cary, NC...Suffolk, VA...Greenville, NC...
5 % 134,237 15,841,436 Boston, MA...Virginia Beach, VA...Norfolk, VA...Chesapeake, VA...Durham, NC...
Probabilistic Large Hail Graphic
20170906 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
5 % 50,134 1,226,018 Reno, NV...Redding, CA...Sparks, NV...Medford, OR...Carson City, NV...
   SPC AC 061621

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1121 AM CDT Wed Sep 06 2017

   Valid 061630Z - 071200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS
   AFTERNOON/EVENING FROM SOUTHEASTERN VA TO NORTHEASTERN SC...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM
   SOUTHEASTERN NEW ENGLAND TO SOUTHEASTERN GA...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS
   AFTERNOON/EVENING FROM THE NORTHERN SIERRAS TO SOUTHERN OR...

   ...SUMMARY...
   Isolated severe thunderstorms are possible today into this evening
   from southeastern Virginia into eastern parts of the Carolinas, and
   also across portions of the northern Sierra Nevada into southern
   Oregon.

   ...Eastern NC and vicinity this afternoon...
   Surface heating and some destabilization is ongoing in cloud breaks
   from southeastern VA across eastern NC, to the east of a cold front
   crossing the Piedmont as of late morning.  The approach of an
   upstream shortwave trough (now over the TN Valley) will help focus
   ascent and support additional thunderstorm development along and
   ahead of the front by early afternoon.  Though midlevel lapse rates
   will not be steep, MLCAPE of 1000-1500 J/kg and effective bulk shear
   of 40-50 kt will favor a few organized clusters/supercells capable
   of producing damaging gusts.

   Isolated strong storms may also occur farther south into
   southeastern GA along and ahead of the cold front this afternoon. 
   However, weaker vertical shear with southward extent, fairly
   widespread clouds, and modest downdraft potential will tend to limit
   the severe-storm threat.  

   ...Northern Sierras to southern OR this afternoon/evening...
   The 12z Reno sounding revealed the potential for high-based
   thunderstorms this afternoon as surface temperatures warm, low-level
   lapse rates steepen, and convective inhibition is removed. 
   Thunderstorm development is expected along the fringes of the
   thicker cloud bands, as well as over the higher terrain, by mid-late
   afternoon along the northeastern periphery of the midlevel trough
   approaching central and northern CA.  A deep mixed boundary layer
   and deep-layer southeasterly flow/shear in excess of 30 kt will
   support organized storm clusters capable of producing isolated
   strong/damaging outflow winds, and perhaps some marginally severe
   hail.

   ..Thompson/Cook.. 09/06/2017

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