Jul 31, 2021 1300 UTC Day 1 Convective Outlook
Updated: Sat Jul 31 12:50:15 UTC 2021 (20210731 1300Z Day 1 shapefile | 20210731 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20210731 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
MARGINAL 240,945 18,474,701 Nashville, TN...Wichita, KS...St. Louis, MO...Norfolk, VA...Chesapeake, VA...
Probabilistic Tornado Graphic
20210731 1300 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 % 56,461 6,362,690 Norfolk, VA...Chesapeake, VA...Richmond, VA...Newport News, VA...Hampton, VA...
Probabilistic Damaging Wind Graphic
20210731 1300 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
5 % 240,876 18,476,021 Nashville, TN...Wichita, KS...St. Louis, MO...Norfolk, VA...Chesapeake, VA...
Probabilistic Large Hail Graphic
20210731 1300 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 % 112,221 6,136,854 Wichita, KS...Springfield, MO...Green Bay, WI...Appleton, WI...Oshkosh, WI...
   SPC AC 311250

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0750 AM CDT Sat Jul 31 2021

   Valid 311300Z - 011200Z


   Severe storms with damaging gusts will be possible today, mainly
   across a portion of central and southern Missouri into the
   south-central High Plains and western portion of the Tennessee
   Valley. Other strong storms will be possible over Wisconsin and
   vicinity, the coastal Carolinas, and southern Virginia.

   In mid/upper levels, the longstanding large-scale pattern of western
   ridge and eastern trough will continue, but with important internal
   changes.  The ridging from the northern/central Rockies to the
   Mid-South will break down somewhat -- especially on the east side. 
   By the end of the period, this will render a poorly defined, more
   north-south-aligned and elongated closed anticyclone -- with
   multiple, embedded, subtle 500-mb highs -- from the Canadian Rockies
   to north-central MX.  To the east, some trough amplification/height
   falls on the synoptic scale are expected over the Great Lakes, Ohio
   Valley and central Appalachians.  The biggest contributor to that
   will be a strong shortwave trough -- apparent in moisture-channel
   imagery over northwestern ON that should reach Lake Superior between
   00-03Z, and Lower MI by 12Z.  A weaker perturbation -- initially
   over western Lake Superior and western Upper MI but not well-
   depicted by most models -- that should move southeastward to the
   OH/WV area by 12Z. 

   The 11Z surface analysis showed a wavy frontal zone from near the
   coastal NC/VA border across northwestern SC, middle TN, to a weak
   low near MKC, then across northern KS to southeastern CO.  The front
   west of the Appalachians generally should move southward through the
   period, reaching southern MO, southern KS and northeastern NM by
   00Z.  The boundary will oscillate over the NC/southern VA region. 
   Farther north, a cold front associated with the ON shortwave trough
   -- initially analyzed over northeastern MN, northern SD and
   southeastern MT -- will move southward/southeastward to northern
   Lake Michigan, eastern WI, eastern IA and northern MO by 00Z. 

   ...South-central Plains to Ozarks/Mid-South...
   Isolated to widely scattered thunderstorms should develop this
   afternoon along and south of the front, offering isolated damaging
   wind and severe hail. 

   30-40-kt effective-shear magnitudes are expected under the
   southwestern rim of the stronger northwest to west-northwest flow
   aloft, over the southern MO, lower Ohio Valley and Mid-South areas. 
   This will support organized multicells, with potential clustering of
   convection locally fostering a strong-severe gust threat.  Somewhat
   less coverage -- but still amidst strong warm-sector heating, rich
   low-level moisture and frontal lift, will support isolated strong-
   severe gust potential westward across the southern KS/northern OK
   portion of the outlook.  Localized strong-severe gusts also will be
   possible with activity over the south-central high Plains, where
   well-mixed subcloud layers and steep low-level lapse rates are
   possible, even in the post-frontal surface northeasterlies. 
   However, weak deep-layer flow and related lack of shear will limit
   organization/duration of any severe threat over the Plains.

   ...Western Upper Great Lakes...
   Isolated to scattered thunderstorms should develop this afternoon
   along/ahead of the northern frontal zone, as well as potentially on
   lake-breeze boundaries.  Isolated development also may occur in the
   free warm sector.  The main concerns will be marginally severe hail
   and isolated damaging to severe gusts.  

   Despite thick smoke over much of the area, diurnal heating should be
   sufficient to reach near convective temperatures shown in forecast
   soundings, with aid from lift along the boundaries.  Peak MLCAPE of
   1000-1500 J/kg is possible, beneath midlevel instability that will
   be increased by DCVA preceding the approaching ON perturbation.
   Little change in direction with height is expected, limiting
   effective-shear magnitudes to around 30-35 kt in combination with a
   seasonally shallow buoyant profile.  However, favorable cloud-layer
   shear and anvil-level winds may aid in organization of some of the
   convection.  Activity should diminish in and near the eastern rim of
   the outlook area by mid/late evening. 

   ...Coastal Carolinas this afternoon/early evening...
   Widely scattered multicell thunderstorms should form initially this
   afternoon east and south of the front, near a surface trough and
   perhaps sea-breeze boundaries. The most persistent/intense
   convection may yield strong to isolated severe gusts in water-loaded
   downdrafts.  However, weak deep-layer flow and lack of substantial
   vertical shear should limit both duration and organization of any
   severe potential.  Strong overland diurnal heating will steepen
   low-level lapse rates in a regime of rich boundary-layer moisture--
   with dew points commonly in the 70s F.  This will contribute to a
   corridor of MLCAPE in the 2000-3000 J/kg range over the outlook

   ...Central/southern VA late overnight...
   Widely scattered to scattered thunderstorms may develop across
   central and southern VA the last few hours of the period.  Some of
   this activity may pose a threat for isolated severe gusts and a
   conditional/low-end tornado potential.  This also may constitute the
   earliest stage of the following convective day's severe threat
   regionally; see the SPC day-2 outlook for more details past 12Z.

   Though not directly affected by the aforementioned cyclonic-flow
   shortwaves, associated height falls and difluent flow will spread
   overhead.  Meanwhile, low-level lift will increase late tonight into
   early tomorrow morning local time, near an inverted trough and
   northward-bulging, surface frontal inflection area.  Along and south
   of the front, moisture advection will yield upper 60s to 70s F
   surface dew points, yielding weak MLCINH, as well as effective-
   inflow parcels that are surface-based or only slightly elevated. 
   Wind profiles will veer strongly with height, yielding around
   35-45-kt effective-shear magnitudes.

   ..Edwards/Leitman.. 07/31/2021