Jan 23, 2018 1300 UTC Day 1 Convective Outlook
Updated: Tue Jan 23 12:38:13 UTC 2018 (20180123 1300Z Day 1 shapefile | 20180123 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180123 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
MARGINAL 32,743 8,625,007 Philadelphia, PA...Virginia Beach, VA...Norfolk, VA...Chesapeake, VA...Newport News, VA...
Probabilistic Tornado Graphic
20180123 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 % 16,443 2,575,146 Virginia Beach, VA...Norfolk, VA...Chesapeake, VA...Newport News, VA...Hampton, VA...
Probabilistic Damaging Wind Graphic
20180123 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 % 32,924 8,716,747 Philadelphia, PA...Virginia Beach, VA...Norfolk, VA...Chesapeake, VA...Newport News, VA...
Probabilistic Large Hail Graphic
20180123 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
No Risk Areas Forecast
   SPC AC 231238

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0638 AM CST Tue Jan 23 2018

   Valid 231300Z - 241200Z


   Strong thunderstorms may impact parts of the Mid Atlantic Coast
   region early today, accompanied by some risk for severe weather.

   Within a progressive upper-air pattern, the most pertinent feature
   for this forecast will be a mid/upper-level cyclone, currently
   centered near the southern terminus of Lake Michigan, with shortwave
   trough southwestward across the Mid-South region.  As an initially
   separate/northern-stream shortwave trough digs southeastward over
   the James Bay region, the Great Lakes cyclone will accelerate
   east-northeastward and devolve into a strong open-wave trough.  By
   00Z, the remnant 500-mb low should be located over easternmost areas
   of ON with trough southwestward over the central/southern
   Appalachians.  The trough should weaken and exit the Northeast
   coastline thereafter. 

   At the surface, the 11Z analysis shows an occluded surface low over
   west-central Lake Huron, and related occluded/cold front arching
   across western PA, west-central VA, northwestern SC, southern GA,
   and the east-central/south-central Gulf.  The front is forecast to
   sweep eastward today and move off most of the Atlantic coast by 00Z,
   with the possible exception of eastern New England and southern FL.

   An ongoing band of convection was evident in radar composites near
   an axis from ILM to RWI then diffusely northeastward across the
   Chesapeake Bay area.  This activity mostly has been producing no
   lightning, but with forecast/modified soundings suggesting the top
   of the buoyant layer close to the lower reaches of suitable
   mixed-phase zones, isolated/intermittent thunderstorms are possible
   the remainder of this morning as the band continues moving
   northeastward.  Deep/speed shear will remain favorable beneath
   90-100 kt 500-mb southwesterlies.  Mean flow aligned nearly parallel
   to the primary convective band indicates continued quasi-linear
   mode.  Modified 12Z WAL/MHX RAOBs and forecast soundings indicate
   instability will remain very limited, especially with northward
   extent; however, isolated damaging gusts may penetrate to the
   surface before this activity moves offshore late morning into early

   Limited diurnal destabilization should occur behind the initial
   convective band, based on cloud breaks evident in IR imagery and
   continued low-level warm advection immediately preceding the cold
   front.  However, considerable doubt exists on the development/
   coverage of any additional sustained convection in that
   northeastward-shifting corridor -- given currently observed and
   expected veering of prefrontal surface winds, and resultant negative
   effect on boundary-layer convergence near the front.

   ..Edwards.. 01/23/2018