Aug 4, 2017 1630 UTC Day 1 Convective Outlook
Updated: Fri Aug 4 16:24:15 UTC 2017 (20170804 1630Z Day 1 shapefile | 20170804 1630Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170804 1630 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 114,700 18,912,715 Columbus, OH...Cleveland, OH...Pittsburgh, PA...Buffalo, NY...Rochester, NY...
MARGINAL 275,873 43,490,644 Baltimore, MD...Charlotte, NC...Washington, DC...Nashville, TN...Atlanta, GA...
Probabilistic Tornado Graphic
20170804 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 % 82,787 5,863,664 Buffalo, NY...Rochester, NY...Syracuse, NY...Cheektowaga, NY...Utica, NY...
Probabilistic Damaging Wind Graphic
20170804 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 % 114,602 18,909,615 Columbus, OH...Cleveland, OH...Pittsburgh, PA...Buffalo, NY...Rochester, NY...
5 % 291,407 47,851,170 Baltimore, MD...Charlotte, NC...Denver, CO...Washington, DC...Nashville, TN...
Probabilistic Large Hail Graphic
20170804 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 % 390,819 62,451,745 Columbus, OH...Baltimore, MD...Charlotte, NC...Washington, DC...Nashville, TN...
   SPC AC 041624

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1124 AM CDT Fri Aug 04 2017

   Valid 041630Z - 051200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE LOWER
   GREAT LAKES/UPPER OHIO VALLEY AND INTO THE ADJACENT MOUNTAINS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   SLIGHT RISK...AND EXTENDING SOUTHWESTWARD INTO PORTIONS OF THE
   CENTRAL GULF COAST STATES/SOUTHERN APPALACHIANS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
   CENTRAL HIGH PLAINS VICINITY...

   ...SUMMARY...
   Scattered severe storms are expected this afternoon and evening from
   Ohio and West Virginia across Pennsylvania and New York and
   vicinity.  Isolated severe storms may also evolve this afternoon and
   evening across portions of the central High Plains and vicinity.

   ...Synopsis...
   Cyclonic flow aloft is forecast to expand across the U.S. today, to
   encompass nearly the entire country by the end of the period. 
   Within the broader cyclonic flow field, a pronounced short-wave
   trough will move east across the Great Lakes/Ohio Valley region
   through the day, and gradually impinge on the Northeast through the
   second half of the period.

   At the surface, a low is currently analyzed over the eastern upper
   Michigan vicinity, with a cold front trailing south across eastern
   lower Michigan and western Ohio, and then southwest across western
   Kentucky/western Tennessee/southern Arkansas into northern Texas. 
   As the front advances steadily eastward/southeastward, a zone of
   increasing thunderstorm activity focused along/ahead of the front is
   forecast to evolve through this afternoon and evening.

   ...The Northeast...
   A gradual increase in convective coverage/intensity is ongoing at
   this time from the Lake Erie vicinity south-southwest into eastern
   parts of Kentucky and Tennessee, near and ahead of the advancing
   surface cold front.  Additional afternoon heating -- particularly
   into New York/Pennsylvania/West Virginia just ahead of band of mid
   and high clouds preceding the surface front -- will support
   additional/gradual destabilization, and thus continued support for
   further convective increases.  Aiding the anticipated increase in
   convective intensity/organization will be a gradual strengthening of
   the flow field aloft across the warm sector, as the upper trough
   crossing the Great Lakes pivots east and acquires slight negative
   tilt.  The overall result will be a gradual increase in severe risk
   through the afternoon, with potential for hail and locally damaging
   winds.  Wind risk may continue into the evening -- particularly if
   storms can grow upscale into a few organized bands, but eventual
   diurnal stabilization of the boundary layer into the evening
   suggests the risk will gradually diminish after dark.

   ...The central High Plains area...
   Weak post-frontal southeasterly flow is indicated at this time
   across the High Plains area, on western fringes of a 1023 mb surface
   high currently centered over southeast Nebraska.  The southeast flow
   will maintain a ribbon of mid to upper 50s dewpoints across the
   central High Plains area, which combined with daytime heating will
   support development of 1000 to 1500 J/kg mixed-layer CAPE this
   afternoon.  Expect development of isolated storms over higher
   terrain to commence by mid afternoon, with a few storms intensifying
   locally -- aided by amply strong shear as a result of moderate
   mid-level northwest flow atop the low-level southeasterlies.  Along
   with local risk for hail, gusty/potentially damaging winds may occur
   locally as well, particularly if storms can grow upscale into a
   small cluster or two that shift southeast into/across
   lower-elevation areas of eastern Colorado and the Nebraska Panhandle
   into the evening hours.

   ..Goss/Dean.. 08/04/2017

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