Oct 7, 2017 2000 UTC Day 1 Convective Outlook
Updated: Sat Oct 7 19:58:44 UTC 2017 (20171007 2000Z Day 1 shapefile | 20171007 2000Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20171007 2000 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 11,977 1,553,182 Mobile, AL...Pensacola, FL...Biloxi, MS...Ferry Pass, FL...Prichard, AL...
MARGINAL 168,899 30,519,633 Detroit, MI...Indianapolis, IN...Columbus, OH...Cleveland, OH...Toledo, OH...
Probabilistic Tornado Graphic
20171007 2000 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 % 11,662 1,546,328 Mobile, AL...Pensacola, FL...Biloxi, MS...Ferry Pass, FL...Prichard, AL...
2 % 89,880 18,538,808 Detroit, MI...Indianapolis, IN...Columbus, OH...Toledo, OH...Cincinnati, OH...
Probabilistic Damaging Wind Graphic
20171007 2000 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 % 143,578 29,501,108 Detroit, MI...Indianapolis, IN...Columbus, OH...Cleveland, OH...Toledo, OH...
Probabilistic Large Hail Graphic
20171007 2000 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 071958

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0258 PM CDT Sat Oct 07 2017

   Valid 072000Z - 081200Z

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

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

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE GREAT
   LAKES AND OHIO VALLEY...

   ...SUMMARY...
   A couple of tornadoes are possible across the central Gulf Coast
   States in association with hurricane Nate. A brief tornado or two
   and isolated damaging winds are possible over parts of the Ohio
   Valley and Great Lakes late afternoon and evening.

   ...Central Gulf Coast...
   Minor northward adjustment was made to the outlook area over
   southwest Alabama based on current trends.  Hurricane Nate continues
   to move rapidly northward toward the central Gulf coast, with a
   primary outer convective band arcing from southeast Louisiana into
   the Gulf of Mexico to the south of far northwest Florida.  Radar
   also shows small discrete cells north of the convective band over
   from southeast Mississippi into southern Alabama, with MRMS
   low-level rotational track data and single site radars exhibiting
   transient weak rotational couplets in a few cells.  As stronger
   low-level winds and attendant shear/SRH located to the northeast of
   the TC center spread northward, potential for a couple of tornadoes
   will continue through the overnight hours over southeast parts of
   Louisiana and Mississippi into southern Alabama and northwest
   Florida.

   ...Ohio Valley/Great Lakes...
   No change has been made to this area.  Weak lapse rates and minimal
   CAPE remain evident over the warm sector in advance of a
   precipitation band extending from eastern Wisconsin southward into
   southwest Illinois.  Radar also indicates a few smaller clusters of
   weak convection downstream from the aforementioned band over the
   lower Ohio Valley.  However, no CG lightning is detected apparent at
   this time likely reflecting insufficient CAPE in the charge
   separation region.  There remains potential for a low-topped line of
   convection to develop, most likely on the leading edge of the
   Wisconsin/Illinois convective band, which will advance eastward with
   a threat for isolated damaging wind gusts into the evening hours.  A
   brief tornado will also be possible, especially in the Ohio Valley,
   where marginally favorable low-level shear and SRH are present.

   ..Weiss.. 10/07/2017

   .PREV DISCUSSION... /ISSUED 1128 AM CDT Sat Oct 07 2017/

   ...Central Gulf Coast..
   Expanded low tornado probabilities slightly farther north per latest
   track of TC Nate.

   An influx of tropical moisture and increasing low/mid-level
   winds/shear will occur this afternoon and evening, as far north as
   parts of southern AL/MS. Transient supercell structures should
   develop to the east-northeast of the inner core of Nate with a risk
   for a couple tornadoes. 

   ...OH Valley/Great Lakes...
   Added low tornado probabilities and considered a Slight risk, but
   will defer on a possible upgrade to the 20Z update.

   A pronounced midlevel shortwave trough over the central Plains will
   accelerate east-northeast to the Lower Great Lakes through tonight.
   Surface cyclone over central IA will decay over the central Great
   Lakes, but a cold front will continue eastward. A swath of robust
   insolation is underway across parts of IL/IN/OH/Lower MI between the
   warm conveyor attendant to the front and a tropical moisture plume
   preceding hurricane Nate across KY/TN. This diabatic heating should
   compensate for poor mid-level lapse rates and yield meager buoyancy
   with MLCAPE generally below 500 J/kg. 

   Ascent along the front will support a band of low-topped convection
   late afternoon into evening across IN/Lower MI. Downward transport
   of strong low-level flow should result in isolated damaging gusts,
   but the lack of a strong surface pressure rise/fall couplet may
   mitigate a greater severe wind risk. Scattered storms should form
   within the deeper moisture plume over the OH Valley late
   afternoon/early evening. Comparatively richer boundary-layer
   moisture should aid in a couple supercells/multicell clusters
   forming with risks of a brief tornado and locally damaging winds.

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