Aug 18, 2017 0600 UTC Day 2 Convective Outlook
Updated: Fri Aug 18 05:04:10 UTC 2017 (20170818 0600Z Day 2 shapefile | 20170818 0600Z Day 2 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170818 0600 UTC Day 2 Outlook Graphic
Day 2 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
MARGINAL 115,025 11,828,210 Columbus, OH...Cleveland, OH...Pittsburgh, PA...Akron, OH...Erie, PA...
Probabilistic Graphic
20170818 0600 UTC Day Probabilitic Graphic
Probability of severe weather within 25 miles of a point.
Hatched Area: 10% or greater probability of significant severe within 25 miles of a point.
Day 2 Prob. Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
5 % 113,594 11,657,408 Columbus, OH...Cleveland, OH...Pittsburgh, PA...Akron, OH...Erie, PA...
   SPC AC 180504

   Day 2 Convective Outlook CORR 1
   NWS Storm Prediction Center Norman OK
   1204 AM CDT Fri Aug 18 2017

   Valid 191200Z - 201200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SATURDAY
   AFTERNOON AND EVENING ACROSS PARTS OF THE UPPER OHIO VALLEY AND
   LOWER GREAT LAKES REGION...

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

   CORRECTED 5 PERCENT SEVERE LINE ACROSS OHIO VALLEY/LOWER GREAT LAKES
   REGION

   ...SUMMARY...
   Strong thunderstorms may impact parts of the upper Ohio Valley and
   lower Great Lakes region, as well as portions of the central Plains,
   on Saturday, accompanied by some risk for severe weather.

   ...Synopsis...
   The mid-latitude westerlies are in the process of retreating to the
   general vicinity of the Canadian/U.S. border area.  As this occurs,
   subtropical ridging appears likely to become a bit more prominent
   over an expanding portion of the central and southern U.S. by
   Saturday, particularly to the east of the Rockies.  Lingering upper
   troughing within the westerlies is forecast to accelerate east
   northeast of the Great Lakes/Ohio Valley region, into Quebec and the
   Northeast by late Saturday night.  Within this regime, models
   indicate that an appreciable embedded short wave impulse will pivot
   into and through the upper Ohio Valley during and shortly after the
   peak heating hours Saturday afternoon and evening.  The most
   significant upstream short wave trough is expected to mainly
   progress across Saskatchewan and Manitoba, but a minor perturbation
   trailing to the southwest of this feature may migrate across the
   northern U.S. intermountain region.

   ...Upper Ohio Valley/lower Great Lakes region...
   Although seasonably high moisture content is expected to be
   spreading east of the Atlantic Seaboard by early Saturday, guidance
   indicates that residual low-level moisture may be sufficient to
   contribute to modest boundary layer destabilization (CAPE up to
   around 1000 J/kg) by Saturday afternoon.  This is expected in
   response to insolation, beneath a relatively cool mid-level air mass
   forecast to overspread the region (500 mb temps of -12 to -14 C). 
   Aided by mid-level forcing for ascent, scattered thunderstorm
   activity is expected to initiate by early to mid afternoon, in the
   presence of modest vertical shear associated with 30-40 kt cyclonic
   mid-level flow.  At least marginally severe hail and localized
   potentially damaging wind gusts appear possible in stronger storms,
   which could include isolated short-lived supercell structures,
   before activity diminishes Saturday evening.

   ...Central Plains...
   In the presence of modestly steep mid-level lapse rates, models
   continue to suggest that a corridor of moderate mixed layer CAPE
   (1000-2000+ J/kg) may develop within the lee surface trough, across
   parts of western Kansas into western and central Nebraska by late
   Saturday afternoon.  With sharp turning of low through mid-level
   wind fields perhaps contributing to modest vertical shear within
   otherwise weak deep layer mean flow, the environment appears at
   least potentially supportive of scattered severe storm development,
   including isolated supercells.  Forcing to support the initiation of
   storms is more unclear, but models indicate that a very weak
   mid-level perturbation may cross the region during the late
   afternoon/early evening hours.

   ..Kerr.. 08/18/2017

   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z