Jun 9, 2018 2000 UTC Day 1 Convective Outlook
Updated: Sat Jun 9 19:59:51 UTC 2018 (20180609 2000Z Day 1 shapefile | 20180609 2000Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180609 2000 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
ENHANCED 18,430 1,437,388 Cedar Rapids, IA...Davenport, IA...Waterloo, IA...Iowa City, IA...Moline, IL...
SLIGHT 73,200 2,060,350 Peoria, IL...Rochester, MN...Missoula, MT...Dubuque, IA...Great Falls, MT...
MARGINAL 274,940 35,394,712 Indianapolis, IN...Columbus, OH...Baltimore, MD...Washington, DC...St. Louis, MO...
Probabilistic Tornado Graphic
20180609 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 % 22,652 1,468,522 Cedar Rapids, IA...Davenport, IA...Waterloo, IA...Iowa City, IA...Moline, IL...
2 % 20,682 1,133,699 Rochester, MN...Dubuque, IA...Mankato, MN...Galesburg, IL...Clinton, IA...
Probabilistic Damaging Wind Graphic
20180609 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
30 % 18,430 1,437,388 Cedar Rapids, IA...Davenport, IA...Waterloo, IA...Iowa City, IA...Moline, IL...
15 % 72,976 1,892,697 Peoria, IL...Missoula, MT...Dubuque, IA...Great Falls, MT...Quincy, IL...
5 % 273,065 35,347,390 Indianapolis, IN...Columbus, OH...Baltimore, MD...Washington, DC...St. Louis, MO...
Probabilistic Large Hail Graphic
20180609 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
15 % 54,641 2,464,745 Cedar Rapids, IA...Davenport, IA...Rochester, MN...Waterloo, IA...Iowa City, IA...
5 % 175,528 17,684,966 Baltimore, MD...Washington, DC...St. Louis, MO...Arlington, VA...Rockford, IL...
   SPC AC 091959

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0259 PM CDT Sat Jun 09 2018

   Valid 092000Z - 101200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
   OF EASTERN IOWA AND NORTHWEST ILLINOIS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
   CENTRAL AND WESTERN MONTANA...

   ...SUMMARY...
   A cluster of severe storms with a few tornadoes, damaging winds, and
   large hail is anticipated late afternoon into tonight across eastern
   Iowa and vicinity.  A few storms producing severe wind gusts are
   expected this afternoon into early evening across western Montana.

   Destabilization continues across central/eastern IA and northwest IL
   in the wake of morning thunderstorms, with strong to occasionally
   severe storms occurring early this afternoon over northeast IA. 
   Please refer to Mesoscale Convective Discussion 682 for mesoscale
   details in this area.

   Across central/western MT, heating/destabilization continues in
   advance of an upper-level trough approaching from the west, and an
   increase in thunderstorm coverage and intensity is expected over the
   next several hours.  Refer to MCD 683 for the latest short-term
   thinking in this area.

   Elsewhere, thunderstorms were loosely organized along the OH/IN
   border and extending south into western KY in association with a
   remnant MCV interacting with a quasi-stationary front and residual
   outflow boundaries.  These storms have a history of isolated
   marginally severe hail and strong wind gusts, and this risk will
   continue into the early evening hours given weak/pockets of moderate
   surface-based buoyancy.

   Along the mid-Atlantic coast/Delmarva region, strong to severe
   storms will continue through the remainder of the afternoon in the
   vicinity of a stationary front.  A very moist air mass (PW values in
   excess of 1.75 inches) has contributed to moderate surface-based
   instability, and westerly deep shear vectors of 30-35 kts will
   promote some degree of updraft organization.

   Only minor adjustments were made to the risk areas in the previous
   outlook.

   ..Bunting.. 06/09/2018

   .PREV DISCUSSION... /ISSUED 1127 AM CDT Sat Jun 09 2018/

   ...Eastern IA vicinity...
   A mesoscale setup for a few supercells capable of all hazards
   transitioning to a bowing MCS is expected this evening. Moderate
   diabatic heating is underway across much of western and central IA
   in between morning convection across eastern IA and southern MN.
   This will contribute to substantial destabilization with MLCAPE
   reaching 1500-3000 J/kg amid a pocket of residual upper 60s to lower
   70s surface dew points. Renewed surface-based storm development is
   expected by late afternoon where the southern MN MCV interacts with
   the composite front/outflow arcing along the MN/IA border into
   eastern IA. Vertical shear will be enhanced within this mesoscale
   corridor as southeast surface winds are maintained beneath a
   confined swath of stronger mid-level westerlies south of the MCV. A
   few supercells producing large hail and tornadoes are expected
   through early/mid-evening. However, convection should subsequently
   evolve into another southeast-moving MCS across eastern IA into
   western IL tonight with damaging winds becoming the predominant
   hazard.

   ...Western MT...
   An amplified mid-level trough over the Pacific Northwest will
   progress east across the northern Rockies through tonight. This
   trough and a strong associated cold front will begin to affect
   western MT this afternoon. Intense surface heating is expected ahead
   of the front, yielding a deeply mixed thermodynamic profile as
   surface dew points mix into the 40s and lower 50s. Forcing for
   ascent will be focused along the sharpening front and a few storms
   should form along it by mid-afternoon, spreading north-northeast
   toward the Alberta border through early evening. Severe wind gusts
   will be the main threat with the high-based supercells, though steep
   lapse rates will also support a risk of isolated large hail mainly
   through the late afternoon portion of the convective life cycle.

   ...Midwest to Mid-Atlantic...
   Moderate buoyancy is expected along and south of a quasi-stationary
   front draped across these regions. Scattered storms will be focused
   this afternoon in the Mid-Atlantic portion of the boundary. Loosely
   organized clusters should evolve from remnant MCVs in vicinity of
   the front across the Midwest and OH Valley. With predominantly weak
   vertical shear, isolated downburst winds will be the main
   threat.

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