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.)
Some Larger Population Centers in Risk Area
Cedar Rapids, IA...Davenport, IA...Waterloo, IA...Iowa City, IA...Moline, IL...
Peoria, IL...Missoula, MT...Dubuque, IA...Great Falls, MT...Quincy, 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...
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
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
.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
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
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