U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus02 kwns 281755 
Storm Prediction Center ac 281754 

Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1254 PM CDT Wed Jun 28 2017 

Valid 291200z - 301200z 

..there is an enhanced risk of severe thunderstorms across eastern 
Nebraska and Kansas into far northwest Missouri and southwest 

..there is a slight risk of severe thunderstorms surrounding the 
enhanced risk area across much of Nebraska and Kansas to Southern 
Lower Michigan and Northern Ohio... 

..there is a marginal risk of severe thunderstorms surrounding the 
slight risk area from Wyoming and western South Dakota and the Central High plains 
to western and northern Pennsylvania into New York... 

Scattered significant severe thunderstorms are most likely Thursday 
into Thursday evening across the Central Plains, with areas of large 
hail and damaging winds. Isolated strong to severe storms are also 
possible across the Midwest eastward into western and northern 
Pennsylvania and New York, and across the Central High plains to 
Wyoming, South Dakota to southwest Minnesota. 

Low-amplitude midlevel shortwave troughs will track east-northeast 
across the Dakotas and mid MO valley through the Great Lakes, 
Midwest to the northeast states Thursday and Thursday night. 
Meanwhile, a large-scale midlevel trough, currently tracking 
equatorward through southwest Canada per water vapor imagery, is 
expected to move southeast reaching the central rockies/High Plains 
by 12z Friday. A warm front attendant to a midlevel trough shifting 
east from the upper Great Lakes region should extend from northern 
lower Michigan into southern Ontario. Meanwhile, the Iowa to the NE and 
northern Kansas portion of a trailing cold front from the upper Great 
Lakes should be the focus for thunderstorm development this forecast 
period. Additional storms will be possible attendant to surface 
trough moving east across the Dakotas and a separate cold front 
advancing south through the northern High Plains. 

..Central Plains region... 
Models continue to suggest the greatest coverage of severe storms 
Thursday afternoon through Thursday evening should occur across the 
initial day 2 enhanced risk area from eastern portions of NE/Kansas into 
southwest Iowa and far northwest MO. This region will have the 
greatest juxtaposition of high surface moisture (dew points in the 
upper 60s to around 70 f) beneath steep midlevel lapse rates 
(exceeding 8 c/km) and diabatic heating, resulting in moderate 

Despite some height rises in the wake of an early period midlevel 
impulse across eastern NE/northeast KS, sufficient deepening of 
boundary layer moisture and strong surface heating will result in a 
reduction of mlcinh for thunderstorm development near the 
aforementioned cold front and any differential heating boundaries 
from early morning ongoing showers and storms. Height falls ahead 
of the approaching upstream larger scale northwest U.S. Trough will 
support thunderstorm development Thursday afternoon and evening. 
Strengthening westerly midlevel winds across the Central Plains and 
south-southwesterly low-level winds into eastern Kansas/northwest MO 
suggest strong effective bulk shear will support organized storms 
including supercells. Large hail, some very large, and a potential 
tornado threat into southeast NE/northeast Kansas to southwest Iowa and 
northwest MO will be the initial severe hazards. 

Meanwhile, model-to-model and run-to-run consistencies in the 
NAM/GFS/ECMWF suggest storms in the Central High plains could evolve 
into a forward-propagating mesoscale convective system Thursday night across mainly central 
and eastern KS, with damaging winds being the primary severe threat, 
as heights falls and further strengthening of deep-layer winds --- 
with the approach of the upstream large-scale trough. 

..Midwest into western PA and New York... 
Although a synoptic warm front should be located farther north into 
northern lower Michigan into southern Ontario, a differential heating 
boundary extending from Southern Lower Michigan through northern Illinois should 
be the primary focus for new thunderstorm development Thursday 
afternoon and evening. The 15% (slight) and 5% (marginal) 
severe-risk areas have been expanded a little northward to include 
more of northern Illinois and southern lower mi, with this change based on 
model consensus (12z NAM/GFS and 00z ecmwf) for the placement of 
showers and thunderstorms in vicinity of the aforementioned surface 
boundary. Moderate instability and sufficient bulk shear oriented 
parallel to the convective initiating boundary suggest line segments 
with locally strong/damaging winds being the primary threat. 

Farther northeast, stronger west-southwesterly low-level winds 
(40-50 kt) from northern PA into New York should result in a threat for 
damaging winds as storms develop across a destabilizing warm sector 
Thursday afternoon. 

..WY/western South Dakota... 
Marginal instability combined with forcing for ascent attendant to 
the larger scale trough moving toward the central rockies and 
northern High Plains, and in vicinity of a cold front should allow 
for afternoon to early evening thunderstorm development. Weak to 
modest bulk shear should limit the overall severe weather threat, 
though steep low-level lapse rates could enhance locally 
strong/damaging winds gusts. 

..eastern South Dakota/southwest Minnesota... 
Effective bulk shear and forcing for ascent attendant to a midevel 
shortwave trough moving east across ND/South Dakota during this forecast 
period should support storm development, with some organized. 
Greatest severe threat, though a marginal risk due to weak 
instability, is possible across eastern South Dakota and southwest Minnesota. 

.Peters.. 06/28/2017