U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 190054 
Storm Prediction Center ac 190053 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0753 PM CDT Mon Jun 18 2018 

Valid 190100z - 191200z 

..there is a slight risk of severe thunderstorms across portions of 
the Central Plains and middle MO valley... 

Isolated severe thunderstorms are expected this evening across the 
Central High plains, mid-Missouri Valley, and portions of southern 
New England and the northern middle Atlantic. 

..Central High plains... 

Deep convection is finally developing along the Front Range of Colorado 
where moist upslope flow has persisted for much of the day. Delayed 
heating has slowed this development but 19/00z sounding from dnr 
suggests ample buoyancy and shear exists for sustained rotating 
updrafts. Isolated supercells are expected across portions of 
northeast Colorado into southeast Wyoming and hail is the primary threat. 

..mid-MO valley... 

Complex convective scenario continues across eastern NE into western 
Iowa ahead of a weak mid-level short-wave trough that is ejecting 
northeast into this region. Considerable amount of precipitation and 
convective outflow has overturned much of the instability across 
this part of the country, although strong instability persists in 
the wake of the short wave immediately ahead of the surface front. 
Frontal convergence, aided by outflow interactions may contribute to 
isolated severe across this area. 

..northern middle Atlantic and southern New England... 

Pre-frontal bands of convection have migrated across much of the 
northeast, overturning the buoyancy necessary for severe 
thunderstorms. While synoptic front will soon advance south of the 
international border, severe thunderstorms are not expected along 
this boundary as it surges southeast. Strongest convection over the 
next few hours will be along the southern New England coast, arcing 
into central PA where instability is currently sufficient for the 
maintenance of robust updrafts. 

.Darrow.. 06/19/2018 


Mesoscale Discussion

acus11 kwns 190232 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 190231 

Mesoscale discussion 0787 
National Weather Service Storm Prediction Center Norman OK 
0931 PM CDT Mon Jun 18 2018 

Areas affected...portions of northeast Colorado...and into southeast 
Wyoming and southwest portions of the Nebraska Panhandle 

Concerning...Severe Thunderstorm Watch 189... 

Valid 190231z - 190430z 

The severe weather threat for Severe Thunderstorm Watch 189 

Summary...severe weather risk continues -- particularly over the 
northeast Colorado vicinity. 

Discussion...latest radar loop reveals continued regeneration of 
updrafts along the Colorado Front Range, primarily in the 
Denver/Boulder vicinity. Where low-level winds are backed north of 
the weak low-level cyclone, shear remains supportive of 
rotating/supercell storms, and indeed several cells have shown at 
least transient updraft rotation. A couple of stronger supercells 
are ongoing as well, and remain capable of producing large hail and 
locally damaging winds, and possibly a brief tornado -- including a 
pair of long-lived cells now near the Weld/Morgan County line. 

With that said, there is evidence of some cell mergers/possible 
beginnings of some upscale/linear growth, and this evolution is 
hinted at by some of the latest cam guidance. Some propagation of 
this upscale-growing convection eastward along the I-76 corridor is 
expected, accompanied by local risk for damaging winds and hail in 
the short term. 

Meanwhile, with the airmass gradually stabilizing, and the 
expected/gradual transition from cellular to banded convection, 
severe risk should begin to gradually diminish over the next couple 
of hours as storms become elevated above a slowly stabilizing 
boundary layer. 

.Goss.. 06/19/2018 

..please see www.Spc.NOAA.Gov for graphic product... 


Latitude...Lon 42700451 42210378 41530265 39550290 39420491 39980523 
40950496 41460526 41960470 42700451