U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 181942 
Storm Prediction Center ac 181941 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0241 PM CDT Mon Jun 18 2018 

Valid 182000z - 191200z 

..there is a slight risk of severe thunderstorms across parts of 
the Central High plains...middle Missouri Valley and northeast... 

Severe thunderstorms will be possible this afternoon and evening 
across parts of the northeastern states, middle Missouri Valley, and 
northeast Colorado into southeast Wyoming. 

The only change to the outlook for this issuance is to remove 
thunder from parts of Kentucky and southern Ohio where a 
thunderstorm or convection is in the vicinity. 

.Broyles.. 06/18/2018 

Previous discussion... /issued 1129 am CDT Mon Jun 18 2018/ 

..northeast states from primarily New York into New England... 
An upper low over Quebec is forecast to move toward the 
east-southeast through tonight, with mid-level heights falling over 
the discussion area as a band of stronger winds aloft shift 
southward with time. Very warm and moist low-levels are indicated 
on 12z regional soundings and latest surface data with surface 
temperatures in the 80s to near 90f and dew points in the upper 60s 
to lower 70s across central and southern New York eastward into 
parts of New England. From a thermodynamic perspective, this is 
tempered by warm mid-level temperatures resulting in weak mid-level 
lapse rates over the region. Nevertheless, continued diabatic 
heating from New York into much of New England will contribute to 
further destabilization with MLCAPE of 1000-1500 j/kg later this 

As a cold front moves southeast across the region mainly tonight, 
multiple bands of storms are expected to develop along and ahead of 
the front as a weakening cap permits lifted parcels to reach the 
level of free convection. Vertical shear will be stronger with northward extent over the 
area and is expected to be sufficient for organized mainly 
multi-cell clusters and bands to develop, although isolated 
supercells will also be possible. The strong westerly component of 
flow above the boundary layer coupled with steepening low-level 
lapse rates also suggests potential for bowing segments to form. 
The primary threat will be damaging wind gusts with stronger cells 
this afternoon into the early portions of tonight. See Maryland 779 for 
additional near term details. 

..eastern Nebraska into Iowa... 
Water vapor imagery shows a well-defined short-wave trough lifting 
northeast over the Central High plains. An associated weak surface 
low is forecast to move into eastern Nebraska this afternoon along a 
quasi-stationary front that extends into Iowa. Limited clouds over 
southeast and south central Nebraska will promote strong diabatic 
heating within an air mass characterized by surface dew points in 
the low 70s, with resultant MLCAPE of 1500-2000 j/kg expected this 
afternoon. A few storms are likely to develop by mid-late afternoon 
near the low and along the front into Iowa where low-level 
convergence will be maximized as the large scale ascent associated 
with the short-wave trough overspreads the region. Veering wind 
profiles with height, especially along and north of the front, will 
be supportive of organized storms including a few supercells. 
Stronger cells will be capable of producing large hail, damaging 
winds and possibly several tornadoes into the evening hours. 

..northeast Colorado into southeast Wyoming... 
Low clouds currently over this region are expected to diminish this 
afternoon as southeast upslope winds gradually develop in the wake 
of the aforementioned short-wave trough over the High Plains. 
Low-level moisture is likely to persist with surface dew points 
remaining in the low 50s, and as diurnal heating commences the 
environment will become increasingly unstable with MLCAPE of 
1000-1500 j/kg. 

A few storms are expected to develop later this afternoon and 
evening and spread eastward as mid-level winds increase over the 
area. Strong directional shear with height will support supercell 
development with large hail and damaging wind gusts the primary 
threat into the evening hours. 


Mesoscale Discussion

acus11 kwns 182155 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 182155 

Mesoscale discussion 0784 
National Weather Service Storm Prediction Center Norman OK 
0455 PM CDT Mon Jun 18 2018 

Areas affected...eastern Pennsylvania...northern New Jersey...far 
southeast New York...Connecticut...northern Rhode 

Concerning...severe potential...watch possible 

Valid 182155z - 190000z 

Probability of watch issuance...40 percent 

Summary...isolated damaging wind gusts and marginally severe hail 
possible, especially in portions of New England. Convective trends 
are being monitored for a ww. 

Discussion...loosely organized clusters are in progress across 
portions of New England down into the Hudson Valley. The ambient 
environment is characterized by deep moisture, with precipitable water values of 
up to 2 inches in some locations, especially over New England. Rich 
low-level moisture and strong surface heating is the main source of 
buoyancy, given poor mid-level lapse rates (5.5 c/km on average). 

Given modest mid-level flow and associated effective bulk shear 
along with modest instability, the severe threat is expected to be 
isolated in extent. Marginally severe hail is possible, along with 
damaging wind gusts induced by wet downbursts. As storms are driven 
primarily by the strong surface heating, a decrease in coverage and 
intensity is expected after sunset. Storms may also weaken as they 
approach the marine layer situated near the coast. 

A ww is currently not anticipated but convective trends will be 

.Squitieri/jirak/guyer.. 06/18/2018 

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


Latitude...Lon 40787689 40777636 41117547 41687443 42197355 42477230 
42517202 42667167 42687148 42667123 42617094 42577089 
42127111 41667179 41167316 40587388 40217454 40197517 
40417626 40787689