U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 270100 
Storm Prediction Center ac 270059 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0759 PM CDT Sat may 26 2018 

Valid 270100z - 271200z 

..there is a slight risk of severe thunderstorms over a portion of 
the northern High Plains and southern Florida... 

Severe storms with damaging wind and large hail are expected over 
the northern High Plains this evening into the overnight. A threat 
for a couple of tornadoes will persist over South Florida. 

..northern High Plains... 

Storms are in the process of developing along a cold front across 
central Montana as well as over the higher terrain. Southeasterly winds 
have become established in the downstream warm sector in association 
with a Lee trough, maintaining a corridor of low 50s f surface 
dewpoints over eastern Montana beneath steep lapse rates. Objective 
analysis and 00z radiosonde observation data show A Reservoir of 1500-2000 j/kg MLCAPE 
from eastern Montana into southwest ND and western South Dakota. Despite presence 
of an upper ridge and onset of nocturnal cooling, several embedded 
vorticity maxima and a strengthening low-level jet will Foster the 
maintenance of storms through the High Plains including ND through 
the evening and into tonight. Wind profiles with 30-40 kt effective 
bulk shear will support some high based supercell structures with 
initial discrete development. However, activity may eventually 
congeal into one or more forward propagating clusters as they 
continue east during the evening. The steep lapse rate environment 
with inverted-v low-level thermodynamic profiles will promote a 
threat for damaging wind, but large hail will also be possible, 
especially through mid evening with any discrete supercell 

..South Florida... 

Subtropical storm Alberto is forecast by the NHC to continue north 
into the eastern Gulf, but with the center well west of the Florida 
Peninsula. However, the outer bands are already starting to affect 
South Florida and the Keys. Vwp data from Key West and Miami already show 
veering wind profiles in the 0-2 km layer with around 150-200 m2/s2 
storm relative helicity, and further enlargement of low-level 
hodographs will occur tonight. However, much of the southern 
peninsula has been affected by widespread stratiform rain resulting 
in moist adiabatic profiles and very weak instability. Nevertheless, 
at least some risk for a couple of tornadoes will exist within the 
outer bands of Alberto as the storm continues north tonight. See 
latest discussion from NHC for more information on Alberto. 

.Dial.. 05/27/2018 


Mesoscale Discussion

acus11 kwns 270313 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 270313 

Mesoscale discussion 0535 
National Weather Service Storm Prediction Center Norman OK 
1013 PM CDT Sat may 26 2018 

Areas affected...northeast Montana and western North Dakota 

Concerning...Severe Thunderstorm Watch 122... 

Valid 270313z - 270515z 

The severe weather threat for Severe Thunderstorm Watch 122 

Summary...thunderstorm development continues across northeast 
Montana. Coverage should continue to increase in the next couple of 
hours before a thunderstorm cluster moves east into North Dakota. 
Hail and strong, gusty thunderstorm outflow will continue to be 

Discussion...more robust thunderstorm development, as evidenced by 
recent 1.75-2.00 inch hail reports, has occurred within the last 
hour across McCone, Dawson, and Richland counties. These 
thunderstorms, along with those to the northwest, will continue to 
mature over the next couple of hours. The resulting congealing 
thunderstorm outflows should help develop a mesoscale convective 
system (mcs) that will move east during the evening and early 

Deep-layer shear of 30 knots should slowly increase through the 
evening as a mid-level jet streak approaches the area. Most-unstable 
cape values at or above 2000 j/kg are found across eastern Montana 
but is less farther east across western North Dakota. However, a 
strengthening southwesterly low-level jet should allow enough 
low-level moisture advection for a slight increase in instability 
across North Dakota ahead of the developing mesoscale convective system. The result will be 
an environment conducive for the maintenance of the eventual mesoscale convective system as 
it moves east into North Dakota. 

Large hail and strong, gusty thunderstorm outflows will be possible 
in the next couple of hours, with a transition to more of a wind 
threat thereafter. 

.Marsh.. 05/27/2018 

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


Latitude...Lon 46390673 46950758 48200750 48820654 48500451 47560210 
46300162 45290243 45450363 45900516 46390673