U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 251622 
Storm Prediction Center ac 251621 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1121 am CDT Fri may 25 2018 

Valid 251630z - 261200z 

..there is a slight risk of severe thunderstorms over parts of 
Wisconsin and vicinity...and over parts of western Oklahoma and 
northwest Texas... 

Severe thunderstorms are possible later today into the evening over 
parts of the upper Mississippi Valley and the Southern Plains. A 
few strong to severe storms are also possible over the interior 
northwest and northern Maine. 

A long-lived mesoscale convective system has spread southward across OK into north TX, with 
the associated outflow boundary now extending from the Childress, Texas 
area eastward along the Red River. 12z cam solutions have not 
accurately portrayed the extent of the cold pool, and are likely too 
bullish on recovery of the air mass over western OK later today. 
Nevertheless, a combination of northwest flow aloft and steep mid 
level lapse rates will pose a risk of large hail and damaging winds 
with any storms that can redevelop in this region this afternoon and 
evening. Have shifted the slight risk area slightly farther west to 
capture this region. 

The leading edge of the mesoscale convective system will move into North Texas today, with a 
marginal risk of damaging winds or hail through the afternoon. 

Overnight thunderstorms are slowly weakening across WI, but have 
left multiple weak surface boundaries that may help to focus 
thunderstorm development later today. Model guidance is somewhat 
diverse in timing and location of initiation, but it appears that 
this region will have some risk of damaging winds and hail in the 
strongest cores. 12z guidance provides considerably lower 
confidence in the severe threat farther southwest into IA, so have 
trimmed the slight risk in this area. 

Stabilizing effects of the overnight mesoscale convective system over OK have lessened the 
risk of isolated strong/severe storms in Kansas and western MO, so have 
removed the marginal here. 

Scattered thunderstorms are expected this afternoon along a surface 
boundary extending from Quebec across northern ME. Forecast 
soundings suggest the potential for a few fast-moving cells capable 
of locally damaging winds and hail. 

Strong heating is occurring across this region today, with dewpoints 
in the 50s yielding afternoon MLCAPE value up to 1000 j/kg. 
Thunderstorms are expected to develop over northwest Nevada this 
afternoon and spread northward into southeast or. Other more 
isolated storms will form along an axis extending into western Idaho. 
Strengthening flow aloft and sufficient cape will promote the risk 
of a few strong cells capable of gusty winds and hail. Parts of 
this area may require an upgrade to slight risk this afternoon if 
mesoscale trends warrant. 

.Hart/Wendt.. 05/25/2018 


Mesoscale Discussion

acus11 kwns 251800 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 251759 

Mesoscale discussion 0517 
National Weather Service Storm Prediction Center Norman OK 
1259 PM CDT Fri may 25 2018 

Areas affected...southeast Minnesota...northeast Iowa...southwestern 
Wisconsin...west-central and central Wisconsin 

Concerning...severe potential...watch possible 

Valid 251759z - 252000z 

Probability of watch issuance...40 percent 

Summary...a threat for severe hail and wind gusts will evolve this 
afternoon as the atmosphere continues to destabilize. A ww will be 
possible should convective trends warrant. 

Discussion...visible satellite imagery depicts isolated convection 
initiating beneath a cirrus deck along a weak differential heating 
boundary aided by an approaching mid-level wave. Initial storms 
should remain weak. However, trends in visible satellite imagery 
indicate that the cirrus deck should depart from west to east as the 
afternoon progresses. This should help destabilize the moist air 
mass -- with dewpoints generally in the mid- to upper-60s -- and 
yield MLCAPE values of 2000-2500 j/kg. Severe wind and hail will be 
possible with the strongest storms. Some uncertainty exists with 
regard to how quickly the cirrus will depart and destabilize the air 
mass. Given the uncertainty, trends will be monitored for a possible 
ww issuance later this afternoon. 

.Wendt/Hart.. 05/25/2018 

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


Latitude...Lon 44939170 45479053 45649000 45578944 45358875 44758838 
44138885 43408971 42569078 42459133 42669224 43049279 
43909274 44939170