U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 251953 
Storm Prediction Center ac 251952 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0252 PM CDT Fri may 25 2018 

Valid 252000z - 261200z 

..there is a slight risk of severe thunderstorms across parts of 
the upper Mississippi Valley and Southern Plains... 

Severe thunderstorms are possible this afternoon 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 couple changes have been made to the outlook for this issuance. 
The first change is to expand the slight risk area in the upper 
Mississippi Valley westward across most of western Wisconsin where 
Severe Thunderstorm Watch 120 is located. The second change is to 
add a 2 percent tornado and significant hail contour in parts of 
western Oklahoma/eastern Texas Panhandle southward into northwest 
Texas where strong instability is analyzed by the rap and regional 
WSR-88D vwps show moderate deep layer shear. 

.Broyles.. 05/25/2018 

Previous discussion... /issued 1121 am CDT Fri may 25 2018/ 

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. 


Mesoscale Discussion

acus11 kwns 251951 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 251950 

Mesoscale discussion 0520 
National Weather Service Storm Prediction Center Norman OK 
0250 PM CDT Fri may 25 2018 

Areas affected...portions of northern and central Maine 

Concerning...severe potential...watch unlikely 

Valid 251950z - 252145z 

Probability of watch issuance...20 percent 

Summary...strong to severe storm are possible this afternoon with an 
associated severe wind and hail risk. A ww is not likely at this 

Discussion...storms have formed along a surface boundary in western 
Quebec this afternoon and are quickly moving east into northern 
Maine. While buoyancy remains limited -- MUCAPE is analyzed to be 
around 500 j/kg -- strong flow aloft has contributed to 30-65 kts of 
effective bulk shear per rap analysis. Given the large shear values, 
storm organization will be sufficient to present a severe wind and 
hail threat. However, limited buoyancy and coverage of storms will 
not necessitate a ww at this time. 

.Wendt/Hart.. 05/25/2018 

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


Latitude...Lon 46936886 46766788 46366768 45806768 45606818 45686916 
45816986 45977017 46267032 46747021 47076980 46936886