Convective Outlook

U.S. Severe Weather Forecast

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swody1 
Storm Prediction Center ac 250539 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1239 am CDT Sat may 25 2013 


Valid 251200z - 261200z 


..there is a slight risk of severe thunderstorms central through northern High 
Plains... 


... 


Synoptic pattern will undergo little change Saturday with an upper 
ridge over the central U.S. Flanked by troughs over the western and eastern 
states. At the surface a Lee trough/dryline will persist over the High 
Plains while a warm front lifts slowly northward through the central/northern 
plains. 


..cntrl and northern plains area... 


Southeasterly winds east of Lee trough will advect upper 50s dewpoints into 
the northern High Plains with low-middle 60s farther south over the Central 
Plains. Meanwhile...west-southwesterly winds aloft will advect steep middle-level 
lapse rates above the moistening boundary layer contributing to an 
axis of 1500-2500 j/kg MLCAPE. The atmosphere will remain capped to 
surface based storms until middle afternoon when diabatic warming will 
augment orographic forcing where a moist southeasterly upslope regime will 
exist from northestern Colorado...eastern Wyoming into eastern Montana. Storms are expected to 
develop over the higher terrain and subsequently spread eastward into the 
axis of moderate instability across the High Plains. This region 
will reside on southern fringe of stronger flow aloft with 35-40 knots winds 
at 500 mb above southeasterly near surface winds resulting in favorable vertical 
shear for supercells. Very large hail will be the initial primary 
threat...through isolated tornadoes may also be possible. A few 
storms may eventually congeal into lines/clusters with an increasing 
damaging wind threat during the evening...sustained by a 
strengthening southerly low level jet. Severe threat is expected to gradually wane 
toward late evening. 


..srn High Plains... 


Isolated to widely scattered storms are expected to once again 
develop over the higher terrain and spread eastward into the southern High 
Plains. These storms will exist in a weak shear environment...but 
steep lapse rates...moderate instability and 25+ f low level 
temperature-dewpoint spreads will support a threat for isolated 
large hail and downburst winds. 


.Dial/Dean.. 05/25/2013 

Mesoscale Discussion

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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 250450 
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Mesoscale discussion 0794 
National Weather Service Storm Prediction Center Norman OK 
1150 PM CDT Friday may 24 2013 


Areas affected...S central and central Nebraska 


Concerning...severe potential...watch possible 


Valid 250450z - 250545z 


Probability of watch issuance...40 percent 


Summary...storms will continue to congeal into an mesoscale convective system across S 
central/central Nebraska the next few hours...with isolated large hail 
the main threat. A new Severe Thunderstorm Watch will be possible. 


Discussion...convection continues to develop across S central into 
central Nebraska in a zone of increasing low-level warm air advection...on the nose of a 
50 knots low level jet. The storms currently reside in the lingering instability 
axis across S central Nebraska...with instability expected to diminish 
gradually overnight and with eastward extent. As such...there will be a 
risk of primarily large hail in the next couple of hours when the 
storms are at their peak and still maintain some supercell 
structure. The convection will also tend to become a little more 
elevated with time as the surface layer cools...which will become 
more hostile for damaging gusts at the surface. The situation will 
be discussed with the weather forecast office Hastings to determine the need for a new 
Severe Thunderstorm Watch. 


.Thompson/guyer.. 05/25/2013 


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


Attention...WFO...oax...Gid...lbf...gld... 


Latitude...Lon 41479731 40959723 40579765 40269860 40050025 40340096 
40880108 41460057 41999939 42109810 41859756 41479731