U.S. Severe Weather Forecast (Convective Outlook)

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Day Three

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acus03 kwns 250730 
swody3 
Storm Prediction Center ac 250729 


Day 3 convective outlook corr 1 
National Weather Service Storm Prediction Center Norman OK 
0229 am CDT Sat may 25 2019 


Valid 271200z - 281200z 


..there is a slight risk of severe thunderstorms from portions of 
the Central Plains eastward to the Midwest... 


Corrected for 5% label 


... 
Strong to severe storms are possible from Nebraska eastward to the 
Midwest. Isolated severe storms are possible from northern Kansas 
southward through West Texas. 


... 
Severe potential on d3/Monday will be tied to an approaching 
mid-level cutoff low that should reach the central rockies by the 
end of the period. A belt of strong mid-level flow will exist on 
the southeastern periphery of the mid-level low, but this jet should 
remain mostly west of a surface dryline that will extend from 
southwestern Nebraska southward through West Texas through much of 
the day. Downstream, shortwave ridging will exist across the 
Missouri River valley during the afternoon, while shifting eastward 
overnight. At the surface, a low will organize in eastern Colorado 
throughout the period, while a warm front extends across central 
Nebraska northeastward to southern Wisconsin. A buoyant airmass 
will reside south of this boundary throughout the forecast period. 


... 
Primary indications are that convection will be tied to the warm 
front through most of the forecast period, with strong capping and 
subsidence evident across the open warm sector through late in the 
period. Steep lapse rates aloft (especially over nebraska) will 
Foster hail with mostly elevated cells that form near the front, 
though any cells that can ingest surface-based parcels and reside 
near the warm front will have a risk of damaging wind and tornadoes. 
Guidance suggests that multiple rounds of convection may traverse 
this boundary through the forecast period. 


The greatest chance of warm-sector convection will exist across 
southern Nebraska and northwestern Kansas along and ahead of a Stout 
dryline. This risk should be greatest after 00z when forcing for 
ascent finally reaches the northwestern extent of the warm sector 
and weakens the cap. Supercellular shear profiles will Foster storm 
organization, while strong instability and steep mid-level lapse 
rates will Foster hail and damaging wind gusts. The tornado threat 
is a bit conditional in this area and will depend on timing of 
convective development - if storms develop too late in the forecast 
period they will likely be slightly elevated. Storms that can form 
earlier in the day will pose a threat of all severe hazards. 


Across western Nebraska, easterly low-level flow just north of the 
front may bring 50s f dewpoints up against higher terrain in 
Wyoming. A few thunderstorms may result, with shear profiles 
supportive of updraft rotation along with an attendant threat for 
hail, wind and perhaps an isolated tornado. Some uncertainty exists 
with this scenario, however, with some models suggesting more of a 
northerly component to low-level flow and stable low-levels. 


..southern Wisconsin, Illinois, Indiana... 
Early-day convection may alter the position of a surface warm front, 
which models inconsistently depict across the area. By late 
afternoon, however, models hint at the potential for a few 
surface-based storms to develop south of the warm front, which seems 
plausible as models also indicate the passage of a mid-level 
shortwave trough just north of the region during peak heating hours. 
Should these storms materialize, they will reside in a strongly 
buoyant airmass, with vertical shear profiles favoring supercellular 
storms. Model inconsistencies lend greater-than-usual uncertainty, 
although the warm-sector environmental parameter space suggests that 
conditional marginal/slight risks are appropriate. 


..northern Kansas southward to Texas... 
Models generally depict only isolated storm development along the 
dryline - most likely after 03z. This seems plausible given the 
late arrival of forcing and eastward shift of the dryline beginning 
after dark. Any storms that can develop along this boundary will 
have a threat for large hail and damaging wind gusts, but will also 
struggle against mid-level inhibition. Thus, the severe threat in 
this area is conditional. 


.Cook.. 05/25/2019 


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