U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 270450 
Storm Prediction Center ac 270449 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1149 PM CDT Wed Apr 26 2017 

Valid 271200z - 281200z 

..there is a marginal risk of severe thunderstorms from portions of 
the Great Lakes region southward to the southeast states... 

..there is a marginal risk of severe thunderstorms across portions 
of southeast Colorado...western/southern Kansas...the Texas/OK 
panhandles...northern OK... 

Isolated severe wind gusts may accompany thunderstorms from portions 
of the Great Lakes region to the southeast states today into this 
evening, and across portions of the central and southern Great 
Plains late this afternoon into this evening. 

Deep surface low pressure is forecast to advance from the vicinity 
of Lake Michigan northward into Ontario, associated with a 
northward-advancing shortwave trough embedded within the eastern rim 
of broadly cyclonic flow covering the central and western states. A 
cold front will arc south from the low to the north-central Gulf 
Coast vicinity and westward. The south-central states portion of the 
front is forecast to weaken and develop northward in response to 
surface Lee cyclogenesis over the Central High plains -- enhanced by 
the emergence of a midlevel speed maximum from the central/southern 
rockies vicinity. 

..portions of the Great Lakes region southward to the southeast 
comparatively stronger deep ascent accompanying the 
northward-advancing shortwave trough is forecast to become 
increasingly displaced to the north of Richer moisture within the 
low-level cyclone's warm sector. This will tend to marginalize the 
severe potential through the period. Nevertheless, storm coverage 
and intensity are forecast to gradually increase through the diurnal 
heating cycle along and ahead of the front, with an extensive 
corridor of eastward- and northeastward-moving clusters of storms 
across the marginal risk area. Isolated damaging wind gusts should 
be the primary hazard with this activity. 

The strongest pre-frontal buoyancy related to the richest low-level 
moisture characterized by middle/upper 60s dewpoints will be 
confined to portions of central SC into Georgia and vicinity. While 
effective shear around 30-40 kt and modest low-level directional 
shear may support a few rotating updrafts, weakening low-level 
ascent will tend to limit updraft sustainability and keep any severe 
risk isolated. 

Farther north, diurnal gains in buoyancy will be muted by cloud 
coverage and more scant moisture return northward to the Great Lakes 
region and vicinity. However, sufficient low/midlevel flow could 
encourage momentum transport capable of supporting locally damaging 
wind gusts. 

Storms across the marginal risk area will weaken during the evening 
as they spread across an area from western New York southward to the SC 

..portions of southeast co, western/southern KS, the Texas/OK 
panhandles, northern OK... 
strengthening deep ascent associated with the aforementioned speed 
maximum, including isentropic ascent related to Lee cyclogenesis, 
will support the development of convective clusters in the 
steep-lapse-rate environment across the High Plains by late 
afternoon. Convection will subsequently spread eastward along a zone 
of frontogenesis through the evening hours. A dearth of moisture 
return will greatly stunt buoyancy. However, long/looping hodographs 
amid sufficient buoyancy and the steep lapse rates may support a few 
bowing convective segments capable of isolated severe wind gusts. 

.Cohen/leitman.. 04/27/2017 


Mesoscale Discussion

acus11 kwns 270458 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 270457 

Mesoscale discussion 0569 
National Weather Service Storm Prediction Center Norman OK 
1157 PM CDT Wed Apr 26 2017 

Areas affected...parts of southeastern Mississippi 

Concerning...Severe Thunderstorm Watch 167... 

Valid 270457z - 270630z 

The severe weather threat for Severe Thunderstorm Watch 167 

Summary...potential the development of an isolated supercell or two 
may linger into the 06-09z time frame, accompanied by at least the 
risk for severe hail. 

Discussion...some recent increase in thunderstorm development is 
ongoing along the pre-frontal wind shift, north/northeast of McComb 
into areas east of the Jackson area. This appears to be occurring 
on the southernmost periphery of the upper trough axis pivoting in 
negatively tilted fashion through the lower Mississippi Valley. 
Mid-level forcing for ascent appears likely to begin shifting 
northeast of the region shortly, but lower/mid tropospheric warm 
advection could maintain discrete storms into the 06-09z time frame, 
before mid-level inhibition begins to increase. In the presence of 
moderately large cape, based within or just above the boundary 
layer, a supercell or two is possible. 

.Kerr.. 04/27/2017 

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


Latitude...Lon 31398994 31818933 32068903 32198877 31758863 31218944