U.S. Severe Weather Forecast (Convective Outlook)

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acus02 kwns 231727 
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Storm Prediction Center ac 231726 


Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1226 PM CDT sun Apr 23 2017 


Valid 241200z - 251200z 


..there is a marginal risk of severe thunderstorms Monday across 
the Carolina coastal plain and parts of the adjacent Piedmont... 


... 
Thunderstorms accompanied by at least some severe weather potential 
may impact the Carolina coastal plain and portions of the adjacent 
Piedmont Monday. 


... 
Models indicate that a strong belt of westerlies, traversing much of 
the mid-latitude Pacific into the interior western U.S., Will 
undergo some amplification during this period. As broad mid/upper 
ridging builds across the eastern Pacific through the U.S. Pacific 
coast, broad downstream troughing appears likely to evolve near the 
nose of the stronger flow, across the Great Basin and rockies. In 
lower levels, an initial surface cyclone, developing to the Lee of 
The Rockies in association with this regime, appears likely to 
migrate northeast of the Black Hills region and weaken during the 
day Monday, with new surface cyclogenesis taking place near/north of 
the Texas/Oklahoma Panhandle region late Monday through Monday 
night. 


Meanwhile, within split westerlies downstream of The Rockies, broad 
ridging within the northern stream is expected to build across and 
northeast of the Great Lakes region. Within the southern stream, 
troughing over the southeast may gradually pivot from a neutral to 
negative tilt while progressing east of the Atlantic coast. As it 
does, a modest embedded lower/mid tropospheric cyclone is forecast 
to redevelop from near or just south of the southern Appalachians 
into areas near or east of the Carolina coast by 12z Tuesday. 
Appreciable spread is evident among the various models, and within 
their respective ensemble output, concerning these developments and 
possible interaction/consolidation with an impulse within the 
subtropical westerlies (now progressing across/northeast of southern 
Florida and the bahamas). 


..South Atlantic coast... 
It remains unclear what, if any, impact that the model spread 
concerning the evolution of the synoptic system will have on the 
forecast for this period. Even though it appears that the highest 
moisture content air (characterized by 70f+ surface dew points) will 
generally remain confined to areas well offshore, a substantive 
influx of moisture still seems likely across/inland of the Carolina 
coast. This is expected to contribute to sufficient destabilization 
for considerable convective development. The extent to which 
mid-level cooling is able to steepen lower/mid tropospheric lapse 
rates remains uncertain, and it is not clear that there will be 
sufficient breaks in the overcast across inland areas to allow for 
appreciable surface heating. Deep layer mean wind fields and shear 
within the warm sector of the low may not be much more than 30 kt. 
However, it may not be out of the question that the environment 
could become conducive to thunderstorms with at least some severe 
weather potential, mainly across parts of the South Carolina 
Piedmont into coastal plain during the day Monday, and perhaps the 
North Carolina coastal plain Monday night. 


..nrn intermountain region/rockies into north Central Plains... 
Steepening of lapse rates associated with mid-level cooling, and the 
northeastward advection of elevated mixed layer air to the Lee of 
the southern rockies, may contribute to sufficient destabilization 
for at least widely scattered thunderstorm activity, in the presence 
of favorable orographic and synoptic forcing for ascent. This 
probably will be accompanied by at least some potential for hail in 
stronger cells, including activity based within lower/mid 
tropospheric warm advection across parts of the north Central Plains 
Monday into Monday night. However, destabilization, in general, 
will be substantially inhibited across the plains by the lack of a 
substantive return flow of moisture off the Gulf of Mexico, in the 
wake of the southeastern system. And pockets of potentially 
substantive destabilization across The Rockies and intermountain 
region remain too uncertain (and likely to remain rather sparse) to 
allow a forecast of 5 percent severe probabilities at this time. 


.Kerr.. 04/23/2017 


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