SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1230 AM CDT Tue May 04 2021

Valid 041200Z - 051200Z


Widespread strong to severe thunderstorm development is probable
today across the Deep South.  The primary risk will be scattered
severe gusts resulting in wind damage and an accompanying risk for a
few tornadoes.

A mid-level shortwave trough initially near the OK/AR border this
morning, will move east and reach the central/southern Appalachians
by early Wednesday morning.  An effective cold front modulated by
convection at the start of the period, is forecast to move east
across the lower MS Valley and OH Valley/Mid-South during the day. 
A weak surface low is forecast to migrate northeastward from AR to
the lower Great Lakes.  

...Southeast and northern Gulf Coast...
A couple of thunderstorm clusters/MCSs are forecast this morning
across the OH Valley south-southwestward into the lower MS Valley
and east TX near the aforementioned surface boundary.  The risk for
damaging gusts will probably accompany one or more of these
thunderstorm clusters given moderate instability and a moisture-rich
airmass.  Model guidance varies considerably regarding the evolution
of a probable thunderstorm cluster located over KY/TN during the
morning.  A portion of this convective band may continue into
northern AL/GA and be aided by the nose of a 35-kt LLJ situated over
MS at daybreak.  It is less clear if storms rejuvenate farther east
near the Cumberland Gap and parts of VA/NC during the day or if the
focus for thunderstorms is shunted farther south over GA/Carolinas. 
Given a very moist and very unstable airmass sampled Monday night
along the northern Gulf Coast (reference the 00 UTC Slidell, LA raob
featuring an 18 g/kg mean mixing ratio and 3500 J/kg MLCAPE), it is
plausible a couple of organized thunderstorm bands will develop
coincident with the diurnal heating cycle.  The m-shaped hodographs
due in part to the positive-tilt character of the mid-level trough,
in combination with high PW, will favor upscale growth with
developing storms.  It appears a swath of damaging gusts is most
probable from parts of MS east through parts of AL.  A gradual
diminishing in thunderstorm intensity is expected by the mid evening

...OH Valley and Mid-Atlantic states...
Isolated to scattered thunderstorms are forecast to develop during
the day on the northern periphery of a moist/unstable sector. 
Relatively large uncertainty exists with convection potentially
limiting the degree of destabilization, especially across parts of
the OH Valley during the day.  Nonetheless, it seems an isolated
risk for damaging gusts and perhaps hail may accompany the stronger
storms before this activity weakens during the evening.

..Smith/Lyons.. 05/04/2021

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