SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1132 PM CST Wed Jan 06 2021

Valid 071200Z - 081200Z


A very low/conditional threat for a damaging gust or brief tornado
exists across the mouth of the Mississippi eastward to just south of
the Florida Panhandle coast during the day, and the western Florida
Peninsula tonight.

A mid-level trough will traverse the Southeast states, with a 75 kt
500 mb jet overspreading the Florida Panhandle through the period. A
surface low will also progress across the Deep South. A 35+ kt 850
mb jet will encourage modest warm air advection and marginal
elevated buoyancy to move inland and promote some lightning flash
potential. However, with the latest guidance depicting more surface
based instability struggling to move ashore, severe potential will
likely be limited to areas immediately offshore. However, as a cold
front approaches the western coast of the Florida Peninsula during
the late evening (after 03Z), some surface-based instability may
advect inland ahead of a confluence band, where more organized
thunderstorm potential will exist. Elsewhere across the CONUS, A
mid-level trough, accompanied by deep-layer ascent and very modest
buoyancy may encourage a couple lightning flashes across portions of
the Pacific Northwest shoreline.  

...Portions of Florida today into tonight...
The surface cold front and an associated arcing band of low-topped
convection are expected to be positioned across the mouth of the
Mississippi at the start of the period (12Z). While the 40+ kt
southerly low-level jet, bisected by the stronger westerly mid-level
flow, will result in ample deep-layer shear for storm organization,
surface-based instability (500 J/kg MLCAPE at best) is expected to
remain well offshore, as will the risk for a damaging gust or
tornado. As such, a Marginal risk has been maintained south of the
Gulf shoreline.

By late evening, low 60s F dewpoints are expected to advect inland
along the western Florida coastline, contributing up to 500 J/kg
MLCAPE in spots despite poor low and mid-level lapse rates. Modest
veering in the sfc-850 mb layer ahead of the cold front suggests
that any of the more sustained storms may acquire brief instances of
rotation. As such, a Marginal risk has been introduced for the
possibility of a damaging gust or perhaps a brief tornado. However,
buoyancy quickly deteriorates with eastward extent, and storms are
expected to gradually weaken after 06Z per latest CAM guidance

..Squitieri/Darrow.. 01/07/2021

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