SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1250 AM CDT Sun Oct 18 2020

Valid 181200Z - 191200Z


Severe thunderstorms are not expected across the country.

...Eastern OK to Southern IN...

Broad mid-level cyclonic flow is forecast to continue across the
northern two-thirds of the CONUS during the day1 period. Within this
flow regime, several notable short-wave troughs are expected to
translate across the northern tier of States before ejecting through
the Great Lakes. As a result, the primary corridor for meaningful
large-scale forcing for ascent should be noted ahead of these
features. The main area where convection seems likely will be across
the Ozark Plateau region into the lower OH Valley. While the
aforementioned storm track will be just north of this corridor,
veered LLJ from north TX into KY should aid moistening atop the
boundary layer within a warm-advection regime. Latest model guidance
continues to suggest buoyancy will increase from northeast
TX-AR-lower OH Valley, but a notable warm layer near 700mb, and
marginally steep mid-level lapse rates, should limit instability.
Forecast soundings suggest MUCAPE between 500-800 J/kg will be
common where elevated convection is expected to develop, primarily
during the latter half of the period. Local hail algorithms suggest
any hail that generates within this convection should be mostly
sub-severe. For these reasons have lowered the severe threat to less
than 5 percent.

...South FL...

Deep easterly flow along the southern periphery of an elongated
upper ridge will maintain moist profiles across south FL. Forecast
soundings exhibit high-PW air mass with poor lapse rates, but modest
flow for westward-moving convection. Latest satellite imagery/model
data suggest a weak mid-level disturbance will approach the FL
Atlantic coast later this morning. This feature should encourage
scattered convection that will track west toward the Gulf Coast
during the afternoon.

..Darrow/Lyons.. 10/18/2020

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