SPC Apr 23, 2017 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1235 AM CDT Sun Apr 23 2017

Valid 231200Z - 241200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF
THE SOUTHEAST...

...SUMMARY...
Scattered thunderstorms will develop across much of the Southeast
Sunday.  A few storms will produce gusty winds and hail.  Severe
threat may increase across eastern Georgia into South Carolina after
dark where one or two tornadoes could be observed.

...Southeast...

00z short-range model guidance is in good agreement regarding the
evolution of upper low as it progresses across the Mid-South into GA
by sunrise Monday morning.  Large-scale 12hr mid-level height falls
on the order of 90m will develop ahead of this feature as 70kt 500mb
speed max digs toward the FL Panhandle by 24/12z.  Associated
surface front is expected to extend from northwest GA into the FL
Panhandle at 18z...then advance into eastern GA during the overnight
hours.

Scattered thunderstorms may be ongoing along the frontal zone early
in the period across AL as high-level diffluent flow remains
supportive of deep convection.  However, strongest mid-level flow is
expected to lag the wind shift and forecast soundings do not exhibit
particularly strong shear or buoyancy early in the period.  While a
few storms may produce gusty winds or even marginally severe hail
during the morning hours it appears the most robust convection
should occur later in the afternoon, or during the overnight hours
when LLJ increases across SC.

Have opted to maintain MRGL threat for severe thunderstorms, both
for diurnally driven frontal convection during the day and for
overnight activity driven by low-level warm advection.  Forecast
soundings are not particularly unstable ahead of the front across
GA/northern FL during the day but deep southwesterly flow with
surface-6km bulk shear on the order of 35-40kt could support
organized storms.  Of more concern is the convection that will
evolve after dark across eastern GA/SC.  LLJ will increase markedly
after 00z and shear profiles become more supportive of organized
rotating updrafts.  If sufficient buoyancy can evolve across this
region severe probabilities will need to be adjusted to account for
overnight supercells capable of producing hail/damaging winds and
even tornadoes.  Later outlooks will address this threat and adjust
accordingly.

..Darrow/Leitman.. 04/23/2017

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