- Day Three
acus01 kwns 140601
Storm Prediction Center ac 140600
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
1200 am CST Fri Dec 14 2018
Valid 141200z - 151200z
..there is a slight risk of severe thunderstorms across portions of
northern/central Florida and far southeastern Georgia...
Isolated severe thunderstorms will be possible from northern/central
Florida into southeastern Georgia and the coastal Carolinas today
into tonight. Strong to locally damaging winds should be the main
An upper low centered over East Texas will move northeastward to the Tennessee
Valley through the period. A related strong 80-100+ kt
mid/upper-level jet will overspread much of the southeast later
today. A 40-50 kt southerly low-level jet initially over the Florida
Panhandle should shift eastward over northern Florida into southeastern
Georgia and the eastern Carolinas, which will bring increasing low-level
moisture to these areas through the day. At the surface, an occluded
low will develop northeastward to the Tennessee Valley in tandem with the
upper low while continuing to slowly weaken. A secondary surface low
should form near the Florida Panhandle by this evening and then track
northeastward along a coastal front across the eastern Carolinas
through the end of the period.
..northern/central Florida into southeastern Georgia...
A pre-frontal line of thunderstorms will likely be ongoing at the
start of the period over the eastern Gulf of Mexico and perhaps
extending into parts of the Florida Panhandle. The airmass ahead of these
storms across northern/should slowly destabilize as the previously
mentioned low-level jet brings an airmass characterized by mid to
upper 60s surface dewpoints northward. Even so, limited diurnal
heating owing to widespread cloudiness and weak mid-level lapse
rates should temper instability late this morning into the
afternoon, with MLCAPE of 500-1000 j/kg probable. Deep-layer shear
will increase to around 35-45 kt across this region by the
afternoon, which will support continued organization of the
convective line as it moves eastward across the northern/central Florida
Peninsula. Isolated strong to damaging winds will likely be the
primary threat given the linear storm Mode. A tornado or two may
also occur with circulations embedded within the line as strong flow
in the 0-3 km layer supports enlarged low-level hodographs.
Strengthening southerly low-level winds by this evening will
transport greater low-level moisture over the coastal Carolinas,
with the potential for near-surface-based thunderstorms likewise
increasing as surface dewpoints reach into the mid to perhaps upper
60s. Some threat for isolated strong/gusty winds and perhaps a
tornado may exist tonight into early Saturday morning, mainly
along/near the coast associated with the low-level jet and increased
low-level shear. A relatively greater potential for surface-based
thunderstorms may exist across far eastern NC the last few hours of
the period (08-12z), with some model guidance showing greater
instability across this region. Uncertainty regarding storm coverage
and the realization of this instability limits confidence in any
more than marginal probabilities for severe thunderstorms at this
..mid-south into MS/al...
Cold mid-level temperatures and residual moisture wrapping around
the upper low should act to increase elevated instability over the
mid-south and vicinity today. Isolated to perhaps widely scattered
thunderstorms should be ongoing this morning across northern la into
southern AR, with additional activity developing later this
afternoon across western Tennessee/Kentucky and northern MS. Forecast soundings
show wind profiles will likely not be favorable for organized severe
thunderstorms. But, some storms could produce small hail owing to
steep mid-level lapse rates.
Farther east into al, stronger mid/upper-level winds are forecast
this afternoon, and a pocket of weak instability (mlcape around 500
j/kg) should develop amidst surface dewpoints in the upper 50s/lower
60s ahead of a cold front. The forecast environment would
conditionally support at least some severe potential, but convective
coverage will likely remain sparse owing to the filling upper low
and weakening surface low. Have not included marginal probabilities
due to uncertainty regarding storm initiation/coverage.
acus11 kwns 140012
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 140012
Mesoscale discussion 1708
National Weather Service Storm Prediction Center Norman OK
0612 PM CST Thu Dec 13 2018
Areas affected...the barrier islands of southern Alabama and near the
Concerning...severe potential...watch unlikely
Valid 140012z - 140115z
Probability of watch issuance...5 percent
Summary...several weak supercells will approach the barrier islands
south of Mobile Bay and near the Florida/Alabama border. Cool/stable
conditions in the low levels will limit the brief/weak tornado risk.
Discussion...recent surface analysis places a warm front roughly 40
nm south of Alabama barrier islands. Conditions south of the warm front
are hospitable to weak surface-based cape (200-500 j/kg) whereas
north of the boundary SBCAPE is nil. The kmob VAD shows a strongly
veering wind profile supporting storm rotation. Several updrafts in
the shelf waters south of the Alabama coast have acquired supercell
rotation during the past 1-2 hours.
The warm front is forecast to very slowly advance north during the
evening and approach the coast. As a result, a couple of weak
mesocyclones may move towards or affect the immediate coast.
However, given the poor low-level lapse rates acting as a limiting
factor, it seems unlikely a brief/weak tornado would move onshore.
The immediate coastal areas of Alabama and the western Florida Panhandle will
continue to be monitored.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 29918834 30248807 30398710 29978700 29918834