SPC AC 022004

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0204 PM CST Mon Jan 02 2017

   Valid 022000Z - 031200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SOUTHEAST
   LOUISIANA...CENTRAL AND SOUTHERN MISSISSIPPI...SOUTHERN ALABAMA AND
   THE WESTERN FLORIDA PANHANDLE...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   ENHANCED RISK FROM THE CENTRAL GULF COAST STATES TO CENTRAL AND
   SOUTHERN GEORGIA...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS EXTENDING FROM
   PORTIONS OF THE MID SOUTH AND TENNESSEE TO SOUTHERN SOUTH
   CAROLINA...

   ...SUMMARY...
   Severe thunderstorms are expected through the afternoon and evening
   from eastern Louisiana across much of the central Gulf Coast States
   to portions of central and southern Georgia.  All severe hazards
   will be possible including damaging winds and tornadoes, especially
   across portions of southeast Louisiana and central and southern
   Mississippi through southern Alabama and the western Florida
   Panhandle.

   ...Lower MS Valley to central Gulf Coast States...
   Early afternoon radar imagery and lightning data showed a bowing
   line of storms moving into southwest MS and southeast LA, with a
   second area of thunderstorms located well east of the bowing line
   across southeast MS into the western FL Panhandle to central and
   eastern AL, and adjacent northwest GA.  The air mass across the
   Slight and Enhanced severe risk areas remains moderately unstable
   and sufficiently sheared for discrete rotating updrafts, primarily
   with storms across the warm sector.  Strengthening southerly
   low-level winds across much of the Enhanced risk area with an
   additional increase in midlevel flow (from the southwest to west)
   will maintain favorable effective srh of 200-400 m2/s2 for a
   continued tornado threat.  Meanwhile, WSR-88D VWPs indicated
   strengthening westerly inflow jet into the bowing line of storms,
   supportive of a continued likelihood for damaging winds from central
   and southern MS to southern AL this afternoon and evening.  The
   western extent of the severe probabilities and categorical risk
   areas have been trimmed east to account for the progressive eastward
   convective trends.

   The tornado probabilities have been reduced some across northern AL
   into TN, where storms should tend to remain elevated.

   ...Central and southern GA into southern SC...
   A destabilizing air mass along and south of the wedge front combined
   with strengthening southwesterly 500-mb flow, given the approach of
   the lower MS Valley shortwave trough suggests any storms developing
   within this region will have the potential to become severe.  Given
   these factors and model indication for storms in southern AL and the
   FL Panhandle to develop to the east-northeast into Georgia this
   evening, the severe probabilities and categorical Slight and
   Marginal risk areas have been expanded to the east.

   ..Peters.. 01/02/2017

   .PREV DISCUSSION... /ISSUED 1028 AM CST Mon Jan 02 2017/

   ...Gulf Coast states and Tennessee Valley...
   Considerable strong/severe convection is moving eastward across
   western Louisiana and extreme southeast Texas, in advance of a
   strong upper short-wave trough progressing eastward over central
   Texas.  Embedded within the cluster is a bowing line segment that
   has been producing occasional wind damage reports this morning.

   Additional storms are continuing downstream from this activity over
   eastern Mississippi and western/northern Alabama, in association
   with a weaker short-wave trough and within a coupled upper-level jet
   structure where divergence aloft is maximized.  This activity is
   resulting in widespread cloud cover that will likely limit diurnal
   heating and destabilization north of the I-20 corridor.  

   Surface analysis and visible satellite imagery indicate an east-west
   coastal warm front extending from southwest Louisiana into the
   northwest Florida, with richer low-level moisture /surface dew
   points around 70 degrees/ and warmer temperatures to the south of
   the front.  This boundary may lift farther north this afternoon but
   substantial progress inland will likely be impeded by ongoing
   convection and clouds. 

   Current indications are the eastward-moving QLCS over western
   Louisiana will progress across the lower Mississippi Valley this
   afternoon with a continuing threat for primarily damaging wind
   gusts.  Several tornadoes will also be possible, especially with any
   embedded rotational couplets that may develop and near the
   intersection of the advancing QLCS and the warm front.  In addition,
   any persistent semi-discrete cells developing downstream from the
   line may also pose a tornado threat given the clockwise-turning
   low-level hodographs evident in recent VAD profiles at LCH, LIX, and
   MOB radars.

   Other severe storms will be possible northward into parts of the
   Tennessee Valley where strong vertical shear may compensate for
   weaker instability.  A few damaging wind gusts and marginally severe
   hail will be the primary threats.

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