SPC Feb 12, 2019 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0655 AM CST Tue Feb 12 2019

Valid 121300Z - 131200Z


A few damaging wind gusts are possible from eastern Mississippi
across portions of Alabama and Georgia today, and a tornado cannot
be ruled out.

In a relatively progressive upper-tropospheric pattern, the main
perturbation affecting convective potential will be a synoptic
trough now located from the Dakotas southeastward over the OMA/MKC
areas, then southwestward over north-central/southwest TX.  Within
this trough, a strong northern-stream shortwave perturbation --
currently apparent in moisture-channel imagery over SD and eastern
NE -- should wrap through the trough and evolve into a closed 500-mb
cyclone over WI/IL by 00Z.  Meanwhile the more positively tilted
southern lobe will move eastward across the Mid-South and Arklatex
regions, reaching eastern portions of KY/TN, northern/central AL,
and southern MS.  By 12Z, the cyclone center should cross Georgian
Bay (Lake Huron), with the synoptic trough south-southwestward
across the southern Appalachians to the central Gulf. 

At the surface, 11Z analysis showed a low over northeastern IL with
cold front arching across western IN, southeastern MO, central AR,
western LA, and Gulf waters off TX.  A secondary/reinforcing
boundary was apparent from southwestern AR across central TX.  A
warm front was drawn from northeastern AL across southwestern GA and
northern FL.  The cold front should proceed eastward across the
Southeast through the period, preceded by a band of convection
currently evident from eastern TN across northern AL to southeastern
portions of MS/LA.

A band of convection, with isolated to widely scattered embedded,
episodic thunderstorms, is forecast to become better-defined over
the next few hours as it moves into a marginally destabilizing air
mass across portions of MS/AL.  For short-term potential, please
refer to SPC mesoscale discussion 99. 

As the main convective band progresses eastward over more of the
outlook area today, isolated damaging gusts, perhaps a severe gust,
are possible, and a tornado cannot be ruled out despite the weak
lapse rates and linear mode.  The destabilization will occur from a
mix of boundary-layer theta-e advection and subtle surface diabatic
heating beneath broken to overcast cloud cover.  MLCAPE near 500
J/kg should develop over parts of eastern/southeastern AL and
western GA.  The boundary-layer destabilization will be more
prevalent with southeastward extent over AL/western GA away from the
thickest clouds.  However, as the main low-level cyclone and
accompanying isallobaric forcing eject away from the area, low-level
lift and shear are each expected to weaken with time over the
regions experiencing greatest direct heating.  Deep shear and
low-level shear generally will remain favorable across the outlook
area until the line passes, though some veering of near-surface
winds will reduce bulk shear values with time ahead of the
convection -- especially the southern portion closest to the Gulf.

..Edwards/Gleason.. 02/12/2019

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