SPC Aug 27, 2017 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1257 AM CDT Sun Aug 27 2017

Valid 271200Z - 281200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
SOUTHEAST TEXAS INTO SOUTHWEST LOUISIANA...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MIDDLE TO UPPER TEXAS COASTAL PLAIN AND LOUISIANA...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN AND CENTRAL PLAINS INTO THE LOWER MISSOURI VALLEY...

...SUMMARY...
A few tornadoes are expected today into tonight across the upper
Texas coastal plain eastward into southwest Louisiana. Isolated
strong to severe storms will also be possible this afternoon and
evening from the northeastern Texas Panhandle northeastward into
north-central Missouri.

...Southeast Texas/Southwest Louisiana...
The National Hurricane Center keeps Tropical Storm Harvey nearly
stationary across the middle Texas coastal plain today and weakens
Harvey to a Tropical Depression. Rainbands should continue to
develop northeast of Harvey's center across southeast Texas and
southwest Louisiana. Moderate instability is forecast to remain in
place along the southeast Texas coast with instability maximized in
the Houston/Galveston vicinity. Forecast soundings for today at
Houston and Galveston maintain moderate deep-layer shear throughout
the day. Wind profiles also have strong directional shear in the
low-levels with 0-3 storm relative helicities remaining in the 350
to 450 m2/s2 range. This will continue to be favorable for
supercells and tornadoes within the bands with the heaviest
rainfall. The tornado threat should be greatest with cells that
remain discrete about 150 statute miles to the east-northeast of
Harvey's center today and tonight.

...Southern and Central Plains/Lower Missouri Valley...
An upper-level trough is forecast to move southeastward across the
mid Missouri Valley today. The southwestern extension of the
shortwave trough is forecast to be in the central Plains. At the
surface, a cold front will move southeastward across north-central
Missouri with the front extending southwestward into Kansas.
Convection may be ongoing along the front this morning. Outflow from
this convection should be important to where thunderstorm
development occurs later in the day. Model forecasts suggest that a
corridor of moderate instability will develop by afternoon from
southern Kansas northeastward into northwest Missouri where MLCAPE
values could reach the 1500 to 2000 J/kg range. This combined with
0-6 km shear in the 25 to 35 kt range along with steep low-level
lapse rates may be enough for a marginal wind-damage threat during
the mid to late afternoon. Hail will be possible with the stronger
updrafts, especially from the northern Texas Panhandle
east-northeastward into southern Kansas, where mid-level lapse rates
are forecast to be steepest.

..Broyles/Jirak.. 08/27/2017

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