#673 Postby 869MB » Sat Apr 13, 2019 1:09 am
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1248 AM CDT Sat Apr 13 2019
Valid 131200Z - 141200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
FAR EAST TEXAS...LOUISIANA...FAR SOUTHEAST ARKANSAS AND WEST-CENTRAL
MISSISSIPPI...
...SUMMARY...
Numerous severe thunderstorms capable of producing tornadoes, wind
damage and large hail, are expected across parts of east Texas,
Louisiana, southern Arkansas, Mississippi, western Alabama and
surrounding areas today and tonight.
...East Texas/Louisiana/Southern Arkansas/Mississippi/Western
Alabama...
A vigorous upper-level trough will move across the southern Plains
today as a mid-level jet rounds the base of the system. At the
surface, a low will move into the Arklatex with a moist airmass in
place to the southeast of the low across east Texas, Louisiana and
western Mississippi. Surface dewpoints in the moist sector should be
in the upper 60s and lower 70s F by late morning. Thunderstorms
should be ongoing across north-central into northeast Texas at the
start of the period. This convection with a hail threat, is likely
to move into the Arklatex by midday. Further south across southeast
Texas into Louisiana, the airmass should become moderately unstable
and remain primarily undisturbed. In response to the approach of the
upper-level trough, a low-level jet is forecast to move into far
eastern Texas and western Louisiana during the early afternoon.
Thunderstorms should initiate to the northwest of the low-level jet
on the northern edge of the stronger instability. Strong deep-layer
shear profiles will favor supercell development. Supercells will
have a potential for large hail in the early afternoon. The more
dominant storms could produce 2-inch diameter hailstones. As the
upper-level trough approaches and the exit region of a progressive
mid-level jet moves into southeast Texas during the early afternoon,
surface-based thunderstorms should rapidly initiate and move
eastward into western Louisiana.
RAP forecast soundings across the moist sector at 21Z from Monroe,
LA southward to Alexandria, LA show MLCAPE values in the 2000 to
2500 J/kg range. Deep-layer shear is forecast to steadily increase
due the approach of the mid-level jet with forecast soundings
showing 0-6 km shear of 50 to 60 kt by late afternoon. This combined
with strong low-level shear will be favorable for supercells and
tornadoes across the moderate risk area. 0-3 km storm-relative
helicities are forecast to be in the 350 to 450 m2/s2 range
supporting strong tornadoes with the more dominant supercells near
the axis of the low-level jet. A potential for long-track tornadoes
will be possible and a regional outbreak of tornadoes could occur
across parts of the moderate risk area. By early evening, the
cluster of severe storms is forecast to move into southwestern and
central Mississippi where a potential for strong tornadoes will
continue. However, the wind-damage threat may become the more
dominant hazard as the convection moves further to the east where
instability is forecast to be weaker.
...Northern South Carolina/Central and Eastern North Carolina/Far
Southeast Virginia...
Southwest mid-level flow will be in place across the East Coast
today. At the surface, a moist airmass will exist across the
Atlantic Coastal plains where dewpoints should be in the upper 60s
and lower 70s F. As surface temperatures warm across the moist
airmass, pockets of moderate instability may develop from northern
South Carolina northeastward into eastern North Carolina.
Thunderstorms are forecast to initiate in the foothills of the
Appalachians and move eastward into the stronger instability during
the afternoon. SBCAPE values around 1000 J/kg evident on RAP
forecast soundings, along with 30 to 40 kt of 0-6 km shear should be
enough for a marginal severe threat. Strong wind gusts and hail will
the primary threats.
..Broyles/Bentley.. 04/13/2019
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