Day 1 Severe Weather Outlook

Valid 182000Z – 191200Z

…NO SEVERE THUNDERSTORM AREAS FORECAST…

…SUMMARY…
Some increase in thunderstorm activity is possible, particularly
near Texas and Louisiana coastal areas, late this afternoon and
evening. However, the risk for severe weather still appears
negligible.

…20Z Outlook Update…
The surface cold front continues to advance southeastward, into and
across the lower Mississippi Valley and Texas coastal plain, with
low-level moisture return ongoing, on south to southwesterly near
surface to 850 mb flow ahead it. Where surface dew points have
increased to roughly 65F , objective analysis suggests this has been
sufficient to contribute to weak boundary-layer CAPE on the order of
250-500 J/kg.

Along a northwest-southeast oriented zone ahead of the cold front
(roughly near/east of Greenville, Jackson and Biloxi MS as of 19Z),
this moisture is being lifted above a shallow, residual cooler/drier
and more stable surface-based air mass, which may continue to slowly
erode from west to east across Mississippi into Alabama this
afternoon. This likely will occur as the tail end (entrance region,
including 30-60 kt flow) of the pre-frontal 850 mb jet shifts from
central Mississippi/Alabama to the lee of the southern Appalachians
by early evening, coincident with the east-northeastward
acceleration of the primary short wave trough into/through the lower
Great Lakes/upper Ohio Valley.

Although some rotation has recently been evident in weak convection
near the effective warm frontal zone across south central
Mississippi, low-level hodographs characterized by larger size and
clockwise curvature are expected to remain largely confined to the
cool/stable side of this boundary, with generally negligible risk
for severe weather (see SWOMCD 63).

Otherwise, some increase in thunderstorm activity is ongoing across
Texas coastal areas into southwestern Louisiana, just ahead of the
cold front. Forcing for ascent associated with a low amplitude
perturbation crossing the lower Rio Grande Valley may be
contributing to this convection, which may persist and develop
eastward along coastal areas, in the presence of weak instability
and 30-35 kt westerly deep-layer ambient mean flow, through this
evening.

..Kerr.. 01/18/2020

.PREV DISCUSSION… /ISSUED 1026 AM CST Sat Jan 18 2020/

…Gulf Coast from Texas to Florida Panhandle…
A modest increase in thunderstorm coverage/intensity is expected
this afternoon, particularly near a cold front that will advance
southeastward across the ArkLaMiss and Texas Coastal Plain through
the afternoon. A couple of strong storms could occur, but
organized/sustained severe potential still appears low.

The cold front will intercept an increasingly moist boundary layer
across southeast/Deep South Texas, Louisiana into western/southern
Mississippi through the afternoon with middle/upper 60s F surface
dewpoints common. With the region well south of the polar jet/trough
over the Midwest and cloud cover tending to persist within the warm
sector, low/mid-level lapse rates will generally remain weak,
although somewhat stronger heating/destabilization may occur across
areas such as Deep South Texas. Overall, additional
warming/moistening could support a degree of updraft intensification
and somewhat more prevalent thunderstorms this afternoon mainly
across coastal Texas into Louisiana. However, the organized severe
potential near the cold front appears low given weakening deep-layer
winds and/or previously expressed thermodynamic limitations.

Farther east, a weak warm front will develop north-northeastward
through the afternoon and early evening into/across southern
Mississippi, southern Alabama and the western Florida Panhandle.
Convergence will likely remain weak near the warm front and upstream
surface wave/triple point, while destabilization will also be muted
by residual cloud cover and weak lapse rates. That said, hodographs
across this region, with their moderate curvature/length in the
lowest 1-2 km AGL, albeit with a flow weakness around 3 km, imply
some concern for brief updraft rotation/weak supercell
characteristics. Regardless, given only modestly conducive
thermodynamic factors, the overall organized severe potential still
appears limited and below outlook thresholds.

$$

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