SPC AC 310825
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0225 AM CST Sat Dec 31 2016
Valid 021200Z - 031200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS MONDAY ACROSS
PARTS OF SOUTHEAST TEXAS THROUGH MUCH OF LOUISIANA AND
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS
SURROUNDING PORTIONS OF THE WESTERN INTO CENTRAL GULF COAST STATES
AND ADJACENT PORTIONS OF THE MID SOUTH...
Severe storms are possible Monday across parts of the western into
central Gulf Coast states.
A blocking mid/upper high, centered near the Gulf of Alaska, appears
likely to remain prominent through this forecast period. Downstream
troughing over the northwestern U.S. may undergo considerable
deformation, with at least one significant impulse forecast to
emerge from it, and accelerate east northeastward toward the upper
Great Lakes region.
In lower latitudes, subtropical ridging may elongate east to west,
with its center of highest heights shifting from the Caribbean into
southern Mexico. On the northern periphery of this feature, into
larger-scale ridging over the southeastern U.S., models generally
indicate significant weakening of a remnant impulse accelerating
east northeast of the southern Plains.
In lower levels, while a significant cold intrusion progresses to
the lee of the northern Rockies, primary surface low development
appears likely to remain well north of the Gulf Coast region, from
parts of the central Plains into portions of the Upper Midwest/Great
Lakes region. However, it appears that a secondary surface low
could accompany the southern mid-level impulse, redeveloping
eastward/northeastward out of Texas.
While a moist return flow off the Gulf of Mexico may support
substantive boundary layer destabilization inland of northwestern
and north central Gulf coastal areas by 12Z Monday, guidance is
suggestive that this air mass may be overturned, and return flow
cut-off, in the wake of considerable convective development expected
to spread out of Texas early in the period. It is possible, though,
that an appreciable risk for severe weather may continue across the
central Gulf states through the day Monday.
...western into central Gulf Coast states...
Variability exists among the model output concerning just how fast
forcing for ascent, associated with the impulse emerging from the
southern Plains, will become displaced from the stronger boundary
layer instability and weaken during the day Monday. However, an
organized mesoscale convective system may be ongoing at 12Z Monday
across parts of east/southeast Texas. Aided by a continuing inflow
of weak to moderately unstable air (probably characterized by CAPE
in excess of 1000 J/kg), in the presence of sufficiently strong deep
layer shear, it appears possible that activity could maintain
significant strength through much of the day Monday, before
overturning the better boundary layer instability and cutting of the
richer return flow.
Until convection weakens, it may continue to support the risk for
potentially damaging surface gusts. Clockwise curved low-level
hodographs may also be large enough to support potential for
tornadoes, particularly with any discrete storms which may form near
or just ahead of the convective system as it spreads across the
central Gulf States/lower Mississippi Valley.
CLICK TO GET WUUS03 PTSDY3 PRODUCT
NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0830Z