Area Forecast Discussion
Issued by NWS Shreveport, LA

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FXUS64 KSHV 281048

Area Forecast Discussion
National Weather Service Shreveport LA
548 AM CDT Tue Mar 28 2017

The morning sfc analysis indicates a weak cold front extending from
Nrn MS SW along the AR/LA border to just N of SHV, to just S of
GGG/TYR, to near CRS and ACT. Very weak pressure rises noted on the
MSAS analysis is noted over Ern AR this morning, which may allow this
bndry to continue to nudge S a bit more to just N of MLU before
becoming stationary around/shortly after sunrise. However, this bndry
shouldn`t remain stationary long as Srly winds increase to its S,
allowing it to lift N to along the Red River Valley of SE OK/extreme
NE TX into SW AR by mid to late afternoon. Weak overrunning is ongoing
attm atop this bndry, which may allow for isolated convection to
develop (especially this afternoon) as diurnal heating results in
better instability. Have maintained slight chance pops today near and
S of the front, with much above normal temps again expected,
especially along/S of I-20.

The primary focus on this forecast though is the amplifying upper
trough noted on the water vapor loop now digging across Cntrl AZ,
which should close off later this morning as it traverses NM today and
into the TX/OK Panhandles Wednesday. Convection should begin to
develop later this morning over the Panhandle region, before
backbuilding S across W TX near/just E of the dryline. This convection
may organize into a squall line tonight as it progresses E, being
sustained by the 50kt Srly LLJ as it advects the warm/moist sector N
across much of OK into Ncntrl AR. The squall line should weaken late
though as it approaches Ecntrl TX/SE OK once it encounters weaker
instability and possibly outruns the deeper forcing ahead of the
closed low. With the progs slightly faster with the convection late
tonight, have increased pops a tad to mid and high chance across SE
OK/Wrn sections of E TX, with a few warm advection convection farther
E across the remainder of E TX/Wrn LA/SW AR.

While convection should remain ongoing Wednesday morning as it drifts
E into SE OK/E TX/Wrn AR near the residual dryline, the short term
progs remain in agreement with this convection intensifying by
afternoon as convective inhibition weakens and MLCape increases to
1500-2000+ J/kg given the warming temps near/lower to mid 80s. What
is interesting this morning are that the short term progs maintain
strong SErly low level winds across Extreme Ern TX across much of N
LA/SW AR Wednesday afternoon, with 0-1km SRH values of 300-400 m2/s2
over these areas. The split upper jet pattern rounding the based of
the closed low over over SE TX/NW Gulf will yield increasing vertical
motion atop this strong sheared environment, such that the threat for
bowing segments/lewps will develop with the likelihood of damaging
winds and isolated tornadoes. Given the relatively high wet bulb zero
heights and only elevated steep lapse rates, believe hail will be only
a marginal concern, with locally heavy rainfall possible where cells
develop/train over the same areas before beginning to shift E as the
closed low drifts E along the Red River. Have trimmed back pops a tad
Wednesday morning W of the I-49 corridor, before ramping pops up to
categorical/likely pops for the afternoon with mention of svr wording.
Continued with likely/categorical pops Wednesday evening with svr
wording before the convection diminishes from W to E late as dry air
entrains Ewd into the region.

The attendant weak cold front will slowly shift E across N LA/SW AR
Thursday, and will focus sct convection along and ahead of it with
what available moisture remains as the primary trough associated with
the closed low enhances large scale forcing over these areas. Could
see svr convection develop again where SBCapes climb to 1000-1500 J/kg
again during the morning/early afternoon, with instability further
enhanced by steep H850-700 lapse rates resulting in the potential for
hailers and damaging winds. Convection will diminish during the
afternoon with the passage of the cold front, with the wrap-around
cloud cover diminishing Thursday night as the low begins to open and
shift E away from the region.

Flat ridging aloft will quickly build over the Srn Plains/MS Valley
Friday in wake of this departing trough, and in advance of the next
closed low forecast to drop through the Srn Rockies. While a SErly low
level flow should return to the area Saturday, low level moisture
return will not return in earnest until Sunday, at which point
shortwave energy will begin to eject NE across the region ahead of the
low. Depending in the nwd expansion of the warm/moist sector, could
again be dealing with the prospects for svr convection Sunday
especially over E TX/N LA. Have maintained likely/high chance pops for
Sunday/Sunday night, with the potential for more sct convection Monday
as this low shifts E across the MS Valley.

Prelims to follow below...



SHV  83  67  83  63 /  20  20  70  80
MLU  82  64  85  66 /  20  10  20  80
DEQ  76  63  74  56 /  10  40  80  70
TXK  78  65  78  60 /  20  30  80  70
ELD  79  63  83  63 /  20  10  40  80
TYR  82  68  76  58 /  20  50  80  50
GGG  82  68  78  61 /  20  30  80  60
LFK  87  69  81  63 /  20  20  80  70




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