Area Forecast Discussion
Issued by NWS Shreveport, LA

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FXUS64 KSHV 131711 AAA
AFDSHV

Area Forecast Discussion...UPDATED
National Weather Service Shreveport LA
1211 PM CDT Tue Apr 13 2021

.UPDATE...
A surface low is located between Texarkana and Shreveport. A
quasi-stationary front extends eastward from the low, and a cold
front trails southwest from the low to south of Carthage, to near
Jacksonville. A sharp temperature gradient exists along the
frontal boundary. Temperatures behind the cold front are only in
the lower to mid 70s. In the warm sector, despite abundant cloud
cover, temps have already warmed into the lower 80s, which was
very near forecasted highs. In addition, a few thunderstorms have
affected La Salle and Grant Parishes resulting in some slightly
cooler temperatures, but there is little in the way of upstream
development at this time. Therefore, based on latest obs, high
temperatures were raised by a few degrees in most areas,
especially in the warm sector south of the frontal boundary.

Additional showers and thunderstorms are still expected to develop
across the southern half of the forecast area in the warm sector
later this afternoon, especially with some more diurnal
instability in place. Therefore, PoPs were left intact for the
remainder of today.

Updated text products have already been sent.

CN

&&

.PREV DISCUSSION... /issued 637 AM CDT Tue Apr 13 2021/

AVIATION...
VFR conditions should persist across much of the region through
the day and evening, although MVFR cigs have developed across
portions of Deep E TX and WCntrl LA, which may spread N and
briefly affect the TYR/GGG terminals through late morning. Cu cigs
should develop farther N and E across the I-20 corridor of N LA
through midday, and eventually into SW AR during the afternoon, N
of a warm front that will slowly lift N into E TX/NCntrl LA. Sct
convection is expected to develop late this morning through the
afternoon near this bndry over Deep E TX/NCntrl LA, and may affect
LFK/MLU by mid/late afternoon. Have added VCTS mention here, with
this convection expected to diminish by early evening with the
loss of heating. MVFR cigs should develop this evening S of the
warm front and spread N atop a shallow cold front which will begin
to slowly drift S across E TX/N LA late this evening/overnight,
with sct convection developing over E TX/SE OK and spreading E
across the region after 06Z. Have added VCTS mention to all
terminals late tonight, with cigs expected to become low
MVFR/possibly IFR with vsby reductions possible in the TSRA. The
convection will diminish from W to E by mid-morning Wednesday,
although IFR/MVFR cigs will persist through much of the day even
in wake of the weak cold fropa during the morning. Lt S or Lt/Vrb
winds this morning will become light NE with the cold fropa
across NE TX/SW AR by mid to late morning, but remain Lt SSE
across Deep E TX/N LA. /15/

PREV DISCUSSION... /issued 412 AM CDT Tue Apr 13 2021/

SHORT TERM.../Today through Wednesday/

The morning sfc analysis indicates that our weak/shallow cold
front has begin to slip SE through McCurtain County OK and into
portions of extreme NE TX, from near a LBR to W of a OSA/JDD to
CRS line as of 0830Z. Sct elevated convection continues to develop
W of the frontal bndry across portions of N TX near and just ahead
of the H850 front and leading edge of the deeper H850 moisture,
along a subtle shortwave impulse traversing the mainly zonal flow.
MUCapes are analyzed to be in excess of 1000 J/Kg over this area
within a region of steep mid level lapse rates, with the
expectation that the convection will weaken as it spreads ENE into
NE TX later this morning where a drier and more stable air mass
resides just N of the advancing H850 moisture lyr.

The cold front remains progged to continue drifting SSE into E TX
and the Nrn sections of SW AR today before temporarily becoming
stationary with the onset of deeper mixing, with the H925-850
moisture noted on the RGB satellite imagery expected to continue
spreading NNE into much of E TX/N LA this morning, with the
elevated cu field eventually spreading into the remainder of the
region during the afternoon. Isolated -SHRA will be possible this
morning farther S over portions of Deep E TX into Cntrl LA along a
warm front, with the warm/moist sector expanding farther N into
Lower E TX/N LA during the day S of the stalling cold front. The
CAMs and some of the global models continue to suggest sct
convection developing during the afternoon especially from SE TX
into Cntrl and Srn LA near the warm front and expansive moist
sector, possibly enhanced by the weak shortwave energy now over
NCntrl TX. Have maintained likely pops for the far SE zones, while
expanding the mid/high chance pops into portions of Deep E
TX/NCntrl LA, which should diminish some during the evening with
the loss of diurnal heating. Isolated severe convection can not be
ruled out this afternoon over the Srn zones where moderate MLCapes
develop, further enhanced by steep mid level lapse rates in excess
of 7C/km, although the bulk of this threat should remain farther S
of the region over S LA. Mixing should be sufficient enough this
afternoon for above normal temps to continue near and S of the
front, before pressure rises build S into the area overnight from
the Cntrl Plains, thus nudging the cold front back S into E TX/N
LA.

The progs do suggest that weak shortwave energy over the Desert SW
this morning will lift NE through NW TX this afternoon before
traversing OK/the Red River Valley tonight, with increasing
overrunning and increasing PVA atop the shallow cool air dome
resulting in an increase in elevated convection late this evening
and overnight. Have increased pops to high end likelies areawide
late, with steep mid level lapse rates persisting over much of the
area in a zone of increasing bulk shear suggesting that some
organized svr potential will exist with the threat of large hail,
and possibly damaging winds should these storms be able to root
down to the sfc. Any svr threat should diminish after daybreak
Wednesday as the overrunning gradually weakens once the shortwave
exits the region to the E. Did maintain likely pops though during
the morning over the Ern half of the area, before the attendant
H850 trough begins to build S through E TX/N LA. Did keep slight
and low chance pops going though for the afternoon for portions
of Deep E TX/Srn and Ern sections of NCntrl LA just ahead of the
trough where the leading edge of the shallow cold front will
reside and could temporarily stall again with mixing, before we
await the next shortwave trough which should result in an increase
in sct elevated convection once again Wednesday night. Should
finally begin to see some of the cooler conditions advecting S
into the area in wake of the front late tonight, with below normal
temps expected over much of the area Wednesday.

15

LONG TERM.../Wednesday Night through Monday/

A weak Omega Block pattern across the Upper CONUS and southern
Canada maintains zonal flow across the southern CONUS as the long
term period begins. This zonal flow also maintains the advection of
Pacific moisture aloft and across Texas into our area through the
rest of the week into the weekend. At the surface, the cold front
that passes through Louisiana on Tuesday will become quasi-
stationary along the Gulf Coast through the weekend. This setup at
the surface provides an additional focus for moisture with multiple
shortwaves propagating across Texas into the Ark-La-Tex.

By Thursday, a lull between the shortwaves arrives, allowing
afternoon highs to just reach the 70s, while the next more vigorous
shortwave is on the way across the Four Corners. Simultaneously
aloft, the aforementioned Omega Block pattern will be displaced by a
stronger Rex Block further upstream. As the eastern trough of that
blocking pattern shifts further east into the Great Plains, the
subtropical jet streak shifts further east, enhancing divergence for
Friday`s shortwave. While the best divergence may remain to our
north, precipitation chances still remain elevated area wide
throughout Friday. That shortwave finally exits the area by Saturday
night, with drier conditions returning and our zonal flow becoming
southwesterly flow. On Sunday, high pressure builds in and afternoon
highs return to the 70s once again as cloudy skies thin out by the
beginning of next week.

With this active weather pattern occurring through this weekend,
cloudy skies and subsequently below average temperatures will also
be maintained through this weekend into early next week. Overall,
WPC QPF Day 1 through 7 values amount to just over an inch area wide
and closer to two inches in our southern zones. /16/

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  83  60  68  53 /  20  70  60  40
MLU  81  60  68  53 /  40  70  80  30
DEQ  78  53  63  49 /  20  70  30  30
TXK  80  56  63  51 /  20  70  50  30
ELD  81  55  64  48 /  10  70  70  20
TYR  81  60  69  54 /  20  70  40  40
GGG  81  60  68  52 /  20  70  50  40
LFK  81  66  76  56 /  40  70  60  50

&&

.SHV WATCHES/WARNINGS/ADVISORIES...
AR...None.
LA...None.
OK...None.
TX...None.
&&

$$

09/19


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