Area Forecast Discussion
Issued by NWS Shreveport, LA

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424
FXUS64 KSHV 221659
AFDSHV

Area Forecast Discussion
National Weather Service Shreveport LA
1059 AM CST Thu Feb 22 2018

.DISCUSSION...
Ongoing rain event continues to result in areas of flash flooding
this morning. Models continue to indicate a band of
heavy/training rainfall setting up this aftn/evening across the
I-30 and vicinity corridor. Have made some updates to PoPs based
upon current radar trends, but overall the PoP fcst looks to be on
track. For temps today, have updated with current obs, which are
trending quite a bit lower than previously fcst. Have made some
adjustments to max temps accordingly. /12/

&&

.PREV DISCUSSION... /issued 721 AM CST Thu Feb 22 2018/

AVIATION...
A warm frontal boundary just south of the cwa, will begin to surge
nwd, with scattered convection out ahead of this boundary crossing
the areal terminals along the I-20 corridor around 22/15z.
Scattered convection can be expected to continue, and possibly
widespread, especially further north at ktxk and keld later in
fcst period. NE winds becmg southerly as the warm front moves
north. Stgr capping inversion today at klfk which may see less
convection. Also, ifr conditions increasing north of convection
with cigs lifr and vsbys around 1/2 sm at ktyr and kggg in ne TX
and 1sm to 3sm elsewhere across the area. Low clouds and fog may
prevail again overnight towards the end of the fcst period. /07/

PREV DISCUSSION... /issued 431 AM CST Thu Feb 22 2018/

DISCUSSION...
.Although there has been a lull in widespread heavy rainfall
early this morning, this will be short-lived as wet conditions
make a return later today and into tonight...

UA troughiness continued to plagued the western CONUS early this
morning, thus resulting in persistent southwest flow aloft and
in the continual fetch of east Pacific moisture. At the sfc, the
cold front has become quasi-stationary from a Brownsville TX to a
Beaumont TX to a Jena LA line. The airmass is still relatively
moist behind this front and in fact, scattered showers and a few
thunderstorms noted from portions of deep east TX northeast to
across portions of northern LA and southwest AR early this morning
have ensued courtesy of ensuing low level moisture and a 30-40 kt
LLJ. This rainfall is falling atop of the heavy rainfall that
fell yesterday. Phone calls to emergency officials have reported
road closures that are still ongoing due to water covered roadways
such as Highway 83 between Pineland and Hemphill TX in Sabine
County. Elsewhere, some improvement has occurred /some roads that
were once impassable yesterday has now become passable/ but
dropping the Flash Flood Watch in effect for the entire FA is not
a very good idea given additional moderate to heavy rainfall is
poised to take place this afternoon-tonight.

A piece of energy ejected from the main parent trough across the
western CONUS will shift northeastward towards the Central Plains
late this aftn into tonight. Embedded impulses within the southwest
flow aloft coupled with the presence of a jet max at the 500 and 250
mb levels and enduring moisture, will result in the return of
moderate to possibly heavy rainfall across portions of east TX,
northeast TX, southeast OK and southwest AR this aftn. Heavy
rainfall will occur again tonight more or less across the same
areas /maybe stretching to across northwest LA/ but for this time-
frame it will be aided by the retreating warm front. Although a
lull in precip will take place this morning for some portions of
the ARKLATEX and more and more roadways become passable, that does
not mean the threat is over. With the return of rainfall this
aftn and again tonight, the saturated soils, poor drainage
roadways and low-lying areas that were once closed yesterday could
close again after this rainfall event. Rainfall totals of
1.00-2.00 inches may be possible across the northwestern-half of
the CWA and even though this is not overly significant, it will
likely not take much for flooding conditions to return given
yesterday heavy rainfall. As such, have elected to extend the
Flash Flood Watch through 12Z tonight for the entire CWA. As
trends are being watched, this watch could once again get extended
in time so make sure to stay alert to the latest weather
information.

Moderate to heavy rainfall will linger through Friday afternoon
across the northwestern-half of the CWA, but with a northern shift
thus coinciding with the retreating warm front. The Weather
Prediction Center now has an a moderate for Excessive Rainfall
during this time period across the said areas. The heavy precip
should shift north of the region by Friday evening/night. However
another UA shortwave across the western CONUS will shift
northeastward across the Central Plains and towards the Great
Lakes Region on Saturday, and will have an associated pacific
front /along with embedded impulses within the flow aloft/ that
will provide a focus for moderate to possibly heavy rainfall once
again across the northwestern-half of the CWA on Saturday.
Adequate MUCAPE does raise raise concern for some of the storms on
Saturday to become strong and possibly severe, with gusty winds
the main threat. However, the high helicity values does suggest
that some low level rotation will not be out of the question.

Thereafter, the pacific front will usher in a drier airmass /drier
than we have seen for some time/ across the region on Sunday,
resulting in precip coming to an end from northwest to southeast
across the the majority of the area. Could see some lingering
precip across the southern zones nearest to the best moisture
axis. Once again, an UA trough will impinge the western CONUS and
move eastward causing the sharpening of the southwest flow aloft
and with the return of a sfc southerly flow, the transport of Gulf
moisture will take place. Light rain showers and a few
thunderstorms will commence by Tuesday/Wednesday of next week, and
continue towards the end of the week until the aforementioned
disturbance shifts east of the region.

A temp gradient will set up across the FA today given the retreating
warm front /50s northwest to 70s southeast/, with a similar set
up tomorrow /60s northwest to 70s elsewhere/. The warmest day
looks to be on Saturday /70s/ as the warm front envelopes the
entire area, but thereafter temps will settle in around the 60s
given extensive cloud cover and chances of rainfall. /29/

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  59  58  74  64 /  70  90 100  40
MLU  67  63  78  63 / 100  30  60  30
DEQ  52  48  62  56 /  80 100 100  70
TXK  52  51  66  61 /  80 100 100  50
ELD  55  55  71  60 /  60  90 100  40
TYR  53  48  69  63 /  70 100 100  50
GGG  56  54  72  64 /  70 100 100  40
LFK  68  59  78  66 /  50  70  50  30

&&

.SHV WATCHES/WARNINGS/ADVISORIES...
AR...Flash Flood Watch through late tonight for ARZ050-051-059>061-
     070>073.

LA...Flash Flood Watch through late tonight for LAZ001>006-010>014-
     017>022.

OK...Flash Flood Watch through late tonight for OKZ077.

TX...Flash Flood Watch through late tonight for TXZ096-097-108>112-
     124>126-136>138-149>153-165>167.

&&

$$

12/07/29



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