Area Forecast Discussion
Issued by NWS Shreveport, LA

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FXUS64 KSHV 200052
AFDSHV

Area Forecast Discussion
National Weather Service Shreveport LA
752 PM CDT Thu Apr 19 2018

.AVIATION...
For the 20/00Z TAF period, VFR conditions will prevail as high
clouds will gradually dissipate overnight with mostly SKC until
mid morning on Friday when additional cirrus will return. Winds
will continue from the NE overnight at less than 10 kts, becoming
more easterly on Friday with speeds increasing between 10-14 kts.

/19/

&&

.PREV DISCUSSION... /issued 317 PM CDT Thu Apr 19 2018/

DISCUSSION...
What a difference 24 hours can make as temps in the 60s late this
aftn is some 10 degrees below from what we experienced yesterday,
courtesy of yesterdays fropa which is now across the Gulf of Mexico.
The front also ushered in drier conditions with dewpoints only in
the 30s and 40s per 20Z metars. Concurrently, thin cirrus clouds
have moved across east TX late and this trend will likely continue
into tonight. As such, overnight temps may be hard-pressed to crater
given high-level cloudiness and have therefore elected to raise
temps a few degrees from the previous forecast package /40s/. In
addition to the cloud cover overnight, sfc ridging will commence to
slowly shift eastward away from the region which will cause sfc
winds to veer to the east-northeast by daybreak. Despite low-
amplitude UA ridging passing overhead, temps tomorrow will remain
below norm /upper 60s to lower 70s/, due to an upslope sfc regime
and increasing cloudiness.

The dry conditions will be short-lived as attention turns to the UA
low noted across ern CA/wrn NV late this aftn, progged to move east-
southeast across the Four-Corners region tomorrow aftn to across the
South Plains by Saturday morning. During this time, 500 mb height
falls will take place and sfc winds will be veering to the southeast
hence staring the transport of Gulf moisture. Best moisture axis
will initially be across portions of east TX and deep east TX
Saturday morning, whilst increasing large scale ascent takes place
ahead of the approaching disturbance. Majority of model solutions
agree that precip will affect the aforementioned areas late Saturday
morning/early aftn, and spread eastward throughout the day as a 50+
kt 500 mb jet max overspreads the area, in addition to an increasing
LLJ /30-40 kts/. Model solutions still differs a bit wrt to the
speed of the UA disturbance, as the NAM more or less /with the
exception of perhaps some lingering wrap around moisture/ has precip
clearing the region from west to east by late Sunday aftn versus the
slower ECMWF /Sunday night/. The GFS model for the last several days
has been the quickest solution by far but today`s model run is
pretty similar to that of the ECMWF. With that said, will likely
lean towards the latter solutions for this forecast package,
thereby exhibiting lingering wrap around moisture across the
eastern zones Sunday night/Monday morning. It is interesting to
note that the cold front associated with the disturbance will be
slow to shift southeastward across the region leading to a heavy
rainfall threat, particularly across portions of southwest AR,
northern, northeast and central LA. The Weather Prediction Center
projects 1-3 inches for this event, with the heaviest rainfall
affecting the said areas.

In addition to the heavy rainfall, the other question is will there
be a severe weather threat. There are a couple of things working
against a widespread severe weather threat: 1. The region enveloped
by mid-high level cloudiness will prevent substantial heating/mixing
2. The slow transport of Gulf moisture ahead of the front may result
in not a lot of moisture to work with and 3. MUCAPE values are being
progged in the 300-500 j/kg which is not overly substantial.
However, there is plenty of 0-6 km bulk shear /40-60 kts/ and if the
moisture return is quicker than anticipated and if there are some
breaks in the cloud cover to promote better daytime mixing, then
some storms approaching strong to severe levels can not be ruled out
/hail and damaging winds being the main threats/. Unfortunately, we
are going to have to wait and see how the synoptic and mesoscale
features play out.

Thereafter, dry northwest flow aloft will ensue on Tuesday with
daytime temps warming from the 60s to the 70s. Another cold front is
anticipated by mid to late week courtesy of a shortwave trough
passing to our north, though model solutions differ with the
strength of the frontogenetical forcing and hence whether or not
precip will develop along that front /GFS exhibits a relatively weak
front and therefore not a lot of precip versus the ECMWF stronger
front and hence better chances for precip/.

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  45  68  52  71 /   0   0  10  50
MLU  42  67  49  73 /   0   0  10  20
DEQ  40  66  49  66 /   0   0  10  80
TXK  43  65  49  67 /   0   0  10  70
ELD  39  67  49  71 /   0   0  10  30
TYR  47  67  52  67 /   0   0  10  90
GGG  44  68  51  68 /   0   0  10  80
LFK  47  69  54  71 /   0   0  10  60

&&

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

$$

19/29



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