Area Forecast Discussion
Issued by NWS Shreveport, LA

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027
FXUS64 KSHV 230323
AFDSHV

Area Forecast Discussion
National Weather Service Shreveport LA
1023 PM CDT Thu Apr 22 2021

.UPDATE...

Clouds continue to increase and thicken up this evening ahead of
our next big weather maker arriving on Friday. For the update this
evening, did make some slight upward adjustments to overnight low
temperatures based on current trends and with the increasing cloud
cover. Otherwise, expect some isolated showers possibly developing
after midnight across our western half and maybe expanding farther
east into North Louisiana and South Arkansas closer to daybreak.
Based on this thinking, the going PoP forecast was tweaked with
just slight chances mentioned across much of the region short of
our far eastern zones. No other changes are needed at this time.
Updated text products have already been issued.

/19/

&&

.PREV DISCUSSION... /issued 709 PM CDT Thu Apr 22 2021/

AVIATION...

For the 23/00Z TAF period, mid-level altocu continues to stream in
from the west across our airspace this evening with cigs starting
out around 10Kft. However, expect a gradual lowering of these cigs
as we move into the overnight hours with MVFR conditions expected
to overtake all sites through early to mid morning on Friday. By
this time on Friday, a retreating warm front will also be lifting
northward across the region with scattered showers developing and
spreading NE through late morning into the afternoon with embedded
thunderstorms also becoming more likely. As a result, expect cigs
and vsbys to drop into the IFR range as we move through the latter
half of the TAF period on Friday. Winds will continue to trend SE
with speeds increasing to between 10-15 kts on Friday along with
some higher gusts near 20 kts with convection by Friday afternoon.

/19/

PREV DISCUSSION... /issued 308 PM CDT Thu Apr 22 2021/

SHORT TERM.../Tonight through Saturday/

The quiet period of weather we`ve been experiencing is about to
end, as shower and thunderstorm chances begin to increase tonight
ahead of the next big system. The Slight risk for severe weather
that was in place remains relatively unchanged, as does the
overall setup.

Across central Texas, a dryline will set the stage for some of the
first rounds of severe weather. In our area however, the severe
threat continues to rely on that northward pulling warm front and
surface low pressure. Along the warm front, storms appear to be
mostly elevated, but given steep low-level lapse rates, these
storms may produce large hail. Damaging winds will also be
possible, as the multicell structure and favorable DCAPE values
will also support that threat. The one wild card in this event is
the tornado threat, and the one I want to camp on the most. While
storm mode is expected to be very sloppy, low level wind shear
values are rather impressive. This will only amplify as the
surface low inches closer to the Four-States region. On top of
that, forecast hodographs show plenty of veering off the surface,
which would allow for storms to rotate. As is the case with any
event with messy storm mode, there will be fighting between cells
to see if any of them can take advantage of this environment. In
the event storms remain more isolated for an extended period of
time, the greater the tornado threat will be. However, this does
not mean tornadoes can be ruled out entirely, even with the
aforementioned messy storm mode. All this to say, it looks like
clusters of strong to severe thunderstorms will form and move
across the Four-States region by Friday evening, and possible into
the overnight hours.

On top of the severe weather, locally heavy rainfall may be
possible, and very heavy rainfall rates appear likely for brief
periods of time. We are anticipating widespread QPF values of an
inch, with 2-3 inch pockets of QPF possible in our southern zones.
A Flash Flood Watch was considered with this forecast package, but
decided against given current system progression. However, one may
be issued later in the event the system slows, or QPF values
increase. Isolated flash flooding in general can not be ruled out
in poor drainage areas, or other areas prone to flash flooding
during heavy rainfall events.

Temperatures over the course of this short-term will run about
seasonal for tonight and tomorrow, before warming up to slightly
above seasonal for tomorrow night and Saturday. This will be in
part due to the warm front pulling north with the associated
severe weather.

/44/

LONG TERM.../Saturday Night through Wednesday Night/

High pressure under nwly flow aloft will set up across the region
Saturday night in the wake of the cold front/upper trof passage of
Friday/Saturday. Upper ridge axis to our w will drift ewd Sunday and
Monday across our region, with sly sfc winds returning, resulting in
mostly clear skies and warm temps topping out in the mid 80s by
Monday.

However, upper flow will transition to swly Monday night into
Tuesday, as the upper ridge axis departs to the e and our next trof
digs sewd. Models continue to differ with respect to timing and
other details as this trof approaches our region during the Tuesday
night/Wednesday timeframe. The GFS by far remains the fastest with
the passage of the trof/cold front, with the Euro lagging behind and
more positively tilted with trof. The CMC is even slower, keeping
the positive tilt to the trof, similar to the Euro, as it moves
across our area. With such significant discrepancies, it seemed
prudent to continue to hold close to NBM PoP values, keeping them
cut off just below the "likely" threshold. With regard to a severe
weather threat, it does certainly seem possible, especially if the
GFS`s more aggressive, neutral to slightly negative tilt solution
verifies. However, details with respect to threats and timing are
simply just not clear attm, and we will continue to monitor trends
over the next few days in hopes that these solutions come into
better agreement.

/12/

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  58  74  64  79 /  20  80  90   0
MLU  54  72  63  81 /  10  60 100  10
DEQ  53  67  58  75 /  20 100  90  10
TXK  54  69  62  75 /  20  90  90  10
ELD  55  69  58  78 /  20  80 100  10
TYR  59  74  62  76 /  20  90  70   0
GGG  58  73  63  76 /  20  90  90   0
LFK  61  76  66  80 /  20  90  80   0

&&

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

$$

19/44/12



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