Area Forecast Discussion
Issued by NWS Little Rock, AR

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FXUS64 KLZK 210251
AFDLZK

Area Forecast Discussion
National Weather Service Little Rock AR
951 PM CDT Mon Mar 20 2017

.UPDATE...
Temperatures remain warm this evening after several max
temperature records were tied or broken. Expect dry conditions for
most of the night tonight. However a cold front will approach
north Arkansas by morning and chances of showers will increase. As
temperatures climb and the atmosphere destabilizes during the day
Tuesday, chances for thunderstorms will increase in the north. The
threat for severe thunderstorms remains low at this time. Highs
will be in the lower 70s to mid 80s.

&&

.PREV DISCUSSION...(ISSUED 645 PM CDT Mon Mar 20 2017
)

AVIATION...
A cold front will approach Arkansas from the north tonight. This
front will enter north Arkansas around 12Z and slowly move south
Tuesday and exiting the south by 00Z Wednesdsay. This will bring a
few showers to the north during Tuesday afternoon. VFR conditions
are expected for most of the period, however MVFR conditions are
anticipated with the showers in the north.

PREV DISCUSSION...(ISSUED 303 PM CDT Mon Mar 20 2017
)

SHORT TERM...Tonight Through Wednesday
Through the day today, early morning clouds in southwest Arkansas
have scattered out with most locations in the state seeing mostly
Sunny skies. With strong southwest winds and good
mixing...temperatures have warmed significantly through the day
today with all locations in the state currently sitting at 80
degrees or higher.

Tonight, a cold front will approach the state from the north and
become parallel with flow aloft. This will allow the front to stall
in northern Arkansas which will bring a return of precipitation
chances to northern Arkansas Tonight and during the day on Tuesday.

On Wednesday...flow aloft will become more out of the NW and allow
the front to push to the south bringing rain chances to a greater
portion of Arkansas. Models, disagree on how far south the
precipitation will make it before the front once again
stalls...however do believe it is possible for precipitation chances
to expand to much of central portions of the state.

Front will once again stall to the south before lifting back to the
north in the long term.

LONG TERM...Wednesday Night Through Monday
Thursday...Models consistently show shortwave ridging building over
Arkansas during the day on Thursday. This is out ahead of a powerful
upper level trough that is expected to move over the southwestern
CONUS Wednesday night through Thursday. This trough will induce
strong cyclogenesis over the central and southern high plains
promoting the return of Wednesday`s frontal boundary north across
Arkansas as a warm front Thursday afternoon. The NAM indicates that
the warm front will get hung up in the Ozarks while the GFS and
ECMWF show the warm front lifting north into Missouri by Thursday
evening. Sided with the NAM for now...keeping high temperatures in
the mid 60s to the north...and closer to 80 across far southern
Arkansas. With upper level ridging in place expect mostly sunny
skies across the state.

Friday...The strong upper level trough over the southwestern CONUS
is expected to move northeast over the Texas panhandle and then east
along the Kansas/Oklahoma border throughout the day on Friday. This
strong upper level trough will spread strong large scale forcing for
ascent over the southern plains on Friday...likely resulting in a
line of strong thunderstorms developing along a dryline/Pacific type
cold front that is dynamically driven east towards Arkansas. The
organization and severity of this line of storms will largely depend
on the amount of destabilization out ahead of the approaching line
of storms. The line of storms is expected to approach Arkansas
during the late afternoon hours...so there is a decent chance that
the storms will be at their strongest when they approach the state.

That being said...models are not advertising a significant amount of
mixed layer CAPE out ahead of the approaching line of storms across
Arkansas Friday afternoon and evening. The model consensus shows
around 500-1000 J/kg of MLCAPE across Arkansas from 00 to 06Z
Saturday (Friday evening). If models are not underestimating
available potential energy for storms...then a strong squall line
producing scattered wind damage consistent with
microbursts/downbursts would be the most likely outcome. If
potential instability was being under represented by the
GFS/ECMWF... then more widespread wind damage would be possible. If
greater CAPE values are realized...the deep layer wind profile
associated with the line of convection is forecast to be largely
unidirectional out of the south. This shear profile combined with
the strong forcing for ascent from the upper trough and from the
pacific-type cold front would favor a line-echo wave pattern
configuration which could result in enough wind damage to be
considered a serial derecho. Large hail and isolated tornadoes would
also be possible...but appear to be significantly lower threats than
damaging "straight-line" winds in this type of convective mode.

The mesoscale details could change this forecast significantly of
course...but this far out the large scale environment does support a
strong squall line capable of producing damaging winds. Rain chances
appear to be very high with all of Arkansas likely to see at least a
quarter inch of rain. The only reason POPs are not 100 percent is
due to uncertainties with the exact timing of the squall line across
the state. It will rain...but exactly when showers and thunderstorms
move across the state is the biggest question for now.

Saturday and Sunday...The GFS and ECMWF differ a bit on how fast the
upper level low pressure system will move east over Arkansas and
Missouri on Saturday. The ECMWF is more progressive clearing the
upper low off to the northeast by Saturday afternoon. The GFS is
slower and lingers some rain shower chances over the state through
Saturday evening under the upper low. Sided with the GFS solution
for now...but may have to remove rain chances from the forecast if
it looks like the upper level storm system is moving faster than
forecast once it moves over the CONUS Wednesday night.

Sunday night - Monday...A strong shortwave trough is expected to
move over the plains and may bring another round of showers and
thunderstorms to Arkansas by Monday. Went with a slight chance of
thunderstorms at this time as confidence in the timing and placement
of a shortwave trough 7 days out is fairly low at this time. Both
the GFS and ECMWF advertise another strong upper level storm system
moving over the plains and towards Arkansas for the middle of next
week. It`s worth keeping an eye on...but is beyond the range of the
current forecast package.

&&

.LZK Watches/Warnings/Advisories...NONE.
&&

$$

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