Area Forecast Discussion
Issued by NWS Little Rock, AR

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FXUS64 KLZK 121749
AFDLZK

Area Forecast Discussion
National Weather Service Little Rock AR
1149 AM CST Sun Nov 12 2017

.AVIATION...12/18Z TAF CYCLE

Band of mostly -RA wl cont to shift EWD acrs SRN AR early aftn.
Meanwhile, weak CDFNT over NRN AR wl work SWD thru early tngt.
VFR conds wl prevail ovr the SRN half of the FA into tngt, with
MVFR conds expected late tngt into Mon mrng. Post-fntl clouds wl
work SWD into NRN AR this aftn, with MVFR conds prevailing thru
much of the PD. Winds wl be light and variable. /44/
&&

.PREV DISCUSSION...(ISSUED 400 AM CST Sun Nov 12 2017)

SHORT TERM...Today Through Tuesday
The flow aloft will remain nearly zonal north of a ridge of
high pressure over Mexico. A minor ripple/shortwave in the
flow will pass to the north of Arkansas today. At the surface,
a weak cold front will push through the region from Missouri.

While there will be a lot of clouds surrounding the front,
overall moisture will be lacking. Spotty light rain is in
the forecast, with amounts less than a tenth of an inch.

Clouds will decrease from the north tonight as a large area
of high pressure builds behind the front. However, the front
will not be followed by much in the way of cold air, with
little fluctuation in temperature despite a frontal passage.

Dry weather is expected on Monday, and there will be more
sunshine. Even so, the aforementioned high will exit toward
the Ohio Valley, and clouds will begin increasing from the
west during the day.

As surface winds turn from northeast to southeast, and moisture
levels go up, a few showers will be possible north/west of Little
Rock Monday night/Tuesday.

As far as temperatures, daytime readings will be mostly below
average, with closer to average readings at night. (46)

LONG TERM...Tuesday Night Through Saturday
Perpetual Rex block across western Mexico remains a dominant upper
level feature through the entire period with initially zonal flow
aloft over the forecast area. At the surface, high pressure draped
across the eastern U.S. will gradually compress as an upper
disturbance and associated surface cold front move east, allowing
southerly return flow to develop across the southern states by
Tuesday night into Wednesday.

Our first system will approach from the north by Wednesday morning
as an upper shortwave trough pushes through the Great Lakes and a
cold front moves south out of the central Plains. Since the parent
upper trough will be well northeast of the area, upper support will
be marginal, but enough forcing within a modest plume of deep
moisture ahead of the cold front should generate scattered showers.
Current guidance suggests some instability will be present, so
included a mention of isolated thunder. The front washes out by
Thursday morning and lifts back north as a weak frontal wave
develops across OK. Scattered showers will persist as the boundary
lingers near the area.

Attention then focuses on the development of a high-amplitude trough
late in the week. As this feature ejects across the northern and
central Plains, deep surface cyclogenesis invof the Great Lakes is
expected with a stronger cold front sweeping across the eastern U.S.
by next weekend. Ahead of the front, strong southwesterly flow is
expected, although significant and sustained moisture return may not
materialize. Instability may also be lacking in the absence of
better deep moisture.

The current forecast assumes moisture return will be somewhat
limited with a fast system whose timing falls between the GFS and
ECMWF solutions. Kept PoPs across the eastern half of the area
Friday into Saturday, although this will need further refinement as
models continue trending toward one another. Temperatures will
gradually climb through the week as higher thickness air is
entrained north. Once the front crosses, high pressure and much
drier air build in with temperatures falling some, although the
best of the colder air will remain to our north and east.

Used an equally weighted model blend through Friday, then began
nudging more to the ECMWF, mainly to reflect timing uncertainty with
the late week system.
&&

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

$$



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