Area Forecast Discussion
Issued by NWS Little Rock, AR

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FXUS64 KLZK 161227

Area Forecast Discussion
National Weather Service Little Rock AR
627 AM CST Wed Jan 16 2019


Clouds wl cont to sloly incrs acrs the FA this mrng. Most
locations can expect low end VFR CIGS thru much of today, with
some MVFR conds at times. Expect CIGS to lower tngt, with
widespread MVFR/IFR conds by Thu mrng. Areas of light drizzle and
fog wl form overnight acrs the FA. /44/

.PREV DISCUSSION...(ISSUED 430 AM CST Wed Jan 16 2019)
SHORT TERM...Today Through Thursday Night

Early this mrng, sfc high pres was situated to the SE of AR, with
light S/SW winds noted over the FA. After a mostly clear start to
the night, low clouds were sloly increasing over the area. Where
skies have stayed clear, patchy freezing fog was noted.

Moisture/clouds wl cont to overspread the FA today in advance of a
new storm system taking shape over the intermountain west. The upper
lvl trof wl work into the Srn Plains later today, allowing for an
assocd sfc low to form. The sfc low wl quickly move to the E,
eventually passing N of AR later tngt and early Thu.

Sctd showers wl form tngt and cont into Thu out ahead of fnt. Bulk
of the rain chances wl shift E of the area Thu aftn, as pre-fntl
trof passes thru, and drier low lvl air works in on SW winds. The
actual CDFNT wl pass acrs AR Thu evening, followed by a brief shot
of drier and cooler air.

LONG TERM...Friday through Tuesday

For the most part, there are no significant changes to the forecast
this cycle with widespread rain, some wintry weather, and bitterly
cold Arctic air anticipated over the weekend. Model agreement
remains high through early next week, so nudged the previous
forecast based on the 00Z suite of guidance. Slight preference was
given to the ECMWF given its better run-to-run consistency compared
to the GFS. Interestingly, the GFS did yield a much warmer solution
with the weekend system -- in some instances, temps with the 00Z run
were 5 to 10 degrees warmer than the 12Z solution. Did increase
weekend temps a touch but continuing to highlight bitter cold Sunday
and Monday morning where lows will be in the 10s to 20s across a
majority of the state. A synopsis of the pattern and pertinent, gory
details are below.

A large upper trough will dive through the southwestern CONUS
Friday, spurring deep and rapid surface cyclogenesis in the lee of
the Rockies. Attm, the surface cyclone is progged to track across
the Red River Valley overnight Friday, arriving in western AR by
Saturday morning. Model guidance exhibits general agreement with
this evolution and continues highlighting a significant pressure
gradient associated with the surface feature. An attendant cold
front extending south from the cyclone will sweep east as well and
traverse the MS River Valley later Saturday. In its wake, an Arctic
surface high will slide in from the north, bringing with it the
coldest temps so far this season and potentially dangerous cold.
Snow remains possible with minor accumulation in the north and west.

As multi-scale forcing for ascent increases ahead of this system
Friday afternoon, expecting rain to overspread the area from the
west. Marginal instability on the order of a few hundred J/kg MLCAPE
may support isolated thunder, primarily across the southeastern two-
thirds of the state, although no severe weather is expected. The
front will sweep through during the day Saturday with temps
following a definitively non-diurnal trend. Very strong CAA is
anticipated in the wake of the front and forecast soundings indicate
substantial cooling within the column as the depth of the cold air
mass increases. Did include some mixed wintry precip on the leading
edge of the Arctic air mass Saturday afternoon where subtle warm
nosing may exist, but thinking a change to all snow will be fairly
quick given the magnitude of CAA. Accumulating snow will be possible
generally between Saturday afternoon and early Sunday morning across
northern AR. Some minor accumulations are also possible in the
higher terrain of the Ouachitas in western AR. Elsewhere, while a
change to snow will be possible, accumulations are not anticipated
as moisture quickly exits to the east by dawn Sunday morning.

The impressive pressure gradient anticipated with this system
indicates strong winds will be possible if not likely, especially in
higher terrain and across the MS River Delta. Raw model output
appeared to be unduly conservative with its handling of winds, so
increased the numbers quite a bit, particularly considering our
ability to overachieve with winds/gusts during events like these.
Northerly winds sustained in the 20 to 30 kt range with gusts to 40
plus kts are not at all unrealistic, so relatively confident with
the higher wind solution this forecast cycle. Expect winds to begin
increasing late Friday with the highest speeds late Saturday through
Sunday morning. The combination of wind speeds and temperatures,
particularly Sunday morning, will drive apparent temps to near or
slightly below zero in the north with low 10s elsewhere.

By Monday, the Arctic surface high begins sliding east and its
influence will wane as heights begin building aloft. Temperatures
will moderate in response with highs returning to the 40s and 50s
and lows climbing back into the 20s to near 40 degrees. Additional
upper troughing is likely heading towards the mid-week time frame,
although significant model discrepancies are apparent attm. Did
include scattered rain with some potential for snow in the north
late Tuesday.

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

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