Area Forecast Discussion
Issued by NWS Little Rock, AR

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FXUS64 KLZK 010429 AAA
AFDLZK

Area Forecast Discussion...UPDATED
National Weather Service Little Rock AR
1029 PM CST Wed Nov 30 2016

.AVIATION...
VFR conditions will prevail through the period, with no
significant weather or obstructions to visibility. Winds will be
westerly around 6 knots or less, becoming light and variable after
sunset on Thursday. Tafs will be sent at 0520Z.
&&

.PREV DISCUSSION...(ISSUED 506 PM CST Wed Nov 30 2016)

AVIATION...
Gradient will continue to relax over the next hour or so, with
winds becoming westerly around 6 knots or less. VFR conditions are
expected through the period, with no significant weather or
obstructions to visibility. Tafs out shortly.

PREV DISCUSSION...(ISSUED 308 PM CST Wed Nov 30 2016)

DISCUSSION...
Main concerns in this forecast cycle are temperatures through
Friday with dry weather, then rain for the weekend and into early
next week. At this time, threat of any severe storms over the
weekend and into next week appear very low.

Clouds have gradually thinned from west to east today as the
upper low pressure trough moves through the region. Most areas
currently are mostly sunny, with an elevated west to northwest
wind at 10 to 25 mph. The cooler and drier air has help breakup
the clouds, and afternoon temperatures were from the mid and upper
40s to lower 50s over the north, while 50s central to south.

SHORT TERM...Tonight Through Friday Night
As the surface and upper high pressure systems settle over the
region, mainly clear nights and mostly sunny days will be seen.
Lows with be from the 30s tonight, to the 30s and some 40s Friday
morning, to the 30s with mainly 40s Saturday morning. Highs will
be from the 50s to lower 60s. Clouds will gradually increase from
the west later Friday and into Saturday, as the chance of rain
increases with energy seen in the upper southwest flow into AR. At
this time, the threat of severe storms appears to very low.

LONG TERM...Saturday Through Wednesday
Assuming that a relatively cool and dry air mass is in place over
the region on Friday...a strong upper level trough moving towards
the South Plains will set the stage for our next chance of rain
across Arkansas on Saturday. As this large upper trough approaches
the Southern Plains...a broad warm air advection regime is expected
to set up over much of Texas...extending east over Arkansas and
Louisiana. A cool and dry low-level airmass is key here because the
warm air advection regime is expected to transport an airmass
characterized by high theta-e values back up over AR/LA on Saturday.

A cool and dry low-level air mass represents an air mass
characterized by a low theta-e value. With all models showing a high
theta-e airmass advecting north over the region on Saturday out
ahead of this upper trough...a cooler and drier low-level airmass
will only accentuate the lift associated with high theta-e air
returning over the region. This strong warm air advection aloft will
result in strong moist isentropic ascent over Arkansas representing
a good chance for widespread rain showers across the state. By
Saturday evening most models show a strong low-level jet developing
over southeast Texas and all of Louisiana. This low-level jet core
also represents an area of strong forcing for ascent near the
Arklatex borders. Strong isentropic ascent combined with the
acceleration of warm air advection on the nose of this low-level jet
should set up a band of moderate to heavy rainfall from late
Saturday afternoon through the overnight hours. At this time it
looks as though the axis of heaviest rainfall will remain south over
northern Louisiana...but we will keep a close eye on this axis in
later forecasts.

Outside of widespread cold rain and a small chance for heavy
rainfall across southern Arkansas...high impact weather appears
unlikely with Saturday and Saturday night`s rainfall at this time.
There is some concern for a mix of cold rain and wet snow across
northern Arkansas Saturday morning...however kept the forecast as
all rain at this time. The NAM advertises the onset of rainfall with
850 mb temperatures of minus 1 deg C. The GFS and ECMWF both keep
850 mb temperatures above freezing...so confidence in any snow
mixing in with rain is very low at this time. Regardless... even in
the NAM the surface dew point remains above 2 deg C...so no icing or
accumulation would be expected even if the NAM solution verifies.
Anytime winter weather is a concern the forecast is definitely worth
monitoring closely...however the chances of snow mixing in with rain
across northern Arkansas look low at this time.

Sunday and Sunday night...Expect to see a slight break in the
rainfall during this time as the warm air advection regime weakens
as the large upper trough off to the west breaks into a northern and
southern half. The northern half of the trough is expected to move
quickly east Saturday night resulting in some weak shortwave ridging
over Arkansas on Sunday. The lull in the warm air advection regime
and shortwave ridging will keep rain chances somewhat low from
Sunday to Sunday night. Some very light rain may persist in the weak
warm air advection regime that lingers...but widespread rainfall
should come to an end by late Sunday morning.

Monday...Widespread rain showers are expected to spread across
Arkansas once again on Monday as the southern half of the upper
trough lifts northeast over the state. If the trough lifts directly
over Arkansas... strong large scale forcing for ascent in the form
of differential positive vorticity advection should result in
numerous rain showers across the state on Monday. Thunderstorm
activity looks unlikely at this time...but may be possible if warm
air advection is stronger than currently advertised in guidance.

Tuesday and Wednesday...Rain showers are expected to dissipate
across the state late Monday night as large scale forcing for
subsidence works its way over the region behind the upper trough.
Tuesday is expected to remain dry...but at least a small chance of
rain returns to the forecast on Wednesday as another strong upper
trough makes its way over the Southern Plains and towards Arkansas.
This far out confidence in the strength and timing of this mid-week
system for next week is very low...however the upper trough looks
quite strong 7 days out...so it will be interesting to see if it
maintains this strength in later forecasts.
&&

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

$$

Aviation...57


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