Area Forecast Discussion
Issued by NWS Little Rock, AR

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281
FXUS64 KLZK 170130
AFDLZK

Area Forecast Discussion
National Weather Service Little Rock AR
730 PM CST Mon Jan 16 2017

.AVIATION...17/00Z TAF CYCLE

CDFNT was located acrs WRN AR early this evening. An area of SHRA/
WDLY SCTD TSRA wl cont sloly EWD thru Central/Southeast AR thru
tngt. The frontal bndry wl eventually work thru the FA tngt and
early Tue, eventually stalling E of the area. Combo of VFR/MVFR
conds are expected acrs along and ahead of the bndry tngt, with
lower conds where heavier rain occurs. Low clouds wl move back
into NRN AR later this evening, producing MVFR CIGS thru much of
the PD. Patchy fog wl also be noted in some areas overnight. /44/
&&

.PREV DISCUSSION...(ISSUED 254 PM CST Mon Jan 16 2017)

SHORT TERM...Tonight Through Wednesday
20z subjective surface analysis indicates a warm front from near
Harrison, to Batesville. A cold frontal boundary was noted across
eastern Oklahoma. Dew points have reached the upper 60s across
extreme southwest sections of the forecast area.

Near term forecast soundings suggest there will be a short window
of opportunity for convection to obtain low level organization
late this afternoon, in an area generally along and south of a
line from Arkadelphia, to Pine Bluff. This window will quickly
close with the loss of solar heating.

The cold front will align itself across southern sections of
the forecast area early Tuesday, before moving north as a warm
front on Wednesday. Precipitation forecasts will reflect patterns
of expected isentropic lift associated with energy approaching in
southwest flow.

LONG TERM...Wednesday Night Through Monday
At the start of the extended forecast period...a large upper trough
is expected to be located over the Central and Southern
Plains...moving slowly to the northeast towards Arkansas. Broad
large scale forcing for ascent will be in place over Arkansas
because of the large upstream upper trough. What is uncertain is
where synoptic scale surface features will set up across the state
from Wednesday night through Thursday.

The ECMWF advertises an inverted surface trough oriented
approximately along the Mississippi River. If this verifies...much
of northwest Arkansas will remain rain free as the position of the
surface trough would lead to north or northeasterly winds over
northwestern Arkansas which represents cool and dry air advection.
Rain chances would be concentrated over the eastern portion of the
state with central Arkansas holding on to a chance for scattered
rain showers.

The GFS brings this surface trough across central Arkansas which
favors a stronger low-level warm air advection regime over much of
the state Wednesday night through Thursday morning. If this model
solution verifies then all of Arkansas would have a good chance at
seeing some rain during this period...and the chance of
thunderstorms would also be greater with warm and humid air creeping
farther northwest across the state.

Regardless of which solution verifies...showers and thunderstorms
are expected to move east away from Arkansas Thursday night as
strong forcing for subsidence builds over the state as the upper
trough lifts off to the northeast. Rainfall totals are expected to
range between 1 to 2 inches to the east of the inverted surface
trough...so definitely favoring eastern Arkansas over other portions
of the state for where the heaviest rain will fall by the end of the
week.

This weekend...A second powerful upper trough is expected to move
east-northeast out of the southwestern CONUS and towards Arkansas
for Sunday. Because of the strong subsidence from the departing
trough on Friday...think that rain chances on Saturday will remain
quite low as it will take quite a bit of lift to remove the
subsidence inversion from the state...and to moisten up the
troposphere once again. All of Saturday`s lift will likely be spent
undoing Friday`s subsidence...so the balance is expected to be a
return of cloudy skies...but very low rain chances. As the strong
upper trough gets closer to Arkansas...the lift will intensify and
rainfall will become much more likely across the state Saturday
night into Sunday as a result. Think that the chances for widespread
thunderstorm activity are somewhat low because of the short turn
around time in between upper troughs. However if the upper low moves
directly over the state on Sunday as the ECMWF/GFS advertise...then
the cold air aloft could destabilize us enough to allow for some low-
topped thunderstorm activity Sunday afternoon. It`s too early to
determine if this cold core upper low passing over the state will
destabilize us enough for severe thunderstorm activity... but will
watch its evolution closely as we get closer to the upcoming
weekend.

Early Next week...Monday and Tuesday will likely be dry...depending
on the speed of the departing upper low. Temperatures will be cooler
behind the upper low...but not exactly cold as the polar jet stream
remains north of the state. Models indicate that another strong
upper low will move over the state bringing another chance of rain
to Arkansas by the middle of next week

&&

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

$$


Aviation...99



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