Area Forecast Discussion
Issued by NWS Little Rock, AR

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FXUS64 KLZK 251120 AAA
AFDLZK

Area Forecast Discussion...UPDATED
National Weather Service Little Rock AR
620 AM CDT Mon Sep 25 2017

.AVIATION...
LIFR ceiling at Hot Springs and MVFR visibility there and
Arkadelphia will improve fairly quickly after sunrise as winds
pick up. Otherwise, VFR conditions will be prevalent through much
of the next 24 hours. Isolated storms will be possible this
afternoon, but at this time, confidence isn`t high enough to
include in most terminals right now.
&&

.PREV DISCUSSION...(ISSUED 409 AM CDT Mon Sep 25 2017)
SHORT TERM...Today Through Tuesday Night
I`ve pretty much run out of creative ways to say little or no
change to the going forecast without sounding like a broken
record. Apparently the current weather pattern has also run out of
ways to express itself. I mean, 65-plus dewpoints all day, and
90-degree temperatures in the afternoon? Come on, it`s late
September! But, I digress.

Anyway, since it is part of my job to try to explain things, I
guess I will press on anyway.

Analysis this morning shows surface high pressure to the
northeast of Arkansas, with a stalled frontal boundary out in the
plains generating convection. While this stuff won`t be a concern
for us, upstairs, we`ve got a 500 millibar elongating closed low
centered near the Arklamiss region. While we won`t have the
surface-based forcing for large-scale or widespread convection,
presence of the low will be enough to provide support to any
convection that generates as daytime heating interacts with any
mesoscale boundaries over the region this afternoon. Yesterday,
high temperatures were in the 90s in much of the area. I see no
reason this won`t be the case today.

Aforementioned upper low will dampen out and get absorbed in the
mean flow into Tuesday. Ridging that has kept the front in the
plains at bay for a few days will finally relax some, and this
will allow the front to move into the region Tuesday night.
However, with minimal low-level moisture return ahead of the
boundary, only post-frontal precipitation is expected, and this
will be widely scattered at best.

As has been the case the last few mornings, fog has formed in
places. However, visibility restrictions aren`t expected to be
widespread, and the fog will scatter out as the gradient picks up
around or a little after sunrise.

LONG TERM...Wednesday Through Sunday
To begin the period, synoptic progs show split flow pattern with a
progressive northern stream across the northern CONUS and a cutoff
low over the Desert Southwest. Hurricane Maria will be gliding north
off the East Coast while upper ridging remains a fixture closer to
home. While there is tolerable agreement among models for the first
half of the period, the GFS continues painting higher precipitation
across the area Wed and Thurs, with the ECMWF less enthusiastic
about precip across most of AR. Given the placement of the upper
ridge and persistent northerly flow locally, thinking the best
moisture will remain just to our west, across the Southern and
Central Plains. Did blend ECMWF guidance in more heavily than GFS
guidance and tried to weight that with a more general model blend to
generate PoP grids through Thurs. This solution keeps high-end
slight chance to low-end chance PoPs across northwestern AR.
Uncertainty exists in the northward extent of more stout upper
ridging and the evolution of associated deep moisture fields, and
latest guidance keeps us near the transition zone between stagnant
flow to the south and the more progressive flow to the north, so
lower-than-average confidence as of this morning.

Through the latter half of the period, the Southwestern cutoff low
will begin to eject northeast and phase with the northern stream as
a large upper trough digs into the Great Lakes region. Majority of
models show large scale amplification of the longwave pattern as a
result, but consensus rapidly decreases among operational guidance
thereafter with the GFS attempting to generate a gigantic blocking
ridge from Canada to the Gulf. Ensemble members also highlight
rapidly decreasing confidence through the weekend. In any case, with
the moisture plume remaining west of us and continued northerly
surface flow under the upper ridge, the weather should remain quiet
and mild with increasing fire danger as winds could occasionally
gust, especially through the MS River Delta. Stuck close to guidance
for temps, although did tweak down just a hair...perhaps
optimistically...given the chance of lowering thicknesses
periodically intruding from the north.

FIRE WEATHER...
Much drier air will start filtering in late Tuesday behind a cold
front, with precipitation chances remaining low owing to a lack
of deep moisture. Monthly rainfall to date remains below 50
percent of normal for many areas, with D0 drought conditions
observed through large portions of the state. Continued drying of
fuels is expected and a building upper ridge will allow this trend
to continue. North to northeasterly surface winds will increase
behind the front, particularly in the afternoons, with some gusts
approaching 15 mph across the MS River Delta. Fire danger will
continue increasing through the forecast period with minimum RH
percentages dropping into the lower to mid 30s beginning Thursday.

&&

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

$$


Aviation...57



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