Flash Flooding and Flooding in Arkansas, December 22 to 23, 2017

Area Forecast Discussion
National Weather Service Little Rock AR
632 AM CST Fri Dec 22 2017

.AVIATION...22/12Z TAF CYCLE

Rain wl become widespread acrs the FA as today progresses, as a
frontal boundary stalls out over central AR. Pilots can expected
IFR conds to prevail, with some MVFR conds at times over SERN AR
ahead of the front. The front wl eventually work to the SE late
today and tngt, with Sctd TSRA expected ahead of it. /44/
&&

.PREV DISCUSSION...(ISSUED 440 AM CST Fri Dec 22 2017)
SHORT TERM...Today Through Saturday Night

Contending with several features over the AR this mrng. A CDFNT was
situated ovr NW part of the state. Meanwhile, a warm front extended
roughly along the AR River valley from a sfc low ovr the Wrn part of
state. Seeing about a 20 degree temp spread ovr the FA this mrng,
with mid 40s in the NW and mid 60s in the S. Have seen Sctd showers/
few storm form ovr the area the last few hours as WAA/lift commences.

In a nutshell, rain wl cont to increase in coverage and persist acrs
AR today and much of tngt. The aforementioned CDFNT wl eventually
bcm quasi-stationary over the central part of the state later today
as it aligns itself with the SW steering flow aloft. The bndry wl
provide a focus for locally heavy rains as a series of upper lvl
impulses affect the region. A FF watch is already posted thru tngt
for locations along and south of the I-30/40 corridor.

Meanwhile, the primary upr lvl storm system will track to the east
out of the 4-corners region over the next 24 hours, eventually
passing acrs AR. This wl eventually push the CDFNT out of the area
heading into Sat. Some organized convection wl be possible ahead of
the CDFNT later today and early tngt, primarily ovr the SE half of
the FA. A few strong/severe storms wl be possible, with damaging
winds and large hail the main concerns.

Rain wl gradually taper off from the W late tngt/Sat morning as the
main upr trof swings to the E of the region. Cannot rule out some
snow mixing with the rain ovr part of NW AR early on Sat, especially
in the higher terrain, as colder air advects in. Still appears that
the bulk of the sig moisture wl be E of the area at that time, with
little in the way of snow accumulation expected. Although some of
the higher elevations could see a light dusting of snow, travel
problems are not anticipated. Drier and colder conds wl prevail to
round out the period.

LONG TERM...Sunday Through Thursday

A large scale trough will be centered over the central plains around
daybreak Sunday, but will quickly shift east through the day. From
midnight Sunday night through basically the middle of next week, the
upper pattern will, in general, feature broad and cyclonic flow
across the northern half of the United States. The focus for the
long term will really be for the Tue night through Thursday time
frame as Sunday through Tuesday will be dry and fairly non-eventful.

Speaking of Sunday, previous forecasts and model output showed the
potential for some light snow across northern Arkansas. However, the
latest data no longer supports this. Temperature profiles will be
cold enough, but the lack of moisture means little if any precip
will be realized. So I have removed any mention of wintry precip on
Sunday as a result.

The next period of concern is the Tuesday night through Thursday
time frame. There are stark and significant differences between the
GFS and ECMWF in how they handle the possibility of widespread
rainfall and perhaps some wintry precipitation. The ECMWF is notably
drier, showing only some light precipitation amounts over southern
Arkansas Tue night into Wed morning, with a dry forecast from midday
Wed through the end of the period. The reason it's drier is that
surface high pressure to the north of Arkansas has more favorable
flow into the state, thus pushing the front and associated
precipitation out of the state more effectively. It's also notably
cooler. The GFS on the other hand, is warmer in general but also has
more widespread rainfall across the state. Attempted to compromise
between the two extremes, with 20-30 percent chances for
precipitation across much of the forecast area for Tuesday night
through the end of the period. But this is a very low confidence
forecast. Time will tell whether precip chances need to be adjusted
in time or areal coverage, and also whether any wintry precipitation
is actually a genuine threat.
&&

.LZK Watches/Warnings/Advisories...
Flash Flood Watch through Saturday morning FOR Arkansas-Bradley-
Calhoun-Clark-Cleveland-Conway-Dallas-Desha-Drew-Faulkner-
Garland-Grant-Hot Spring-Jackson-Jefferson-Lincoln-Lonoke-Monroe-
Montgomery-Ouachita-Perry-Pike-Polk-Prairie-Pulaski-Saline-White-
Woodruff.
&&

Hazardous Weather Outlook...UPDATED
National Weather Service Little Rock AR
737 AM CST Fri Dec 22 2017

ARZ003>007-012>016-021>025-030>034-037>047-052>057-062>069-230500-
Boone-Marion-Baxter-Fulton-Sharp-Newton-Searcy-Stone-Izard-
Independence-Johnson-Pope-Van Buren-Cleburne-Jackson-Logan-Conway-
Faulkner-White-Woodruff-Scott-Yell-Perry-Polk-Montgomery-Garland-
Saline-Pulaski-Lonoke-Prairie-Monroe-Pike-Clark-Hot Spring-Grant-
Jefferson-Arkansas-Dallas-Cleveland-Lincoln-Desha-Ouachita-
Calhoun-Bradley-Drew-
737 AM CST Fri Dec 22 2017

This Hazardous Weather Outlook is for a Large Part of Arkansas.

.DAY ONE...Today and Tonight

Some patchy fog, dense at times, will be seen across parts of the
state through the morning hours. Otherwise, heavy rain will
affect the southeastern half of the state today and tonight.
Rainfall amounts of 2 to 4 inches, with locally heavier amounts,
can be expected east of I-30 and along and south of the I-40
corridor east of Little Rock during this time period. Flash
flooding will be a possibility as well, especially later today as
rainfall amounts begin to add up. Widespread severe weather is not
expected, but a few strong storms may develop later in the day
across southeast Arkansas.

Additionally, late tonight and early Saturday morning, rainfall
may change over to a mix of rain and snow in far northern and
northwestern Arkansas. No significant impacts are expected, but
minor accumulations of snow may be possible.

.DAYS TWO THROUGH SEVEN...Saturday Through Thursday

Light snow will be possible in far northern Arkansas around and
shortly after daybreak Saturday as precipitation comes to an end.
Only minor accumulations will be possible.

Tuesday through Thursday next week may see another round of
widespread precipitation across Arkansas, though amounts are not
expected to be heavy. At this time, it is unclear whether there
will be a threat of wintry precipitation or not.

.Spotter Information Statement...

Spotter activation will not be needed.

&&

Visit NWS Little Rock on the web. Go to http://weather.gov/lzk.

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