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Area forecast discussion...updated 
National Weather Service Little Rock Arkansas
503 PM CST Fri Dec 2 2016

Discussion...

Updated to include the 00z aviation discussion below...

&&

Aviation...

VFR conditions are ongoing at this time...but this will change
late tonight and especially on Sat as moisture lifts north.
Rainfall will develop and lift north into the state overnight.
Initially...VFR conditions are expected as very dry air remains
near the surface. However...as the rainfall intensity increases...do
expect visible/cigs to drop during the day from south to north on Sat.
The decreased flight rules will continue off an on through the end
of the taf period.

&&

Previous discussion...(issued 302 PM CST Fri Dec 2 2016)

Discussion...

Main concerns in this forecast cycle are chances of rain starting
late Friday night, over the weekend, and even into next week.
Severe storm threat appears to be quite low with more of a
stratiform rain event. Finally the temperature forecast will be
challenging due to cold air advection, clouds and rain over the
state.

Surface high pressure has moved more east, and a southeast to
south surface wind flow has returned to Arkansas. While the atmosphere
has remained dry today with dew point temperatures in the 30s to
upper 20s. This dry air will hold back the rain a bit more on
Saturday and the rest of the weekend. The upper pattern has the
high pressure ridge over the Southern Plains, while up stream in
the southwest flow, shortwave energy is seen with increasing
clouds over TX and the Southern Plains.

Short term...tonight through Sunday night

Tonight will see increasing clouds over AR, with the chance of
rain gradually entering the southwest and west. Due to the dry
in-place atmosphere, it may take sometime to saturate the airmass
and rain reach the ground. Once it does, plenty of rain is
forecast for the weekend. This event will mainly be a rain and
shower event, with little thunder seen and mainly over southern
Arkansas. Rain amounts through Sunday night will be the highest over
southwestern and southern AR, with 1 to 2 inches with isolated
higher amounts, while over central around 1 inch with isolated
higher amounts, and northern Arkansas with generally less than an inch.
Flooding or flash flooding will generally be a low threat,
however we are in the none growing season now, and much of the
rain will drain slower and keep the ground quite wet. Otherwise,
the rain will gradually lessen and end Sunday night as the system
moves east and out of Arkansas. Temperatures will be chilly and only
reach the 40s to lower 50s this weekend. Normal highs would be in
the 50s. Damp and chilly weather will rule the weekend.

Long term...Monday through Friday

Monday...a cut off low over northern Mexico is expected to lift
northeast towards Arkansas on Monday as a strong but compact
shortwave trough. There are some differences in model guidance
regarding the dynamic evolution of this trough as it moves northeast
towards the state Monday evening. Models had been showing the trough
becoming negatively tilted as it moves over Arkansas...which the NAM
still supports. However the latest 12z runs of the GFS and European model (ecmwf)
maintain more of a neutral if not slightly positive tilt to the
trough through Monday evening.

The tilt of the trough will simply impact the intensity of rainfall
over Arkansas from Monday and Monday night. Farther to the
southeast, it will play a role in chances for severe storms...
however regardless of the model solution...confidence is very high
that the severe storm threat area will remain well southeast of
Arkansas Monday and Monday night. A negatively tilted trough would
allow mid-level lapse rates to steepen and increase the chance for
isolated to scattered thunderstorms within the broad area of rain
showers expected to develop over the state out ahead of the trough.
The current forecast calls for a solid half inch of rain across the
state Monday through Monday night. If the approaching trough becomes
negatively tilted as it approaches Arkansas...embedded convection
could double that rainfall total wherever thunderstorms are more
prevalent than rain shower activity.

Tuesday through Thursday...precipitation is expected to come to an
end quickly Tuesday morning as strong forcing for subsidence works
its way across Arkansas behind the upper trough. Behind this upper
trough the remainder of the forecast will be determined by the
evolution of a second...but much larger and stronger upper trough
moving towards the Great Plains from the northwest. The GFS has this
large trough moving over the north central Continental U.S. On Wednesday
sending a cold and dry airmass south across Arkansas and keeping
precipitation chances very low for the remainder of the forecast.
The European model (ecmwf) continues to advertise this large upper trough moving over
the north central Continental U.S. In two distinct pieces.

In this solution the second significant piece of upper level energy
moves over the Central Plains and towards Arkansas on Wednesday
sending a strong cold front through Arkansas bringing another good
chance of rain across the state along and just behind this front.
The GFS had been on board with the European model (ecmwf) solution until yesterday...
however over the past 24 hours the models have maintained their
disagreement. At this time kept some low rain chances in the
forecast for Wednesday anticipating the passage of a strong cold
front across the state. If there is any significant moisture in
place out ahead of this front...would expect scattered to numerous
showers to accompany the front across the state.

Regardless of which model solution verifies...an Arctic airmass is
expected to build across Arkansas Wednesday night into Thursday. Low
temperatures on Thursday morning are expected to range from the
upper teens across the northern part of the state to the low 30s in
the southeast. If there is any lingering precipitation behind the
front Wednesday evening...there is a chance that rain could change
over to snow before coming to an end Wednesday night. At this time
have a mention of rain or snow in the forecast for the higher
terrain of the Ozark and Ouachita Mountains...and generally across
northern Arkansas.

Think that the most likely scenario is that if there is any
precipitation at all associated with the frontal passage on
Wednesday...that precipitation will come to an end before it gets
cold enough to change over to snow. Looking at raw model fields it
is often misleading looking at 6 hour precipitation totals and
surface temperatures at the same time. Looking at model guidance
online the precipitation total field (qpf) is typically a 6 to 12
hour aggregate field while the temperature at the end of the valid
time period (here midnight Wednesday night/Thursday morning) is an
instantaneous field. It can be misleading if a user simply looks at
both fields for the same valid time. At any rate...the threat for
accumulating snow looks very low at this time. We will watch this
system closely though as there is at least a small chance to see
some light snow Wednesday night across northwest and northern
Arkansas.

&&

Lzk watches/warnings/advisories...none.
&&

$$

Aviation...62

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