Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Little Rock Arkansas
534 PM CST sun Dec 4 2016
Updated to include the 00z aviation discussion below...
Lows ceilings will continue through much of the period...with some
occasional improvements possible before the rainfall moves in.
However...overnight...some patchy fog will be seen...though only
some patchy dense fog is expected at this time. Rain chances will
increase from the south during the daytime hrs on Mon...with
rainfall spreading from south to north throughout the day. Do not
expect any major improvements in flight conditions through the
period...especially once the rainfall develops.
Previous discussion...(issued 241 PM CST sun Dec 4 2016)
Short term...tonight through Tuesday...
Upper low remains over northwest Mexico and is gradually making its way
toward our area. Models continue to bring the trof into the area
Monday night into Tuesday morning. ECMWF, Canadian, and GFS have the
low passing south of the state, or along the southern border, while
the NAM and navgem prefer to bring it more into central Arkansas.
Regardless, rain chances should start increasing steeply tomorrow
morning, and I have high pops across the entire area tomorrow
afternoon and evening.
Steepening midlevel lapse rates associated with the low and
increasing upper level divergence should help to support some
embedded thunderstorms. With the potential for the low to track a
bit further north than the European model (ecmwf)/GFS/Canadian consensus, I have
opted to put thunderstorm chances a bit further north than spc's
guidance, although I did keep the mention out of the northernmost
Rain chances tonight should remain mainly across the southern half
of the state. I am concerned about the development of fog overnight,
mainly across the northern half of the state as the lower cloud
cover starts to clear out. I have the mention of patchy fog
overnight or toward morning in all of the areas, and went with the
mention of more widespread fog in the more favored valley areas of
northern and western Arkansas.
Long term...Tuesday night through Sunday...
Overcast and dreary conditions continue Tuesday night although no
measurable precip is expected ahead of the next weaker system and
Arctic front that will be approaching the area from the northwest.
The weak shortwave and associated surface low will provide enough
lift and moisture to squeeze out some light precip across the area
Wed and and Wed night. Most of the precip will fall as light rain
showers Wed, but things get a more tricky Wed night. As temps fall
rapidly behind the front...some of the rain could briefly mix with
or change to light snow before the precip comes to an end well
before sunrise Thu, mainly across northern AR, and especially in
the higher elevations. Still, little or no accumulations or
impacts are expected at this time.
All precip is expected to end by sunrise and be replaced with
sunshine and cold conditions as Arctic high pressure dominates the
weather picture Wed through Fri. Very gradual warming is now
expected over the weekend although some very light precip could
break out Sat night through Monday due to the moist return flow from
the Gulf and a very weak mid level shortwave approaching in the
zonal flow. The early concern of another Arctic front on Sunday no
longer appears likely.
Cold temps will be a concern Wed night through Friday night with
much below normal temps expected. Thu will be particularly nippy
with highs in the 30s and lower 40s, along brisk north winds will
keep wind chill temps in the 20s. By far the coldest air of the
season expected Thu night with temps falling into the teens and
lower 20s. Only slightly warmer Sat and sun with temps topping out
mainly in the 40s both days.