Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 160502
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1102 PM CST Sun Jan 15 2017

.UPDATE...
Issued at 924 PM CST Sun Jan 15 2017

Most of the light rain has shifted northeast of our forecast area
this evening. There is still fog across much of the area along with
patchy drizzle. The HRRR and latest NAM model runs bring another
round of rain northeastward into central and northeast MO and
west central IL late tonight/early Monday morning well ahead of an
approaching upper level low and associated surface low moving into
the central Plains and north of a warm front. Temperatures in
northeast MO and west central IL were still near the freezing
mark this evening, but these should be slowly rising overnight.

GKS

&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 326 PM CST Sun Jan 15 2017

Freezing line continuing to lift northward through region this
afternoon. So freezing rain slowly changing over to all rain from
south to north. Have expired/cancelled Ice Storm Warning and
replaced portions over northeast MO, west central IL with a Freezing
Rain Advisory til 6 pm. Any ice accumulation in this area will be
less than a tenth of an inch.

Otherwise, most locations to see a bit of a break from precipitation
til after 06z tonight. Main shortwave/trof over southwestern US to
lift northeastward towards area with increasing surface temps and
low level moisture. So precipitation chances to be on the increase
after 06z Monday. During the day on Monday, surface dewpts to rise
into the low 40s to low 50s, decent low level jet and MU capes
between 100 and 500 J/kg, so slight chance of thunderstorms, mainly
during the afternoon hours.

As for temperatures, with system lifting northeast towards region,
will see steady or increasing temperatures tonight. Decent WAA ahead
of system on Monday with highs in the low 40s to upper 50s, a good
10 to 15 degrees above normal for this time of year.

Byrd

.LONG TERM...  (Monday Night through Next Sunday)
Issued at 326 PM CST Sun Jan 15 2017

The models are in relatively good agreement with the large scale
features Monday night into early Tuesday with the upper low moving
from NW MO into the lower Great Lakes. The associated surface low
will follow a similar track with the southward trailing cold front
sweeping across the entire area Monday night, and located east of
the CWA by 12z Tuesday. Good deep large scale ascent will continue
to favor showers/rain through the warm sector ahead of the front
on Monday night, with weak instability supporting isolated
thunderstorms. Tuesday will be largely dominated by weak CAA in
the wake of the cold front and extensive post-frontal stratus.
Temperatures while cooler than Monday, will still be above
average. There is a secondary northern stream short wave trof
progged to dig from the northern Plains into the mid/upper MS
Valley in the Monday night-Tuesday Night time frame. The GFS is
the odd model out with a slower solution showing more digging, and
this could maintain clouds longer and even help generate some
spotty pcpn if correct. At this time it has been largely discounted.

By Wednesday, a low level WAA regime gets well underway and this
should promote well above average temps at least on Wednesday. The
models diverge during the later part of the week with the
evolution and northeast movement of the lagging southwestern U.S.
upper low/trof. Both the GFS and ECMWF are similar bringing this
lifting upper trof/low into the MS Valley in a negatively-tilted
fashion however differ by timing on the order of 18 hours, with
the ECWMF faster centered from late Wednesday night-Thursday
night. Regardless of timing, temps should be above average, its
just how much above average and then timing on the attendant
threat of showers and maybe thunder. In the wake of this system,
deep southwesterly flow will evolve into the weekend keeping above
average temps going strong.

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1044 PM CST Sun Jan 15 2017

Very low stratus cloud deck, below 500 feet along with fog,
likely becoming dense in COU and the St Louis metro area late
tonight, will continue through at least Monday morning. Rain will
spread eastward into COU late tonight and into the rest of the taf
sites early to mid morning ahead of an approaching low pressure
system and north of a warm front. There may be some embedded
thunderstorms, but will leave TSRA out of the tafs for now.
Easterly surface wind will veer around to a southeast direction on
Monday and strengthen as the surface ridge centered over the Ohio
Valley region shifts eastward.

SPECIFICS FOR KSTL: Very low stratus cloud deck, below 500 feet
along with dense fog will continue through at least Monday
morning. Rain will spread eastward into the STL area by mid to
late morning ahead of an approaching low pressure system and north
of a warm front. There may be some embedded thunderstorms, but
will leave TSRA out of the STL taf for now. Easterly surface wind
will veer around to a southeast direction on Monday and strengthen
as the surface ridge centered over the Ohio Valley region shifts
eastward. The surface wind will veer around to a westerly
direction late Monday night after the pasage of a cold front. The
rain will also move out of STL by late Monday night.

GKS

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Dense Fog Advisory until 10 AM CST Monday for Boone MO-Callaway
     MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-Iron MO-
     Jefferson MO-Lincoln MO-Madison MO-Moniteau MO-Montgomery
     MO-Osage MO-Reynolds MO-Saint Charles MO-Saint Francois MO-
     Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-
     Warren MO-Washington MO.

IL...Dense Fog Advisory until 10 AM CST Monday for Bond IL-Calhoun IL-
     Clinton IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
     Madison IL-Marion IL-Monroe IL-Montgomery IL-Randolph IL-
     Saint Clair IL-Washington IL.

&&

$$

WFO LSX



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