Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 132146
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
346 PM CST Fri Jan 13 2017

.SYNOPSIS...
Issued at 340 PM CST Fri Jan 13 2017

No major changes to the forecast. Headlines and ice storm warnings
continue into Sunday. Thus far highest ice accumulations reported
across parts of southeast MO and far southwest IL nearing .20
inches. Overall storm total ice accumulations of 0.25 to 0.50 and
locally higher still appear on track.

Glass

&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 340 PM CST Fri Jan 13 2017

Focus thru this period continues to be the impending icing event.

Sfc ridge currently over the Great Lakes region will continue to
build ewd this evening. In the wake, another reinforcing sfc ridge
develops over the nrn Plains due to the snow pack over this region
as temps drop tonight.

Do not expect temps to move much tonight other than dropping a
couple of degrees after sunset. Also do not expect temps to change
much on Sat. Some locations may see a max temp on Sat of a degree or
two above freezing, but any temps above freezing shud be short
lived.

As for precip chances, ongoing FZRA will continue to move ewd this
evening. Expect more of a lull in precip activity tonight. This
creates a message issue with more shower activity expected tonight,
but it appears to be a high probability of it occurring. Have
therefore kept PoPs in the likely range thru much of the night.
Precip shud remain light thru much of the night with an increase in
intensity possible late tonight thru early Sat morning. There
appears to be two main areas of precip expected late tonight into
the morning, one across the mid to srn portions of the CWA and the
other across the nrn portions. initially, this more nrn area of
precip was expected to be light shower activity. However, the 13/18z
NAM, which is just arriving, wud suggest this area of precip may be
heavier than prev anticipated.

After this first wave of precip late tonight thru early Sat morning,
expect precip coverage to increase mid to late Sat morning, mainly
across srn portions of the CWA. With these warmer temps, albeit only
slightly warmer, do not anticipate much additional ice accumulation
across this area.

Overall, not a lot of change in the going forecast for ice
accumulation amounts at this time.

Tilly

.LONG TERM...  (Saturday Night through Next Friday)
Issued at 340 PM CST Fri Jan 13 2017

A wave of more significant precipitation should spread into the
area from the west/southwest on Saturday night. This will be in
response to another impulse in the flow aloft and associated
forcing, as well as increasing isentropic ascent due to backing of
the low level/H85 flow in response to this impulse. Waves of
precipitation will continue on Sunday in response to yet another
impulse aloft and continued low-level WAA/isentropic ascent. The
overall precipitation shield should shift northward with time, due
to backing flow aloft, with the precipitation/freezing rain centered
thru northern MO and west central IL by the later part of the
afternoon.

Temperature tends continue to be the big question mark and in
general the models appear to be warming the surface temperatures
too quickly, especially the GFS. This forecast has trended a bit
colder for Saturday night into Sunday morning with clouds and
northeast surface winds/CAA at least maintaining the temps and
delaying the rise. The warm-up however should proceed on Sunday,
and primarily Sunday afternoon with only far northern MO and west
central IL remaining at or slightly below freezing at 00Z Monday.
On Sunday night the main focus of precipitation should shift to
primarily northern MO into the upper MS Valley in response to
continue backing flow aloft and a more decide southerly LLJ.
Increasing southeast surface winds should finally drive surface
temps above freezing across the remainder of the CWA by the
overnight hours.

Models diverge on Monday with the overall upper air pattern. The GFS
suggests a dominate northern stream upper low tracking across the
Midwest as a key player, while the ECMWF maintains the upper low
lifting northeast. The ramifications on this are the speed/timing/location
of the lifting associated surface low and cold front progression
across the area late Monday into Tuesday. The ECMWF has been most
consistent and has been followed most closely. Mild air will
overspread the area on Monday in advance of the cold front with
rain and isolated thunderstorms continuing along/ahead of the cold
front through Tuesday. Thereafter, an unseasonably mild pattern
appears on track the remainder of the week with temps some 20-25
degrees above normal.

Glass

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1144 AM CST Fri Jan 13 2017

Ongoing FZRA will continue thru this afternoon and is expected to
move nwd slightly. Expect precip to diminish late this afternoon
into the evening. Believe much of the precip tonight will be more
shower activity. However, as temps cool overnight, expect cigs to
lower as well as a threat of fog development and perhaps FZDZ. To
keep the TAF simple, just left as FZRA. Visbys may be lower than
current TAF due to fog developing, however, do not currently
expect it to cause a lower category than what the cigs will cause.
Precip shud move south of all terminals by mid morning or so.

Tilly

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Ice Storm Warning until 6 AM CST Sunday for Crawford MO-Iron MO-
     Madison MO-Reynolds MO-Saint Francois MO-Sainte Genevieve
     MO-Washington MO.

     Ice Storm Warning until 3 PM CST Sunday for Audrain MO-Lincoln
     MO-Monroe MO-Pike MO-Ralls MO.

     Ice Storm Warning until noon CST Sunday for Boone MO-Callaway MO-
     Cole MO-Franklin MO-Gasconade MO-Jefferson MO-Moniteau MO-
     Montgomery MO-Osage MO-Saint Charles MO-Saint Louis City MO-
     Saint Louis MO-Warren MO.

     Ice Storm Warning until 6 PM CST Sunday for Knox MO-Lewis MO-
     Marion MO-Shelby MO.

IL...Ice Storm Warning until 6 AM CST Sunday for Randolph IL.

     Ice Storm Warning until 3 PM CST Sunday for Calhoun IL-Greene IL-
     Jersey IL-Macoupin IL-Montgomery IL-Pike IL.

     Ice Storm Warning until noon CST Sunday for Bond IL-Clinton IL-
     Fayette IL-Madison IL-Marion IL-Monroe IL-Saint Clair IL-
     Washington IL.

     Ice Storm Warning until 6 PM CST Sunday for Adams IL-Brown IL.

&&

$$

WFO LSX



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