Area Forecast Discussion
Issued by NWS St. Louis, MO

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597
FXUS63 KLSX 141059
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
459 AM CST Sat Jan 14 2017

.SHORT TERM... (Through Sunday Night)
Issued at 318 AM CST Sat Jan 14 2017

No changes to existing headlines.

A wave of freezing rain was moving across the area early this
morning. Temperatures were in the upper 20s to lower 30s across
the region on the cold side of a stalled boundary which stretched
from AR into TN. Heavier rain rates were observed from time to
time at the NWS office overnight when stronger radar echoes moved
overhead, which is consistent with the +2 SD PW values depicted by
model guidance. Ice accretion is known to be less efficient with
heavier rain rates compared to lighter rain rates, and this may
cause some locations to receive slightly less ice accretion than
would otherwise be expected based solely on a look out the window.

A lull in the rain is expected this afternoon and early this
evening before the next wave of rain develops and spreads into
the area after midnight. The surface temperatures over parts of
southeast MO and southwest IL may have risen above freezing by
the time the overnight rain arrives, and for those locations the
freezing rain threat will have ended. Depending on the location
of the surface freezing line, future shifts may be able to end
the Ice Storm Warning early for some areas.

Temperatures are expected to rise above freezing across the
southern half of the CWA on Sunday. The combination of rising
temperatures and a northward shift of the precipitation axis will
end the threat of widespread freezing rain from south to north on
Sunday/Sunday night.

42

.LONG TERM... (Monday through Friday)
Issued at 318 AM CST Sat Jan 14 2017

A cutoff low near Baja California will rejoin the flow on
Saturday night in response to a shortwave diving down the West
Coast. The former cutoff low will lift northeastward into the
southern plains by 12z Monday. The sfc reflection of this feature
will lift the stalled boundary northward as a warm front on Sunday
night and Monday. Temperatures will warm well above freezing on
Monday within the warm sector. Instability may be sufficient for
isolated to scattered thunderstorms on Monday afternoon and
evening ahead of the system`s cold front.

Models diverge significantly by the middle of the week due to
differences in the speed, timing, location, existence of, and
interaction between several shortwaves.

42

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 445 AM CST Sat Jan 14 2017

Last wave of rain and freezing rain will likely end at KUIN and
KSTL metro TAF sites by around 15Z. KSTL temperature has been just
above freezing for several hours, so icing may not be an issue
there, however surrounding TAF sites are all still at or below
freezing so any precip that falls will be freezing rain. Most of
the day on Saturday should be relatively dry, but IFR ceilings
will persist at all but KUIN, and even there the ceilings will be
just above IFR status. Saturday night will see yet another round
of precip moving in, and all indications are that temperatures
will be close enough to 32F to yeild freezing rain. Ceilings
should improve to low end MVFR at all sites after around 00Z.
Winds will be light.

SPECIFICS FOR KSTL: Surface observations at KSTL ASOS have
remained at 33F for several hours, so any precipitation should be
rain. This wave of rain will likely end by around 14Z with IFR
ceilings continuing until after 00Z Sunday. Another wave of
precipitation will move in after 06Z and the temperature may fall
to 32F so have included -FZRA in the TAF, however would not be
surprised to see only rain. IFR ceilings should improve to low end
MVFR after around 02Z. Winds will remain light.

Browning

&&

.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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