Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 191223

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
623 AM CST Thu Jan 19 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 359 AM CST Thu Jan 19 2017

An elongated disturbance over the plains will slowly lift towards
the upper Great Lakes today and tonight, spreading showers and
isolated thunderstorms into MO/IL.


.LONG TERM...  (Friday through Wednesday)
Issued at 359 AM CST Thu Jan 19 2017

The extended forecast features unseasonably warm temperatures and
an active upper air pattern. Startlingly good agreement is noted
between the GFS and ECMWF (through ~150 hrs) for the third day in
a row.

A compact disturbance reaches NM/TX/OK late Thu night, then
intensifies and lifts northeastward through the plains on Fri/Fri
night. Despite a potent upper vort max and favorable H7-H5 lapse
rates across the area on Fri evening, no pcpn is expected attm due
to limited moisture.

Another disturbance reaches the California coast on Friday and
develops into a large low pressure system over TX/OK on Saturday
night. The system begins to occlude and shifts eastward over the
southeastern CONUS on Sun/Sun night. Showers and isolated
thunderstorms associated with this system may affect the LSX CWA
from Saturday night through Sunday night.

Yet another disturbance reaches the west coast on Sunday night
and eventually induces a surface reflection over the plains by
Monday night. After a brief period of upper ridging across MO/IL,
this feature is forecast to lift towards the Great Lakes during
the early and middle part of next week, bringing a chance of rain
to the area.



.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 612 AM CST Thu Jan 19 2017

IFR ceilings present at KCOU will spread steadily north and east
with KSTL metro TAF sites seeing them by around 18Z and KUIN by
21Z. IFR ceilings will then last through this TAF period at all
sites. Light showers will last through the morning at KSTL and
KUIN sites as well, with an isolated thunderstorm possible. Visibilities
will then likely drop to IFR in fog overnight at KUIN and metro
KSTL TAF sites. Light southeast winds today will become variable

SPECIFICS FOR KSTL: MVFR ceilings will drop to IFR status by
around 18Z and remain there through this TAF period. Light showers
will last through around 23Z or so, with an isolated
thunderstorm possible this afternoon. Visibilities will also drop
into IFR range overnight with light nad variable winds.





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