Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 181058

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
458 AM CST Tue Dec 18 2018

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 320 AM CST Tue Dec 18 2018

Latest surface analysis was showing a 1026mb surface high over the
western Great Lakes with a ridge extending southward into Illinois
and southeast Missouri.  Scattered-broken high clouds were spreading
across the area ahead of a mid level shortwave that the GFS/NAM
shows moving northeast across the CWA late this afternoon and early
this evening.  Temperatures early this morning ranged from the mid
20s to the mid 30s.

The high clouds will move out of the area this afternoon which will
provide for decent solar insolation.  Despite this, forecast RAP
soundings are only showing mixing up to 950mb, so will keep highs
ranging from the upper 40`s to mid 50`s today.  There will be some
increase in clouds and wind tonight, particularly over the western
half of the CWA, so kept highs in the 30`s.

Wednesday is expected to remain dry except late in the afternoon
over central and northeast Missouri.  A shortwave ridge will move
across the area late tonight into early tomorrow which will act to
suppress any precipitation.  By afternoon, an approaching upper
trough in tandem will increasing low level convergence to bring a
chance of rain over central and northeast Missouri.

Highs on Wednesday will reach into the lower to middle 50s ahead of
a cold front that will move into the western Missouri late in the


.LONG TERM...  (Wednesday Night through Monday)
Issued at 320 AM CST Tue Dec 18 2018

(Wednesday Night - Thursday Night)

A cold front is expected to be nearing the northwestern CWA border
early Wednesday evening. The chances of light rain will be on the
increase behind this front as a midlevel shortwave trough amplifies
across the lower Mississippi Valley. Much of the CWA will also be
beneath the right-entrance region of an upper-level jet streak
located near the western Great Lakes helping to providing an
additional source of lift. Light rain should slowly translate
eastward with time Thursday afternoon and evening as the surface
front continues to progress into the Ohio Valley along with the
better forcing aloft. Surface temperatures will be dropping into the
mid to upper 30s toward the end of the precipitation so a few
snowflakes may briefly mix in with the light rain before the
precipitation shuts off. No accumulations of snowfall are expected
however at this time.

(Friday - Monday)

Zonal flow aloft will become established by early this weekend and
will prevail into early next week across the CONUS. Zonal flow is
notoriously difficult to pin down the timing and track of individual
shortwave troughs. Because of the uncertainty, there are no
mentionable PoPs with this forecast package. However, there is a
faint signal for a period of light rain and/or snow sometime this
weekend for northern sections of the forecast area. If confidence
increases in subsequent forecasts, PoPs may need to be introduced.

Temperatures in the extended portion of the forecast will likely be
near to slightly above normal for mid/late December. Lows are
forecast to generally be in the 20s to low 30s, with daytime highs
in the 30s and 40s.



.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 450 AM CST Tue Dec 18 2018

Dry and VFR conditions are expected through the end of the period.
Light and variable winds will turn out of the south to southeast
and remain under 10 knots.


Dry and VFR conditions are expected through the end of the period.
Light and variable winds will turn out of the south to southeast
and remain light.





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