Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 260448

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1148 PM CDT SUN SEP 25 2016

Issued at 938 PM CDT Sun Sep 25 2016

Already made some updates much earlier this evening and those
trends are shaping up. The cold front has become more NE-SW
oriented across southwest IL and southeast MO this evening and
there has been some recent development of scattered thunderstorms
along it. Meanwhile one small weakening cluster of showers and a
little thunder which is actually on the cool side of the boundary will
move thru metro St. Louis before midnight.

The biggest change to the earlier forecast was the realignment of
pops late this evening and overnight. Low-mid level frontogenesis
is increasing through central MO as well as large scale forcing
associated with the short wave trof swinging through the midwest.
This is resulting in a expanding band of showers/rain centered
through central MO. Growth and increasing coverage of this band
should continue overnight as it moves to the east/southeast.



.SHORT TERM...  (Through Late Tonight)
Issued at 325 PM CDT Sun Sep 25 2016

A cold front extending from just west of UIN southwest to near COU
will continue moving southeastward tonight.  Widely scattered
showers and storms have developed ahead of the front this afternoon,
mainly across parts of southeast MO and southwest IL.  Much of this
convective activity should shift southeast of our forecast area
early this evening, but there should be some post frontal light
showers or rain moving through our area tonight as a deepening upper
level trough with embedded shortwaves moves eastward through the
northern Plains and into the Great Lakes region.  Cooler and less
humid air will filter southeastward into the region tonight behind
the cold front as a large and strong surface ridge builds east-
southeastward into our area.


.LONG TERM...  (Monday through Next Sunday)
Issued at 325 PM CDT Sun Sep 25 2016

The synoptic pattern at the start of the long term period will
feature an upper-level low digging into the north-central CONUS.
This upper-level low will slowly meander to the ESE along the
eastern seaboard through the end of the period, becoming closed off
from the better upper-level flow which will help to set up a
blocking pattern across much of the CONUS into the upcoming weekend.

The cold front will have pushed to the southeast of the region by
Monday morning, ending the precip chances.  Surface ridging will
build into the Southern Plains, which will place eastern MO/western
IL in a fairly tight pressure gradient due to deepening low pressure
across the northern Great Lakes.  Forecast soundings show mixing to
about 850mb, where 25 knots of flow will exist.  Therefore, think it
will be fairly breezy tomorrow, especially across northern MO with
sustained winds around 15 to 20 mph with gusts to around 25 mph.

Otherwise, expect surface ridging to dominate the upcoming week.
This will keep dry and seasonably cool conditions in the forecast
through the period.  Look for highs generally in the low to mid 70s,
with overnight lows in the upper 40s to low 50s.



.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1142 PM CDT Sun Sep 25 2016

A band of rain/showers will shift from central and eastern MO
eastward overnight and should exit to the east of the St. Louis
region by 10Z. Flight conditions will be predominately VFR
although the St. Louis area could see MVFR flight conditions for
the first part of the valid TAF period. Clear skies/VFR expected
on Monday with modest northwest winds and gusts 15-20kts.


Rain/showers are expected through around 10z. Flight conditions
may periodically be in the MVFR flight category early in the
valid TAF period, however VFR flight conditions are largely expected
with the precipitation. Clear skies/VFR expected on Monday with
modest northwest winds and gusts 15-20kts.





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