Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 260243
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
943 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 00z TAFs through 00z Monday Evening)
Issued at 601 PM CDT Sun Sep 25 2016
The cold front has passed through all of the terminals was located
across southeast MO and southwest IL at 23Z. Any threat of thunderstorms
is rather low although will need to keep an eye on the few storms
southwest of KVIH. The threat of precipitation however is no over
and it appears that later this evening a band of post-frontal
showers/rain will develop across parts of central and eastern MO.
This should impact the St. Louis region terminals overnight but I
don`t think there will be any lasting visibility restrictions or
dramatic lowering of flight categories, with predominately VFR. I
have lesser confidence in any showers/rain at KCOU or KUIN. Clear
skies/VFR expected on Monday with modest northwest winds and
SPECIFICS FOR KSTL:
The cold front has passed through KSTL and any threat of thunderstorms
is rather low, although will need to keep an eye on the few storms
southwest of KVIH this evening. It appears that later this evening
a band of post-frontal showers/rain will develop across parts of
central and eastern MO and impact KSTL overnight. I can`t rule out
conditions briefing falling to MVFR in the rain/showers, however I
think flight conditions will be predominately VFR. Clear skies/VFR
expected on Monday with modest northwest winds and gusts to 20 kts.