Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 010813
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
313 AM CDT SAT OCT 1 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 311 AM CDT Sat Oct 1 2016

The synoptic pattern early this morning features a stubborn,
vertically-stacked low spinning over the Ohio River near the
IN/OH border. This system will be the main focus of the short term
period.

The broken record of a cool, gloomy, and damp forecast will persist
today. Several vort maxes continue to traverse around the periphery
of the upper-level low, each helping to spark shower activity.  One
such wave is currently located across eastern IL, which will rotate
westward this morning into west-central IL. This will bring a round
of scattered showers mainly across IL and extreme eastern MO through
the mid morning hours. Additional diurnally-driven showers will be
possible through this afternoon into the early evening hours (again
mainly over western IL/extreme eastern MO), but as the upper-level
low begins to push to the northeast, expect synoptic-scale lift to
decrease and shower coverage to diminish by this evening.  Given a
very similar pattern to yesterday, went with a persistence
temperature forecast which puts highs in the upper 60s/low 70s.

For tonight, while some patchy drizzle may still persist in a few
locations, expect a drying trend as the upper-level low shifts
northward.  However, copious low-level moisture will lead to low-
level cloud cover sticking around through the overnight hours,
especially north of I-70.  Overnight lows will dip into the
mid/upper 50s.

KD

.LONG TERM...  (Sunday through Friday)
Issued at 311 AM CDT Sat Oct 1 2016

The synoptic pattern at the start of the long term period will
feature what was a closed upper-level low over the Great Lakes,
opening up into a progressive wave.  Upstream, a longwave trough
will build into the northwestern CONUS.  This approaching west coast
trough will be the main focus of the long term period.

The upper-level low will finally push well off to the northeast of
the region by Sunday as it transitions into an open wave and gets
ingested into the upper-level flow. However, the region will still
remain within cyclonic flow aloft, with some guidance suggesting a
weak PV anomaly diving southeast through the flow.  Weak
surface ridging will build into the Midwest, but guidance suggests
copious low-level moisture will still be in place.  Given the lack of
good boundary-layer mixing and the cyclonic flow aloft, agree with
the previous forecaster in keeping widespread cloud cover in for
Sunday.  In fact, some of the latest guidance suggests that synoptic
ascent from the weak PV anomaly may even be enough to squeeze out a
few light showers on Sunday.  Given the moisture profile looks fairly
shallow on forecast soundings, will leave the forecast dry for now,
but this is something to monitor in future forecasts.

The cloud cover should finally scatter out for Monday as upper-level
ridging builds in ahead of the western trough.  Guidance differs a
bit on how the trough will eject out into the Plains, with the ECMWF
suggesting a sharper, more neutral/slight negative tilt trough and
the GFS/GEFS mean suggesting more of a broad trough.  This
difference causes a stronger/more progressive solution on the ECMWF
as it blasts the surface front through the region, while the GFS is
slower with the front as a couple weaker waves ride along it.  For
now, will go with a general guidance blend until there is better
agreement in solutions.

KD

&&

.AVIATION...  (For the 00z TAFs through 00z Saturday Evening)
Issued at 958 PM CDT Fri Sep 30 2016

Low level clouds along with scattered showers continue to rotate
through eastern MO and IL on the backside of the slow moving upper
level and surface low over southern IN. Most of the showers should
be east of the taf sites late tonight, although could not rule out
a brief light shower or a little drizzle in UIN and the St Louis
metro area. The cloud ceiling will gradually lower overnight into
the MVFR catagory in COU and into the IFR catagory in UIN and the
St Louis metro area. The cloud ceiling should gradually rise into
the VFR catagory by late Saturday afternoon with daytime heating
and mixing and deepening of the boundary layer. May be a few
showers Saturday afternoon in UIN and the St Louis metro area.
North-northwesterly surface winds will continue through the
period.

SPECIFICS FOR KSTL: Low level clouds along with scattered showers
continue to rotate through eastern MO and IL on the backside of
the slow moving upper level and surface low over southern IN. Most
of the showers should be east of the taf sites late tonight,
although could not rule out a brief light shower or a little
drizzle in the STL area. The cloud ceiling will gradually lower
overnight into the IFR catagory in STL. The cloud ceiling should
gradually rise into the VFR catagory by late Saturday afternoon
with daytime heating and mixing and deepening of the boundary
layer. May be a few showers Saturday afternoon in STL. North-
northwesterly surface winds will continue through the period.

GKS

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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