Area Forecast Discussion
Issued by NWS St. Louis, MO

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775
FXUS63 KLSX 222323
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
623 PM CDT THU SEP 22 2016

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 335 PM CDT Thu Sep 22 2016

The synoptic pattern this afternoon features a strong trough digging
into the western CONUS, with downstream ridging in place across the
southern and central US.  This regime will change little through the
short term period, keeping warm and dry conditions in place.

A remnant outflow boundary, now serving as an effective stationary
front, currently resides across portions of central IA (as seen on
DMX radar).  Showers and a few storms continue to form along and
especially to the north of this boundary.  Some hi-res guidance
wants to bring a few of these showers into northeast MO or west-
central IL this evening into tonight.  However, given the northern
location of the boundary and the lackluster thermodynamic
environment in place over the LSX CWA, see little reason any
precipitation will make it this far south. Thus have continued with
a dry forecast tonight. Overnight lows will be similar to the last
couple of nights with temps dipping in the low/mid 60s.

Friday will be almost a carbon copy of today.  Similar low-level
thicknesses and expected mixing heights puts highs very similar to
today`s values, in the upper 80s and low 90s.  It will once again be
a dry day with any precipitation expected to remain off to the north
and west.

KD

.LONG TERM...  (Friday Night through Next Thursday)
Issued at 335 PM CDT Thu Sep 22 2016

Backdoor type cold front will drop south-southwestward Friday night
and Saturday with surface ridging over the Great Lakes region, but
it appears that it will stay just northeast of our forecast area
with no significant impacts on our weather.  The unseasonably warm
weather pattern will continue into the weekend with upper level
ridging over the region and persistent southerly surface/low level
winds.  Showers and storms should move into northeast and central
portions of MO by late Saturday night as an upper level trough moves
eastward through the northern Plains and the upper level ridge
begins to shift southeast of our area.  Upper level divergence will
be increasing over this area ahead of the approaching upper level
trough.  A cold front will drop southeastward through our forecast
area Sunday and Sunday night with at least scattered showers and
storms expected along this front. The NAM model appears a little too
fast with the southeastward progression of this front and prefer the
slower timing of the GFS and ECMWF models.  Cooler temperatures are
expected Sunday night and Monday due to cold air advection behind
the cold front along with falling upper level heights.  The GFS
model is deeper with the upper level trough compared to the ECMWF
model and also cooler with the 850 mb temperatures leading to a
cooler solution on Monday.  Will forecast below normal temperatures
across northeast and central MO and west central IL on Monday, with
near normal temperatures further southeast.  Most of the
precipitation should shift southeast of our forecast area by Monday
night as a surface ridge builds southeastward into the area behind
the cold front.  The GFS model has lingering precipitation across
southeast MO and southwest IL Monday night due to its deeper and
slower upper level trough compared to the ECMWF model.  A dry and
relatively cool period is expected for Tuesday through Thursday due
to northwest upper level flow with an upper level trough/low
centered over the Great Lakes region and surface ridging over the
area.

GKS

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 620 PM CDT Thu Sep 22 2016

Radiational fog will be possible once again overnight into early
Friday morning at KSUS and KCPS, where visibilities could at times
could be in the IFR range. Otherwise and elsewhere, VFR flight
conditions are expected to dominate throughout the forecast
period.

SPECIFICS FOR KSTL:

VFR flight conditions are expected to prevail throughout the
forecast period.

Glass

&&

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

$$

WFO LSX



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