Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 172116

Area Forecast Discussion
National Weather Service Saint Louis MO
416 PM CDT Sat Mar 17 2018

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 415 PM CDT Sat Mar 17 2018

Low pressure moving into the Tennessee Valley will continue to drag
stratus southeast in its wake tonight. Meanwhile, guidance is
showing ridging building aloft and forecast soundings indicate a
strong subsidence inversion due to this ridge.  This indicates a
strongly stratified lower atmosphere.  This stratification will
likely allow little chance for the low level stratus deck to mix
out, especially given that our forecast area will remain in weak
cold advection at least into early Sunday morning.  Think the
blanket of clouds will limit cooling somewhat tonight...although the
northwest flow will make it a little chillier than this morning.
Stuck very close to the model consensus for lows for tonight.
However, with the thinking that those clouds will stick around for
much of the morning and perhaps into early afternoon, think the
colder side of guidance in the low to mid 50s for highs Sunday is


.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 415 PM CDT Sat Mar 17 2018

Weather for the remainder of the forecast will be dominated by two
systems.  The first is a shortwave that will eject eastward from the
large upper trof currently over the western U.S.  Models are showing
strong lee-side cyclogenesis late Sunday afternoon and Sunday night
as the wave moves off the Rockies into the Plains.  The surface
system is currently forecast to move through southern Kansas Sunday
night and east along the Missouri/Arkansas border on Monday.  All
guidance members show moderate to strong low level moisture
convergence ahead of the low along and south of I-70, wrapping back
around the low Monday afternoon into the early evening.  Likely to
categorical PoPs look appropriate fading to chance up across
northeast Missouri and west central Illinois.  Rain should end
Monday night as the system exits to the east.

Northwest flow aloft will persist over the Mississippi Valley for
the remainder of the week.  A couple of weak shortwaves move quickly
across the area in the northwest flow, which could produce light
rain first on Tuesday night and again on Thursday night into Friday.
Medium range guidance is disagreeing on timing and position of the
second strong system to affect the Midwest next weekend.  Current
thinking is that showers and thunderstorms will develop ahead of the
low either Friday or Friday night, but the timing differences
between the EC and GFS make this a low confidence forecast.



.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1235 PM CDT Sat Mar 17 2018

MVFR and IFR ceilings will continue to prevail across central and
eastern Missouri and west central and southwest Illinois at least
through tonight and into Sunday morning. IFR conditions are mostly
limited to northeast Missouri and west central Illinois at this
time...and some marginal improvement to low end MVFR is possible
this afternoon...but any improvement will likely be lost this
evening after sunset. There`s some potential for IFR to push
further south into central and east central Missouri later this
evening and tonight...though I`d like to see more agreement in the
guidance before forecasting IFR at KCOU or the STL Metro TAF
sites. Expect improvement in ceilings late in the
morning/afternoon on Sunday.


Expect MVFR ceilings to prevail at Lambert through Sunday morning.
While ceilings below 2000 feet are most likely through the`s possible the ceiling could lift to 2000-2500 briefly
this afternoon. Think any improvement will likely be lost after
sunset this evening. There`s some potential for IFR to push
further south tonight into the STL Metro area though I`d like to
see more agreement in the guidance before forecasting IFR at KSTL.
Expect the ceilings to lift and scatter Sunday afternoon.



Saint Louis     37  56  42  51 /   0   5  60  80
Quincy          32  52  37  50 /   0   5  10  40
Columbia        36  55  41  51 /   0  20  60  80
Jefferson City  36  56  42  52 /   0  20  70  90
Salem           35  55  40  52 /   0   5  50  80
Farmington      36  56  42  54 /   0  10  80  90




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