Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 211731

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1231 PM CDT Mon May 21 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 321 AM CDT Mon May 21 2018

Weak low pressure centered between Moberly and Chillicothe will
drift northeast into northern Indiana or southwest Michigan over the
next 24 hours.  The trailing cold front should work its way slowly
southeast through the forecast area during this time.  Timing is
somewhat uncertain for FROPA as upper level forcing is fairly weak.
However, there will be a definite airmass change as dew point
temperatures in the "cool sector" of this system drop into the
mid and upper 50s over the central Plains and Iowa. Not sure it
will get quite that dry over central and eastern Missouri into
central and southern Illinois, but the FROPA should scour out
enough moisture to bring an end to this most recent period of wet
weather. However scattered showers and thunderstorms will continue
to be possible at almost any time until the front finally passes
through the area this evening. Highs this afternoon will be highly
dependent upon any convection that forms, but temperatures will
most likely be very similar to Sunday`s highs in the upper 70s to
low 80s.


.LONG TERM...  (Tuesday through Sunday)
Issued at 321 AM CDT Mon May 21 2018

Global models are in reasonable agreement that an upper level ridge
will slowly move across Missouri and Illinois from Tuesday into
Thursday.  At the same time, a surface high will move east from
Minnesota into Michigan as an associated surface ridge slowly
pivots over Missouri and Illinois. This pattern will keep dry
weather across our area Tuesday into Wednesday. Moisture will
begin to return on the back side of the ridge over central and
northeast Missouri and west central Illinois by Thursday bringing
a slight chance of showers and thunderstorms to these areas. The
chance of showers and thunderstorms will increase areawide Friday
into next weekend when the GFS/ECMWF/Canadian all show a trough
and an attendant cold front moving across Missouri and Illinois.

Temperatures are still expected to be above normal through the
period.  850mb temperatures support highs staying 5-10 degrees above
normal for late May.



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1223 PM CDT Mon May 21 2018

A brief period of MVFR ceilings are likely early this afternoon
before they lift toward low VFR. Trailing cold front will try and
initiate widely scattered showers and thunderstorms but most
activity looks east of the Mississippi River. Left in VCTS in for
metro terminals as they will be on western edge of activity.
Models hinting at MVFR ceilings again late tonight into early
Tuesday morning, with fog also a possibility where more clearing
is observed.


MVFR stratus to continue early this afternoon before lifting. Kept
a VCTS group in for late afternoon as widely scattered showers and
storms are still possible along a slow moving cold front. Another
round of MVFR stratus possible late tonight/early Tuesday morning
but not confident enough to mention explicity. Cloudiness should
decrease by late Tuesday morning leaving a mostly sunny sky with
light north/northeast winds.





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