Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 210823

Area Forecast Discussion
National Weather Service Saint Louis MO
323 AM 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 06z TAFs through 06z Monday Night)
Issued at 1150 PM CDT Sun May 20 2018

Showers will continue pushing northeast through the bi-state
region tonight with embedded thunderstorms. Locally heavy rain is
possible, but thunderstorm intensity will trend downward. Expect
MVFR cigs in the 3k-5k ft range to accompany this activity. Vsby
may briefly drop below 6SM, but will become less common as the
complex weakens.

The main front remains to the west. There may be patchy areas
where cloud break, mainly near KCOU, where cigs could flirt with
IFR. Any opportunity would only last a few hours. The front pushes
east during the day with a few showers possible along the front. A
few thunderstorm could pop during the afternoon, but should be
clear of the TAF sites by the time enough heat builds to result in
afternoon storms.


Showers and thunderstorms will continue through the next couple of
hours before moving northeast by early morning. A few showers may
linger with MVFR cigs improving back to VFR through the early
morning timeframe. The main front will push through during the day
Monday. Showers are possible along the front, especially during
the afternoon. The better chances will line up east of KSTL with
quieter conditions expected through late Monday. VFR conditions
are forecast through the period. MVFR cigs should remain well
north and west of the site, barring any showers directly impact
KSTL Monday afternoon.





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