Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 221735

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1235 PM CDT Sat Apr 22 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 339 AM CDT Sat Apr 22 2017

One wave of rain will move out of the area around 10z while the next
wave moves into central MO. Previous forecast has a decent handle on
the situation however have had to manipulate the pops a bit to try
and match the movement. Temperatures will be quite cool today, but
have raised the highs just a bit for most areas. The upper system
finally moves out late tonight from 06 to 12z Sunday. Rain will end
this evening hanging on the longest across the southeast. Plenty of
dry air, sunshine, and warmer temperatures for Sunday.


.LONG TERM...  (Sunday through Friday)
Issued at 339 AM CDT Sat Apr 22 2017

After a chilly start to Sunday morning strong April sunshine under a
mostly clear sky should kick temperatures back up into the upper 60s
and low 70s in spite of continuing weak north-northeast flow and cold
advection.  Tranquil weather continues Sunday night through Monday
night with temperatures warming well into the 70s on Monday as warm
advection ramps back up ahead of a trof of low pressure over the
Great Plains.

The cold front associated with this trof will move into southeast
Nebraska or northwest Missouri on Tuesday.  There`s some
discrepancies between model guidance on the timing and strength of
the system as it pushes further east through Missouri on Tuesday
night.  It does look like we`ll see some thunderstorms Tuesday night
across the area.  GFS has MUCAPE over 500 J/Kg all the way up into
west central Illinois at 06Z with showalter index around -3...though
the greatest instability will stay south of I-70 across southeast
Missouri and southwest Illinois with MUCAPE in excess of 1000 J/Kg.
0-6km shear is 40-50kts and the greater instability across the
Ozarks suggests there could be some strong to severe storms. However
the ECMWF is has even less CAPE than the GFS and would suggest that
severe potential would be very limited if any at all Tuesday night.
The ECMWF is also quite a bit faster pushing the front through and
would basically have us in dry/cold advection all day Wednesday
while the GFS pushes the front through our area during the morning
and early afternoon on Wednesday and therefore has much more
precipitation over us.  Tuesday continues to look warm ahead of the
front int warm advection. Think upper 70s and low 80s is easily
attainable in southwest flow. Wednesday should be cooler whether due
to clouds and precip or due to cold advection.

The GFS drops another strong longwave trof of low pressure over the
Rockies on Thursday.  The ECMWF handles this trof differently with
an initially weaker shortwave and then the stronger longwave
developing late in the forecast on Friday.  Either way, the weather
on Thursday and particularly Friday looks unsettled although
confidence is low due to the model differences that far out.



.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1230 PM CDT Sat Apr 22 2017

Light rain shield should stay south of the terminals though cannot
rule out some brief light rain or sprinkles for the metro
terminals. Sky cover should decrease late this afternoon and
tonight with a clear sky expected by midnight. Gusty northeast
winds should lighten up by early this evening with predominant
winds becoming more northerly as well. Clear sky with light
northerly winds for late tonight/Sunday.


VFR with small chance of a brief period of light rain and/or
sprinkles. Gusty northeast winds lightening up and becoming more
northerly by this evening. Continued VFR/quiet through Sunday with
a clear sky and light northerly winds.





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