Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 241739

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1239 PM CDT Mon Apr 24 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 254 AM CDT Mon Apr 24 2017

Ridge axis extending from west central Illinois through central into
southwest Missouri will drift eastward today.  Wind will turn to the
south-southeast after the ridge axis passes and Warm advection
will allow temperatures to rise above yesterday`s highs. 850mb
temps between 12 and 14 degrees mix down to mid 70s to around 80
this afternoon. This looks reasonable given the warm April
sunshine and yesterday`s temperatures in the low to mid 70s so
stuck pretty close to warm MAV guidance today. Southerly flow will
continue tonight which should continue the warming trend.
Overnight lows MOS guidance lows in the upper 40s to low 50s look
reasonable with slightly warmer temperatures in the urban areas of
St. Louis.


.LONG TERM...  (Tuesday through Sunday)
Issued at 254 AM CDT Mon Apr 24 2017

Still looks like it will be an active weather week for showers and
thunderstorms through next weekend with the potential for a few
strong to severe thunderstorms and the potential for an additional 2-
5+ inches of rainfall by Sunday.

Upper trough entering the Pacific northwest today will deepen over
central Plains by Wednesday.  We will still see low level flow turn
out of the south ahead of it on Tuesday with 850mb temperatures
climbing to around 15C.  Highs near 80F still look good tomorrow
afternoon.  The chance for showers and thunderstorms will increase
late Tuesday night into Wednesday as both the GFS/ECMWF are showing
strong low level convergence developing along and ahead of the cold
front beneath strong mid-upper ascent ahead of the upper trough.
Could be a few strong or severe thunderstorms ahead of the cold
front given MLCAPEs of 1000-2000 J/kg and deep layer shear around
50+kts. Heavy rainfall will also be possible given PWATS over 1.5
inches and the potential for training cells.

Rain chances will continue into Wednesday night and early Thursday
as the upper trough will not exit the area until midday.  After a
brief break in the rain chances late week as a weak shortwave ridge
moves across the area, showers and thunderstorms will return by
Friday night.  This is when the GFS/ECMWF shows the front returning
back north as a warm front.  There should be a strong low level
moisture convergence on the nose of 40kt low level jet which will
produce showers and thunderstorms Friday night into Saturday.  The
warm front will move slowly north into the CWA on Saturday and
Saturday night as the upper low over the southwestern CONUS moves
east into the Plains.  A surface low will move northeast out of the
Plains on Saturday into the Midwest on Sunday bringing a cold front
across the area on Sunday. Both the GFS/ECMWF are showing sufficient
instability and shear for additional strong thunderstorms.   In
addition, shear vectors will be aligned for training storms with
both the GFS and ECMWF showing the potential for locally heavy
rainfall over the weekend.

After a brief cool down with highs only in the 60s on Thursday with
850mb temperatures only around 5C, temperatures will climb back up
above normal next weekend in the warm sector with 850mb temperatures
around 15C.



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1237 PM CDT Mon Apr 24 2017

VFR and dry thru the TAF period. Sely winds will increase on
Tues morning with gusts around 20 kts.





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