Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 231130 AAB

Area Forecast Discussion...UPDATED
National Weather Service Saint Louis MO
630 AM CDT Sun Apr 23 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 315 AM CDT Sun Apr 23 2017

Ridge axis extending across north central Kansas into central Iowa
will drift southeast into the area today.  North-northeast flow will
prevail ahead of the ridge continuing to provide weak cold
advection.  Regardless...full sunshine and and strong late
April insolation will warm our early morning lows from the low to
mid 40s up into the upper 60s and lower 70s this afternoon.  The
ridge will continue drifting east tonight.  Wind will turn around to
the south over central and northeast Missouri as well as west
central Illinois tonight.  Lows tonight will be a little tricky
due to the wind shift.  Aforementioned areas may see lows around
midnight with steady or slowly rising temperatures toward morning
while the remainder of the area may have a more normal diurnal
temperature curve.  It does look like lows will be a bit warmer on
Monday morning across the area due to the warmer start to the
evening.  Generally stuck pretty close to MOS guidance...though I
did knock a few degrees off temperatures in river valleys due to
light wind and clear sky resulting in excellent radiational cooling


.LONG TERM...  (Monday through Saturday)
Issued at 315 AM CDT Sun Apr 23 2017

Closed upper low that will be over the southeast CONUS early on
Monday morning will move offshore and up the East Coast by midweek.
In the meantime, what will start out as quasi-zonal flow over the
western two-thirds of country will amplify as a trough enters the
western CONUS on Monday and deepens into a longwave over the central
Plains by Wednesday.  Ahead of this trough, Monday and Tuesday still
look warm and dry as the upper flow turns out of the southwest and
850mb temperatures climb into the 10-15C range.  There is relatively
good agreement between the GFS/ECMWF/Canadian that a cold front will
move through MO/IL ahead of this trough on Wednesday. GFS and ECMWF
are showing enough instability and shear for a few organized
thunderstorms on Wednesday as the front moves through the area.

The front will move east of the area by Wednesday night and a
surface high will move across the area on Thursday.  Temperatures
will be cooler with 850mb temperatures only around 5C with a slight
chance of showers and thunderstorms as both GFS/ECMWF show a weak
shortwave moving across the Midwest.  Better chance of showers and
thunderstorms will come by next Friday and Saturday when a deeper
closed low will set up over the southwestern CONUS.  This will cause
low pressure to deepen over the Plains and a warm front to move
north into Missouri and Illinois by Friday night.  Showers and
thunderstorms will start over the Missouri and Illinois ahead of the
warm front on Thursday night and Friday as strong low level moisture
convergence sets up on the nose of a low level jet.  The GFS/ECMWF
shows the warm front moving into the region by next Saturday with
the chance of thunderstorms continuing.



.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 625 AM CDT Sun Apr 23 2017

High pressure will control the weather today and tonight. North-
northeast flow and VFR flight conditions will prevail today with
light and variable wind tonight...turning to the southeast late
tonight over central and northeast Missouri as well as west
central Illinois as the ridge axis moves through.


VFR flight conditions and north-northeast flow will prevail at
Lambert through the evening. There may be an occasional wind gust
to around 15kts this morning, but gusts should subside by early to
mid afternoon. VFR conditions will continue tonight...and the wind
will become light and variable, then turn to the southeast on
Monday morning as the ridge axis moves east of the terminal.





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