Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 222305

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

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 344 PM CDT Sat Apr 22 2017

Mid/upper level low is slowly moving southeastward early this
afternoon and will move away from the area tonight. Lingering area
of light rain currently over portions of southeastern Missouri and
southwestern Illinois will slowly move out of the area late this
afternoon and early this evening. Otherwise, expect decreasing
cloudiness which combined with fairly light north/northeast winds
should yield a seasonably cool night. Forecast lows range from the
upper 30s to low 40s across the area which is just a tad below MOS
numbers. Cannot rule out some patchy frost either in sheltered
valley locations.

Pleasant day is still on tap for Sunday as sfc ridge slides across
the bi-state area. Look for highs mainly in the low 70s along with
plentiful sunshine.


.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 344 PM CDT Sat Apr 22 2017

Another relatively cool night expected Sunday night with good
radiational cooling near the surface ridge axis due to a clear sky,
light surface wind, and fairly low surface dew points.  Warmer
temperatures are forecast for Monday as the surface/low level winds
become southerly as the surface ridge shifts east of the region.  A
southerly low level jet will being increasing low level moisture
into the area on Tuesday with a continued warming trend and
gradually rising surface dew points.  Convection will shift
southeastward into the forecast area Tuesday night as upper level
divergence increases ahead of an approaching upper level trough, and
a cold front drops southeastward into our area.  The ECMWF model is
a little slower with the progression of the upper level trough and
associated cold front versus the GFS and keeps the threat for
convection going through Wednesday night, while the GFS shifts the
precipitation southeast of the forecast area by Wednesday evening.
For now will lean towards the faster GFS model solution and drop the
pops Wednesday night.  Cooler temperatures are expected Wednesday
night and Thursday with a surface ridge building southward into the
region from the northern Plains behind the cold front.  Model
solutions begin to diverge on Thursday leading to a low confidence
forecast for the end of the work week and into the weekend.  The GFS
model is much wetter than the ECMWF model for Thursday afternoon
through Friday night with an active southwest upper level flow and a
nearly stationary front across our forecast area leading to several
rounds of convection.  The ECMWF model keeps surface ridging locked
into our area from the northern Plains and Great Lakes region,
keeping most of the shower/thunderstorm activity south and west of
the forecast area until Saturday when convection spreads into the
forecast area ahead of an approaching upper level low and surface
low in the central Plains.  For now will lean toward the GFS
solution and ramp the pops up Thursday afternoon and evening and
continue at least chance pops for most of the area through the
remainder of the forecast.



.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 559 PM CDT Sat Apr 22 2017

VFR through the period. Initially gusty northeasterly winds at
TAF issuance will diminish after sunset. Wind speeds will become
light due to the approach and passage of a surface ridge axis.





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