Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 211012

Area Forecast Discussion
National Weather Service Saint Louis MO
412 AM CST Sat Jan 21 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 410 AM CST Sat Jan 21 2017

Two short waves will traverse the region thru the prd. The first will
lift N from wrn IA this mrng to wrn Lk Superior by tomorrow mrng.
The assoc SFC low will take a similar track which will lift a warm
from the IA/MN and IL/WI border this mrng into sthrn Canada by Sun
mrng. The nthwrd lifting wrm fnt will allow the low stratus across
nthrn MO to continue to slowly lift N today and keep SFC winds
Sthrly. The second short wave is expected to move almost due E from
the 4 Corners region this mrng to the Arklatex area by Sun mrng.

Deep SWrly flow between these systems...ample sunshine and decent
mixing for the time of season will help boost temps well into the
60s in most locations this aftn. The exception will be across NE MO
and W cntrl IL...where cooler 850 mb temps exist...temps are
expected to top out in the mid/upper 50s. The STL metro area may
crack 70 degrees...making a run at the record for the day which is
75 set in 1986. See the climate section below for the full list
of local records. Mid/high clouds will move into the FA from the
SW drng the aftn but think it will be late enough in the day not
to affect temps much.

Clouds will thicken and lower from late aftn into this evng. Rain
assoc with the sthrn stream short wave will move into the FA from SW
MO drng the evng. Precip is fcst to continue to overspread the CWA
tonight with the best coverage of precip along and S of I-70. There
could be a couple rumbles of thunder across SE and E cntrl MO and
sthrn IL. The rain is expected to continue into Sun. Despite the
rain...temps will remain in the 40s for most locations...which is
quite mild and is actually above the normal high for this time of


.LONG TERM...  (Sunday through Friday)
Issued at 410 AM CST Sat Jan 21 2017

A rather extensive shield of rain should extend from north of I-70
across southern MO and southern IL on Sunday morning, associated the
comma head of a prominent extratropical cyclone centered near the
central MO/AR border. This rain will be in response to large scale
ascent associated with the potent upper low located in the lower MS
Valley, and lift associated with the cyclonic branch of the warm
conveyor belt and the resulant mid level frontogenetical forcing.
The upper low and associated surface cyclone will track
east/northeast across the lower MS Valley into the TN Valley on
Sunday, bringing increasing/gusty northerly winds as the rain shield
shifts east and northeast across the southeastern 2/3rds of the CWA.
The low will then turn more northeast moving into the Mid Atlantic
region on Monday, with rain possibly continuing to effect portions
of far eastern MO into southwest IL during the evening hours on the
backside of the departing low. All of the precipitation is expected
to be well to the east by the time deeper cold air arrives in the
strong CAA regime. Monday will be a seasonably chilly day with gusty
northwest winds and extensive cloudiness through the morning hours.

Heights aloft will already be on the rise by Monday night as the
previous system departs and ridging begins to progress into the area
advance of the next upstream system. This next upper low/trof will
move through the Plains on Tuesday and into the MS Valley on Tuesday
night. Strong WAA in advance of the system should bring a nice temp
rebound for Tuesday with temps close to 15 degrees above average.
Moisture in advance of the system is quite limited and thus the
precipitation threat is atypically low for such a strong system and
largely confined to the northern CWA, closer to the track of
the surface low and where the greatest ascent is progged.

Broad cyclonic flow in the wake of this midweek system will bring
continued CAA along with another surge of colder air near the end of
the week. Several weak impulses in the flow aloft could also help
generate some light rain and/or snow in the Wednesday/Wednesday
night time frame for northern part of the CWA.



.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1136 PM CST Fri Jan 20 2017

Low clouds have finally exited the taf sites, so issue now is will
widespread fog develop. Feel that only KUIN could see MVFR vsbys
in fog through daybreak as cloud cover has just moved out in the
past hour. So kept mention in taf through the overnight hours.
Also, kept mention for some light fog at KSUS. Otherwise, south
winds to persist. Still some concern for LLWS as upper level jet
ramps up a bit, so kept mention in tafs. LLWS to diminish by
13z-14z timeframe.

Low clouds well north of metro area. So only kept mention for
some light fog at KSUS in river valley. Otherwise, south winds to
persist. Still some concern for LLWS as upper level jet ramps up a
bit, so kept mention in taf with it diminishing by 14z Saturday.



Issued at 1253 AM CST Fri Jan 20 2017

January 21st Record High Information

St. Louis, Missouri  STL  75  (1986)
Columbia, Missouri   COU  73  (1957)
Quincy, Illinois     UIN  69  (1957)




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