Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 210542
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1142 PM CST Fri Jan 20 2017

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 316 PM CST Fri Jan 20 2017

Main issue will be fog potential tonight.

Clearing line continues to slowly advance newd this afternoon. With
nrn portions of the CWA clearing late this evening or after
Midnight, expect at least some light fog to develop overnight.
However, if mixing persists longer, fog may not develop. Regardless,
it does not currently appear that visbys will drop into the dense
fog category.

Focus then turns to temps on Sat. Have conflicting guidance with the
GFS suggesting warmer temps with deeper mixing while the NAM limits
mixing to around 1200 ft. Upstream obs show temps have topped out in
the upper 60s with a few 70s. Do expect some clouds, perhaps
becoming broken, during the day. While these are expected to be mid
and high clouds, this shud limit heating a bit. Going forecast
appeared close and made only minor modifications.

A s/w will be passing thru the region ahead of the approaching
system during the afternoon on Sat. There is some difference among
mdl guidance, but believe there will be a lack of moisture to expect
precip.

Tilly

.LONG TERM...  (Saturday Night through Next Friday)
Issued at 316 PM CST Fri Jan 20 2017

A powerful storm system that will come onshore to southern
California this evening will enter a pattern of a longwave TROF that
dominates much of the western CONUS.  This storm is then expected to
track across the southern CONUS and pass to our south on Saturday
night and Sunday.  Normally this time of year, a track such as this
would raise eyebrows on potential for a significant winter storm
somewhere in our CWA, but there is no cold air anywhere to be found
or tap with this system.  The EC is showing a bit better northward
extent to its pcpn shield than the other models, but either way, the
pcpn-types should be all rain.

After a brief interlude of a weak RIDGE thru our region late Monday
into early Tuesday, another strong Pacific storm system will
approach late Tuesday.  The brunt of the lift with this system will
pass to our north Tuesday night, but several models are showing
additional and weaker upper level disturbances sliding down into our
region from the resultant northwest flow aloft for much of the
period from Wednesday into Friday.  However, the column gets
progressively drier and confidence decreases on any one event with
time, and so have tapered off PoPs as a result.  Pcpn-types will be
more questionable late Tuesday into Wednesday, especially in
northern MO and central IL, and have a rain-snow mix at times for
these areas.

Temperatures are expected to remain above average until the middle
of next week, with a more favorable pattern for cold air attempting
to setup afterwards.

TES
&&

.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.

SPECIFICS FOR KSTL:
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.

Byrd
&&

.CLIMATE...
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)


&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     49  68  46  53 /   5   5  30  70
Quincy          44  60  39  47 /  10   5  10  30
Columbia        45  63  42  48 /   5   5  20  50
Jefferson City  44  65  42  50 /   5   5  20  50
Salem           50  66  48  57 /   5   5  30  60
Farmington      50  65  47  54 /   5  10  40  70

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$
WFO LSX


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