Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 201149

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
649 AM CDT Mon Mar 20 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 333 AM CDT Mon Mar 20 2017

Low pressure over southeast Nebraska will move east this morning
and then southeast this afternoon and evening.  The warm front ahead
of the low will pass over the area this morning and temperatures
should shoot up quickly into the low and mid 70s...topping out in
the low to mid 80s across parts of central and eastern Missouri this
afternoon.  The model consensus has the cold front trailing the low
entering northern portions of the CWFA by early afternoon.  Cold
front will progress down to near I-44/I-64 by 00Z.  Current thinking
on precip is that most if not all of the area will stay dry today.
Model soundings show a pretty substantial amount of CINH in place.
However, RAP shows some low level moisture convergence developing
ahead of the 850mb front late this morning/early this afternoon
south of I-70 and some corresponding light QPF.  Most of the
convection allowing models show some isolated/widely scattered
convection breaking out in these areas too, so have kept some slight
chance PoPs across the eastern Ozarks into southwest Illinois.

The cold front continues south tonight and stalls over southern
Missouri/northern Arkansas as another wave develops over the southern
Plains.  Most models develop some precipitation across southern
Missouri and Illinois tonight as the low level jet streams out of
southeast Texas and Oklahoma into the baroclinic zone over the
Missouri/Arkansas border.  Not sure what the coverage and intensity
of the precip will be at this time, so stuck with chance and slight
chance PoPs.  MOS lows behind the cold front from the low 40s in
northeast Missouri/west central Illinois to the low 50s in southeast
Missouri look reasonable.


.LONG TERM...  (Tuesday through Sunday)
Issued at 333 AM CDT Mon Mar 20 2017

Still looks like a pretty active week weatherwise with several
chances of showers and thunderstorms.

Showers still look likely on Tuesday and Tuesday night with a cold
front to the south of the area. GFS and ECMWF are still showing
sustained low level moisture convergence under mid-level ascent in
west northwesterly flow aloft. It still appears that there will be
some break in the precipitation Wednesday into Wednesday night as an
upper ridge and a surface ridge move in tandem across the area.  The
chance of precipitation will increase again by late Wednesday night
into Thursday morning as a broad swath of moisture return occurs on
the back side of the low level ridge.

GFS has come into better agreement with the ECMWF by late week into
the weekend with a deeper, slower solution of the upper low that
will move from central high Plains into Middle Mississippi Valley.
The warm front will move north of the area by Thursday afternoon and
Thursday night leaving most of the area dry.   Have likely and
categorical PoPs by late Friday into Saturday as there will be
strong moisture transport from the Gulf ahead of the upper low.
Upper low will be slow to move across the area, so it will keep
chance PoPs in the forecast through next weekend.

GEFS MOS mean guidance show temperatures staying close to normal
Tuesday into Thursday before climbing above normal on Friday and
Saturday once the area lies in the warm sector. Temperatures will
fall back closer to normal on Sunday behind the passage of a cold



.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 626 AM CDT Mon Mar 20 2017

Isolated showers are developing and dissipating along a line from
KSPI to KUUV. The line is moving southeast at around 20kts. Expect
this intermittent activity to continue through 13-14Z. Ceilings
associated with the precip are VFR...but isolated visibility
could briefly be reduced to MVFR or below. Remainder of the area
is expected to remain VFR through at least the afternoon into the
evening. A cold front will move from northwest to southeast
across the area today. Isolated to widely scattered thunderstorms
are possible ahead of the front...primarily south of the I-70
corridor this afternoon and evening. Wind south of the front will
be from the west-southwest. Wind will turn to the north and then
the northeast after the front moves through the region. Model
guidance is indicating that MVFR ceilings and intermittent rain
are possible late tonight behind the cold front...primarily along
and south of the I-70 corridor.


An isolated shower may affect Lambert before 13Z this morning.
Little impact is expected...though if a stronger shower develops
the visibility could briefly drop to MVFR...tho this is very
unlikely. Remainder of the day into the evening is expected to be
VFR. Wind will flirt with a direct crosswind at 210 degrees for a
brief period this morning before turning more west-southwesterly.
A cold front will pass through the terminal between 21-00Z which
will turn the wind to the north, and then northeast in the
evening. Model guidance is indicating that MVFR ceilings and are
possible late tonight.





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