Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 230430
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1130 PM CDT Sun Oct 22 2017

.UPDATE...
Issued at 909 PM CDT Sun Oct 22 2017

Rain continues this evening across east central and southeast MO
and southwest IL due to an upper level low centered over
northwestern AR. Most of the rain was from the St Louis metro area
south and east. The upper level low will slowly deepen as it
moves eastward into the MO bootheel by 12Z Monday. By early
morning the rain may be more patchy or scattered and generally
lighter in intensity, but may still be across parts of southeast
MO and southwest IL. The sky should clear out from west to east
across northeast and central MO late tonight. This is where the
coldest temperatures can be expected. Although lows will be much
colder tonight, they will be close to seasonal normals for late
October.

GKS

&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 319 PM CDT Sun Oct 22 2017

System taking its time lifting northeast out of region, so cold
front has yet to move through our far eastern counties as of 19z,
winds at Salem/Centralia are still from the south. In the meantime,
shower coverage has greatly diminished with patchy drizzle
developing.

As main upper level shortwave lifts northeast through region late
this afternoon/tonight, will see increasing coverage of showers once
again, mainly over eastern portions of forecast area. In the
meantime, cloudy and drizzly conditions to prevail. Clearing line,
currently over far western MO, will gradually shift east tonight,
with clouds scattering out over central/northeast MO late this
evening, reaching the STL metro area by 12z Monday. With decent low
level moisture in place due to prior precipitation and winds
becoming light and variable, could see some patchy fog develop over
central/northeast MO, west central IL so added mention to these
areas between 06z and 13z Monday.

On Monday, upper level low will have yet to exit eastern portions of
region, so will have lingering showers over portions of southwestern
IL through out the day, while rest of forecast area to see some sun
and dry conditions.

Colder air is filtering in, so will have lows in the low 40s to low
50s tonight. With partly to mostly sunny skies on Monday, highs will
rebound a bit, into the low 60s to low 70s.

Byrd

.LONG TERM...  (Monday Night through Next Sunday)
Issued at 319 PM CDT Sun Oct 22 2017

Models are in good agreement thru much of the forecast period.
Overall, expect the period to be largely dry although, there is
uncertainty for Fri and beyond. Somewhat large temperature swings
are expected until Fri and beyond with much cooler temps are
expected to remain in place thru the end of the period.

Large low over the Great Lakes region on Tues will keep cold air in
place. Cyclonic flow shud keep stratocu in place and help keep temps
cooler. Also kept low PoPs for the afternoon hours as a s/w drops
south into the region.

Temps rise quickly on Wed and Thurs as a clipper passes just north
of the CWA and ahead of another approaching low system. Thurs shud
still be the warmest day of the week and the going forecast may
still be a bit on the cool side. However, some uncertainty remains
regarding the timing of the warmer 850mb temps and the approaching
cdfnt.

Confidence continues to increase in a period of below seasonal
average temps late next week and into the weekend. The 12z guidance
is in much better agreement, however, the ECMWF still has the upper
trof hanging up further west compared to the GFS/GEM solns. Have
trended this period much drier, but did keep low PoPs going to
attempt to account for precip associated with the cdfnt as well as
possible showers embedded within stratocu as potential s/w drops
thru the area.

Have also trended colder thru this period as well and therefore, can
not rule out possible snow showers, but confidence is rather low at
this point. Regardless, pattern looks cold and confidence in a hard
freeze is increasing. The going forecast is probably too warm at
this point, but differences in model solns, decided to not trend too
cold yet.


Tilly

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1116 PM CDT Sun Oct 22 2017

Although the cold front has shifted well east-southeast of the
taf sites this evening with weak surface ridging into northern
and western MO, an upper level disturbance centered over
northwestern AR will continue to bring light rain to the St Louis
metro area into the overnight hours. IFR/MVFR ceilings were also
across the St Louis metro area, around 800 to 1400 feet. The cigs
should improve into the VFR catagory by 10-14Z across the St
Louis metro area. The rain should become lighter and more spotty,
finally coming to an end by late Monday morning as the upper
level disturbance shifts east-southeast of the area. The VFR
cloud cover will clear out of UIN and COU late tonight as the
clearing line over western MO continues to shift eastward. Could
not rule out patchy light fog in UIN and COU late tonight and
early Monday morning, although lowering surface dew points will
keep any visibilities from dropping very low. A dry cold front
will move southeastward through the taf sites Monday afternoon.
Relatively strong and gusty northwesterly surface winds can be
expected after fropa due to a tightening surface pressure gradient
as a strong surface ridge builds southeastward into the region
behind the cold front.

SPECIFICS FOR KSTL: Although the cold front has shifted well
east-southeast of the STL area this evening with weak surface
ridging into northern and western MO, an upper level disturbance
centered over northwestern AR will continue to bring light rain to
the STL area into the overnight hours. IFR/MVFR ceilings were
also across the St Louis metro area, around 800 to 1400 feet. The
cigs should improve into the VFR catagory by 09-13Z at STL. The
rain should become lighter and more spotty, finally coming to an
end by late Monday morning as the upper level disturbance shifts
east-southeast of the area.  A dry cold front will move
southeastward through the STL area Monday afternoon. Relatively
strong and gusty northwesterly surface winds can be expected after
fropa due to a tightening surface pressure gradient as a strong
surface ridge builds southeastward into the region behind the cold
front.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     50  69  47  54 /  80  10   5  20
Quincy          44  65  42  50 /  10   5   5  20
Columbia        43  67  43  53 /  10   5   0   5
Jefferson City  42  68  44  54 /  10   5   0   5
Salem           51  64  45  54 / 100  40  10  20
Farmington      47  70  44  56 / 100  10   0   5

&&

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

$$

WFO LSX


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