Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 190454
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1054 PM CST Wed Jan 18 2017

.UPDATE...
Issued at 931 PM CST Wed Jan 18 2017

A modest south-southwesterly low level jet will bring increasing
low level moisture and cloudiness northward into our forecast area
late tonight, well ahead of the slow moving upper level low over
the central Plains. The radar has begun to detect very low
reflectivities developing from just south of JEF to near VIH. The
model guidance has mainly light rain or showers late tonight
across southeast into central MO, mainly south of Interstate 70.
With increasing low level cloud cover and southeasterly surface
winds the lows tonight will be slightly warmer than the previous
night and about 15 to 20 degrees above normal.

GKS

&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 325 PM CST Wed Jan 18 2017

Forecast is still on track that showers and a few thunderstorms will
move into the area late tonight and tomorrow.

Low clouds broke up across the area today only to be replaced by mid
and high clouds that are streaming northward ahead of a dual upper
low currently over western Kansas and New Mexico.  This moisture
stream will continue to cause clouds to lower and thicken across the
area through the evening hours.  The chance for showers will
increase by late this evening over southeast Missouri as moisture
convergence increases on the nose of a low level jet underneath
increasing mid level ascent ahead of the upper low.  The chance of
for showers will spread northward and increase across the area
overnight into Thursday morning as the upper low moves eastward.
The greatest chance for showers and highest rainfall totals will
be across southeast Missouri into southern Illinois where the
strongest low level forcing and precipitable moisture will be.
There will still some potential for thunderstorms tomorrow as
lapse rates steepen with the upper low. The chance of rain will
begin to taper off from west to east late in the day as the
forcing lifts eastward.

Temperatures will show little diurnal swing the next 24 hours
because of the clouds and the rain.  They are a combination of
compromise MOS values and SREF 2 meter temperatures.

Britt

.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 325 PM CST Wed Jan 18 2017

Amplified weather pattern will remain over the CONUS from Thursday
night through the end of the forecast period on Wednesday. The main
feature of this pattern will be the longwave trof now off the west
coast of North America.  This trof will dig across the western
states remaining in place through early next week.  Persistent south
to southwest flow over the region will keep temperatures well above
normal.  In fact, the warmest day in the upcoming stretch looks to
be Saturday with highs in the low to mid 60s which is pushing 30
degrees above normal for mid to late January.

Several shortwaves will rotate around the base of the persistent
western trof and eject northeast across the Plains.  These waves
combined with moisture convergence on the low level jet will keep a
persistent chance of showers to the area at least through Sunday
night and into Monday morning.  The pattern begins to shift Monday
night and Tuesday as the longwave trof finally moves east into the
Great Plains.  Current indications are that Tuesday will be dry but
the chance of showers will return Tuesday night as ridging ahead of
the longwave shifts east and southwest flow returns.

Carney

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1038 PM CST Wed Jan 18 2017

Surface ridge centered over the OH Valley region will continue to
shift eastward. Mid-high level cloudiness will continue to spread
through our area ahead of a slow moving upper level low over the
central Plains. Low level moisture and cloudiness will advect
northward into the taf sites late tonight and Thursday morning
with the cloud ceiling eventually dropping into the IFR catagory.
Visibilities will also lower due to a combination of fog and light
rain or showers moving into COU and the St Louis metro area late
tonight/Thursday morning and eventually into UIN. A weak southeast
surface wind will become more easterly Thursday afternoon.

SPECIFICS FOR KSTL: Surface ridge centered over the OH Valley
region will continue to shift eastward. Mid-high level cloudiness
will continue to spread through our area ahead of a slow moving
upper level low over the central Plains. Low level moisture and
cloudiness will advect northward into the STL area late tonight
and Thursday morning with the cloud ceiling eventually dropping
into the IFR catagory. Visibilities will also lower due to a
combination of fog and light rain or showers moving into STL late
tonight/Thursday morning. The showers will eventually shift east
of the STL area by late Thursday night, but the low level stratus
clouds and fog will remain. A weak southeast surface wind will
become more easterly Thursday afternoon.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     40  50  44  58 /  40  70  50  20
Quincy          35  44  39  52 /  10  60  60  20
Columbia        39  48  42  57 /  40  40  30  20
Jefferson City  41  49  42  58 /  40  40  30  20
Salem           39  51  46  57 /  30  70  70  20
Farmington      41  51  44  58 /  60  70  40  20

&&

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

$$

WFO LSX



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