Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 200429
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1029 PM CST Thu Jan 19 2017

.UPDATE...
Issued at 749 PM CST Thu Jan 19 2017

Area of showers and embedded thunderstorms moving slowly northward
through parts of southeast MO and southwest IL. This precipitation
will impact the St Louis metro area later this evening, especially
the eastern half of the metro area. The visibilities may improve
as this rain moves, but should drop back down later tonight.
Otherwise and elsewhere fog will plague the forecast area with
visibilities dropping down to one quarter of a mile or less along
with patchy drizzle. Temperatures will remain nearly steady and be
quite mild for late January. Low temperatures tonight will be
about 20 degrees above normal.

GKS

&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 404 PM CST Thu Jan 19 2017

Main issue tonight is the fog. Saturated atmosphere, light wind
overnight is a good situation for dense fog to develop. In fact
there are visibilities already that are near 1/4 mile. Improvement
should take place by mid-morning at the second is a series of upper
low pressure areas lifts north of the area. Weak high pressure moves
in during the afternoon as the surface low moves to the Great Lakes.
Still plenty of clouds around though so don`t expect the sun to make
much of an appearance. Not much temperature change tonight. Might
be too optimistic on highs for Friday.

JPK

.LONG TERM...  (Friday Night through Next Thursday)
Issued at 404 PM CST Thu Jan 19 2017

Highly amplified weather pattern over the CONUS will persist into
next week.  The main feature continues to be the longwave trof off
the West Coast which will dig in over the Four Corners region by
early next week.  Three primary shortwaves will rotate around the
base of the longwave and eject northeast from the Great Plains
across the Midwest through next Thursday.  The first will move from
Kansas up into Iowa and Minnesota Friday night and Saturday.  Looks
like the best forcing will slide northwest of the area and current
guidance has little or no precip falling Friday night and Saturday.
Did keep some chance to slight chance PoPs going Saturday afternoon
and Saturday night though since guidance is showing low level
moisture convergence on a 30-40kt low level jet.  The second
shortwave is now forecast to move further south than in previous
runs, and cross the Mississippi River early Sunday afternoon over
the Arkansas/Mississippi/Louisiana border. The precipitation
associated with this wave looks to mainly stay south of the
area...though there is a chance for some showers mainly along and
southeast of the I-44/I-55 corridors through Sunday evening.
Amplified pattern shifts east as an upper level ridge moves over the
area early next week...and the third shortwave ejects into the
Midwest late Tuesday night and Wednesday.  This looks like much
better chance for rain across much of the area...at least ahead of
the surface system on Tuesday afternoon and Tuesday night.

Temperatures look to remain well above normal through the medium
range with no real cold air outbreaks on the horizon.  Even sub
freezing temperatures will be hard to come by, with lows primarily
in the mid 30s to mid 40s and highs creeping up into the 50s many
days, and even 60s on Saturday.

Carney

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1017 PM CST Thu Jan 19 2017

Main issue late tonight and Friday morning will be stratus cloud
deck below 500 feet in height along with low visibilities in fog.
An area of showers and a few thunderstorms moving through the St
Louis metro area this evening have caused some improvement in the
visibilities and ceiling heights, but this should be short lived
with visibilities expected to drop back down to one quarter of a
mile overnight. Patchy drizzle can also be expected for the rest
of the night. Will see gradual improvement of ceilings and
visibilities late Friday morning and afternoon to MVFR conditions
with a southeast surface wind increasing to around 7-9 kts.

SPECIFICS FOR KSTL: Main issue late tonight and Friday morning
will be stratus cloud deck below 500 feet in height along with
low visibilities in fog. An area of showers and a few thunderstorms
moving through the St Louis metro area this evening have caused
some improvement in the visibilities and ceiling heights, but this
should be short lived with visibilities expected to drop back down
to one quarter of a mile overnight. Patchy drizzle can also be
expected for the rest of the night. Will see gradual improvement
of ceilings and visibilities late Friday morning and afternoon to
MVFR conditions with a southeast surface wind increasing to around
7-9 kts.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     45  57  48  64 /  90  10   5  10
Quincy          39  52  45  59 /  30  20  10   5
Columbia        42  58  45  62 /  20  10   0   5
Jefferson City  44  59  45  64 /  20  10   0   5
Salem           47  56  49  63 /  90  20  10  20
Farmington      45  57  48  64 /  90  20   5  20

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Dense Fog Advisory until 8 AM CST Friday for Audrain MO-Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln MO-Madison MO-
     Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike
     MO-Ralls MO-Reynolds MO-Saint Charles MO-Saint Francois MO-
     Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-
     Shelby MO-Warren MO-Washington MO.

IL...Dense Fog Advisory until 8 AM CST Friday for Adams IL-Bond IL-
     Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey
     IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Pike IL-Randolph IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX



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