Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 200202
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
802 PM CST Thu Jan 19 2017
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.
.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.
.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.
.AVIATION... (For the 00z TAFs through 00z Friday Evening)
Issued at 542 PM CST Thu Jan 19 2017
Main issue tonight and Friday morning will be stratus cloud deck
below 500 feet in height along with low visibilities in fog.
Visibilities will lower to one quarter to one half mile this
evening in areas which are not already this low. Scattered rain
and showers, mainly light across central and southeast MO may
impact UIN and the St Louis metro area later this evening. Patchy
drizzle can also be expected through the night. East-southeast
surface wind will become light later this evening. Will see
gradual improvement of ceilings and visibilities late Friday
morning and afternoon to MVFR conditions with a southeast surface
wind increasing to around 7-8 kts.
SPECIFICS FOR KSTL: Main issue tonight and Friday morning will
be stratus cloud deck below 500 feet in height along with low
visibilities in fog. Visibilities will lower to one quarter mile
later this evening. Scattered rain and showers, mainly light
across central and southeast MO may impact the STL area later
this evening. Patchy drizzle can also be expected through the
night. East-southeast surface wind will become light later this
evening. Will see gradual improvement of ceilings and visibilities
late Friday morning and afternoon to MVFR conditions with a
southeast surface wind increasing to around 7-8 kts.
.PRELIMINARY POINT TEMPS/POPS...
Saint Louis 45 57 48 64 / 70 10 5 10
Quincy 39 52 45 59 / 30 20 10 5
Columbia 42 58 45 62 / 30 10 0 5
Jefferson City 44 59 45 64 / 30 10 0 5
Salem 47 56 49 63 / 80 20 10 20
Farmington 45 57 48 64 / 80 20 5 20
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.