Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 270853
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
353 AM CDT MON JUN 27 2016

.SHORT TERM...  (Through Late This Afternoon)
Issued at 301 AM CDT Mon Jun 27 2016

The initial boundary appears to have pushed south of the CWA however
it is rather ill-defined and the surface winds across the area are
quite weak. The combo of the light/calm winds and precipitation
from yesterday has resulted in low T/Td spreads and the development
of dense fog across a good portion of central and northeast MO
into far west central IL. Conditions are not expected to change
much through sunrise, and if anything the loss of higher clouds
will help the fog potential. I have issued a dense fog advisory
with both the operational and experimental HRRR showing good
support keeping this area socked in through 12z or so, and then
the fog dissipating between 14-15z.

Only some spotty showers were ongoing early this morning aross
southwest IL and parts of southern MO. These were occuring in
advance of a weak short wave extending from south central MO into
western AR. Southern MO and southern IL will continue to have a
threat of scattered precipitation this morning as this short wave
moves to the east-southeast while clouds will gradually thin as
well and shunt souteastward. While dew points are rather high at
this time, all indications are they will decrease later this
morning as the wind increases and mixing increases. A secondary
cold front will then drop into northern MO and central IL this
afternoon eventually bringing cooler and drier air. High temps
will once again be seasonably hot but humidity this afternoon
should be markedly lower.

Glass

.LONG TERM...  (Tonight through Sunday)
Issued at 301 AM CDT Mon Jun 27 2016

The cold front will continue to move south across the remainder of
the CWA tonight in response to an upper trof digging into the
Great Lakes and Ohio Valley. Cooler and drier air will continue to
spread into the area as surface high pressure builds into the area in
the wake of the cold front. Noteworthy is the GFS wants to generate
some light precipitation behind the front tonight, apparently in
response to low level frontogenetic forcing. I have chosen to disregard
this solution at this time. High pressure will then continue to
build southward into the Mid MS Valley Tuesday and Tuesday night.
There are varying signals that a northwest flow disturbance and
low level frontogenetic forcing may generate some showers and
thunderstorms across parts of eastern KS/western MO on Tuesday,
which may clip parts of central and southeast MO. I have continued
with a slight chance POP as a result.

Otherwise below average temperatures will be the story and we
continue to watch a series of northwest flow short waves Wednesday
through Friday and monitor potential impacts. The wave on
Wednesday appears well to the west, while another on Thursday
should mainly bring showers and storms to eastern KS and western
MO. Central MO could see showers and storms from the eastern
extension of any MCS.

The greatest threat of precipitation across the CWA will unfold
Friday into Saturday night a pronlonged series of weak low-
amplitude short waves traverse the area. The first of these will
bring a cold front passage and that front eventually becomes
quasi-stationary from southern KS across far southern MO by
Friday evening. The flow aloft at that time will be more west-
northwesterly and a pronounced overrunning/WAA pattern appears to
be setting up from KS across southern MO and southern IL for
multiple MCS events Friday night thru Saturday night.

Glass

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1123 PM CDT Sun Jun 26 2016

Showers and thunderstorms have moved south of taf sites. Some
lingering isolated rain/sprinkles at times for next couple of
hours. Otherwise, mid and high clouds with light winds. With
front stalled out just south of forecast area and plenty of low
level moisture, patchy dense fog has developed over portions of
the area as of 04z. So added fog mention to majority of tafs.
Lowest cigs/vsbys will be over KUIN and KCOU, so expect ifr/lifr
conditions at times through daybreak. For KSUS and KCPS, just have
mvfr vsbys between 08z and 12z Monday.

Specifics for KSTL:
Showers and thunderstorms have moved south of metro area. Some
lingering isolated rain/sprinkles at times for next couple of
hours. Otherwise, mid and high clouds with light winds. With
front stalled out just south of forecast area and plenty of low
level moisture, patchy dense fog has developed over portions of
the area as of 04z. So added fog mention to KSUS and KCPS with
mvfr vsbys between 08z and 12z Monday.

Byrd

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Dense Fog Advisory until 10 AM CDT this morning for Audrain MO-
     Boone MO-Callaway MO-Cole MO-Gasconade MO-Knox MO-Lewis MO-
     Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike
     MO-Ralls MO-Shelby MO.

IL...Dense Fog Advisory until 10 AM CDT this morning for Adams IL-
     Brown IL-Pike IL.

&&

$$

WFO LSX


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