Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 251651

1051 AM CST WED NOV 25 2015

Issued at 1049 AM CST Wed Nov 25 2015

Isolated light showers have develop over eastern Missouri and
southwestern Illinois late this morning ahead of a shortwave
trough that is moving across the region. Have added isolated
forecast over the central and eastern counties through early
afternoon ahead of the trough until it exits the area.

Central and northeastern Missouri is currently mostly sunny, but
more clouds should push into the area this afternoon as 12Z upper
air analysis showed a significant low level moisture transport
into Missouri. Adjusted highs to be warmest were the sun is
currently out, with cooler readings over southeast Missouri.



.SHORT TERM:  (Through Late This Afternoon)
Issued at 358 AM CST Wed Nov 25 2015

WAA is in full force today with SW upper flow coupled with decent
sthrly sfc flow. Players for the end of the week will come into
better focus today. Sthrly winds are expected to pick up today in
response to tightening pressure gradient between sfc ridge mvng off
the NE Coast and a dvlpng sthrn high plains low. Lee side
cyclogenesis will continue today on the tail end of the strengthening
front that is fcst to move through the region tomorrow and Friday.

Return flow stratus will continue to affect the wrn/nthrn CWA across
cntrl/NE MO and w cntrl IL...though the ern edge of the clouds is a
bit iffy. Moisture on the ern flank of the higher RHs is thinner
than farther west. Think the eventual edge of the clouds will thin
thru the day before the stratus moves back in tonight.

Expect the day to be dry although I can`t rule out some light rain
late this aftn across the NW FA. WAA precip seems to dvlp ahead of
schedule...esp in strong WAA regimes like this one. Held off on
drizzle due to the low level moisture profile...not expected CIGs
below 2kft...drizzle is more assoc with IFR CIGs.

Due to the strength of the WAA...clouds do not appear to be a
significant limiting factor in temps today. Still expect highs in
the upper 50s to lower 60s despite widespread stratus across
wrn/nthrn parts of the area.


.LONG TERM:  (Tonight through Tuesday)
Issued at 358 AM CST Wed Nov 25 2015

(Tonight through Friday night)

Focus continues to be precip chances into the weekend and now,
rainfall amounts. Given the rainfall amounts, have decided to issue
a Flood Watch for the srn half of the CWA.

Not many changes from the prev forecast. Main changes were to warm
temps slightly again, reducing diurnal temp swing given the amount
of cloud cover and strong sly winds ahead of the fnt.

Changes to PoPs have been minor, however, despite the slower fnt
timing. This is to hopefully capture the precip chances with the
very strong WAA ahead of the fnt. Overall, mdls are in good
agreement and confidence in a heavy rainfall event are increasing
across the srn half of the CWA. Have decided to issue a Flood Watch
for areas where 2.00 inches of rainfall are expected thru Fri night.
The watch may need to be expanded in area and possibly thru Sat.
However, inconsistencies among mdls and from one cycle to the next,
leads to lower confidence in precip placement for this weekend. Will
wait for better mdl agreement to extend the watch if needed.

(Saturday through Tuesday)

As mentioned above, mdl solns vary regarding mass fields for the
system this weekend and into next week. Overall trends have been to
push the fnt and sfc wave further south. The 25/00z GFS places the
sfc wave on Sun in nearly the same place the 24/00z ECMWF did. This
seems to be a common trend, but is always difficult to determine if
the trend continues. Still, confidence in precip chances across srn
are increasing and have increased PoPs for those times when and
where mdls are in agreement.

Mdl differences increase thru the extd and have kept low PoPs into
Mon night due to the uncertainty. Due to the uncertainty and mdl
solns, have continued a ECMWF/GFS compromise for temps thru the
extd. The GEM continues to be an outlier and this soln has been
ignored for now.



.AVIATION:  (For the 12z TAFs through 12z Thursday Morning)
Issued at 536 AM CST Wed Nov 25 2015

VFR fcst thru the prd...though all sites will continue to deal
with LLWS for a few more hours this mrng. The LLWS threat ends as
the bndry layer begins to mix later this mrng and gusts pick up.
The LLWS threat may return tonight. VFR stratus will affect
cntrl/NE MO into w cntrl IL thru the fcst prd. There is some
question as to the ern extent of the lower cloud deck by this
aftn...but since it is already overtaking the STL metro TAF
sites...think they will stay at least BKN most of the day.

Specifics for KSTL:

VFR fcst with LLWS this mrng and possibly again tonight. VFR
stratus is currently encroaching upon the terminal and should
remain in place thru the remainder of the fcst period. CIGs may
begin to build down towards MVFR territory towards the end of the



MO...Flood Watch from Thursday evening through late Friday night FOR
     Boone MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-
     Gasconade MO-Iron MO-Jefferson MO-Madison MO-Moniteau MO-
     Montgomery MO-Osage MO-Reynolds MO-St. Charles MO-St.
     Francois MO-St. Louis City MO-St. Louis MO-Ste. Genevieve
     MO-Warren MO-Washington MO.

IL...Flood Watch from Thursday evening through late Friday night FOR
     Clinton IL-Madison IL-Monroe IL-Randolph IL-St. Clair IL-
     Washington IL.



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