Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 251803
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1203 PM 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 18z TAFs through 18z Thursday Afternoon)
Issued at 1159 AM CST Wed Nov 25 2015
A few sprinkles may still affect the St. Louis metro TAF sites early
in the TAF period, otherwise expect most of the afternoon to be dry.
Expect clouds to move back into the area this afternoon and ceilings
to be either high MVFR or low VFR during the period. There will be
some potential for increasing rain chances, particularly at KUIN and
KCOU on Thursday morning. A low level jet will develop this evening
and have added LLWS this at all of the terminals.
Specifics for KSTL: May still be a few sprinkles early this afternoon
at the terminal along with the possibility of high MVFR ceilings, but
currently think that ceilings will stay in the low VFR range. A low
level jet will develop over the area by early this evening, so have
added LLWS this evening. There will be the potential for scattered
rain showers to develop over the area by late tonight or during the
day tomorrow, but have kept them out of the forecast for now as I do
not have enough confidence on timing. There also is the possibility
of high MVFR ceilings developing at the terminal at times tonight
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-