318 
FXUS63 KLSX 102343
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
643 PM CDT Wed Oct 10 2018

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 337 PM CDT Wed Oct 10 2018

The cold front was located from western IL into far southeast MO
late this afternoon, and moving east at a decent clip. Instability
is diminishing along and ahead of the front, and spotty showers
will remain possible with the front during the remainder of the
afternoon as it progresses through southwest/south central IL. 
The the main story tonight will be chilly temperatures and slowly 
decreasing cloud cover. West northwest winds will diminish by 
early evening but will continue to usher much colder air into the 
area. Tonight will be the coldest thus far this fall. I am a bit 
pessimistic on the clouds clearing given the upstream extent and 
have slowed the trend from the previous forecast.

Weak CAA will persist in the morning and I think any remaining
clouds will decrease and/or we will see just some scattered
diurnal cu develop. Highs will be significantly colder than today
and all but far southeast MO and southwest IL will remain in the
50s.

Glass

.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 337 PM CDT Wed Oct 10 2018

High pressure will dominate the area Thursday night and the main
question for this period is the potential for any frost. The
evening and first part of the overnight period will be relatively
void of clouds. With light winds we should temperatures fall
rather quick and I have mentioned some frost across northern
portions of the CWA, roughly north of I-70. Clouds will begin to
overspread the area before daybreak on Friday ahead of the next
system. An upper trof will move southeastward from the northern
Plains into the mid-upper MS Valley on Friday. Large scale 
forcing associated with the trof along with low level WAA and
low-mid level frontogenetic forcing will result in a large rain
area of rain overspreading across the region from the west. The
combination of clouds and diabatic cooling will make for a cold
day/rain and well below average temperatures, especially across
northeast MO and west central IL. The rain shield should exit to
the east of the area by late evening in association with the
progression of the upper trof and forcing. Temperatures will fall
into the 30s overnight and surface winds will be light. Normally
this would suggest frost potential, however the wet ground from
the rain and likelihood of lingering clouds are negative factors
and will not mention any frost at this time.

Another upper trof moves into the Plains late Sunday and advances
into the Mid Mississippi Valley in the Monday-Monday night time 
frame. The ECMWF and GFS differ a bit handling this trof and the 
associated rain shield which is largely driven by frontogenetic 
forcing. At this time we have favored the wetter ECMWF solution 
which spreads rain across the southern 2/3rds of the area Sunday 
into Sunday night.

Little or no precipitation is expected Tuesday into Wednesday with
temperatures at or below average.

Glass

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 621 PM CDT Wed Oct 10 2018

Main questions tonight will be how long MVFR clouds linger as well
as how long gusts remain into the evening. Believe wind gusts will
diminish over the next couple of hours, however, there is some
indication some gusts, especially at KUIN/KCOU, will linger thru
the evening hours. Expect closed cell CU to persist thru much of 
the night and becoming scattered shortly after sunrise. The latest
hourly updating model guidance suggests that cloud cover shud 
remain scattered. However, given upstream cloud cover, this seems 
to be an optimistic forecast. Still, believe there will be
slightly more breaks in clouds compared to today, resulting in
higher bases. Expect nwly winds on Thurs with gusts to around 18 
kts. 

SPECIFICS FOR KSTL: Expect MVFR cigs to move into the region and
impact the terminal around 01z. There is some question regarding
if/when these cigs will break up, but believe MVFR cigs will
persist thru tonight and break up around sunrise Thurs. There is
some indication that going forecast does not have enuf cloud cover
for Thurs. Will hold off with any major changes for now, but
believe that bases will be low VFR during the afternoon hours. 

Tilly

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX