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FXUS63 KLSX 210448

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1148 PM CDT Fri Sep 20 2019

.SHORT TERM...  (Through Late Saturday Night)
Issued at 253 PM CDT Fri Sep 20 2019

No changes to the Flash Flood Watch. 

Moisture continues to surge northward into the region, evident in
TSRA coverage over southern portions of the CWA. Storms should
diminish with sunset, however, expect storms to linger a little
longer than over the past couple of days. 

The focus of precip should shift to western, then northern, 
portions of the CWA as the LLJ increases. That said, with the vort
max over southern MO into AR lifting into the region, going
forecast may not have high enough PoPs far enough southeast.
Models are also suggesting a band of showers lifting eastward
through the central portions of the CWA around and just after
sunrise. Some of the later cycles of the RAP have shifted this a
little further north. As such, confidence remains on the lower end
for timing and placement. 

Still expect precip to gradually diminish through the morning
hours. After a lull in activity through much of the afternoon,
expect precip coverage to increase across northern portions of the
CWA during the late afternoon and persist through the overnight


.LONG TERM...  (Sunday through Next Friday)
Issued at 253 PM CDT Fri Sep 20 2019

Main focus continues early in the period. A confluent upper trof
approaches the region on Sun with the surface cold front reaching
northern portions of the CWA mid to late Sun morning. Moisture
advection ahead of this front continues with PWs of 2+ inches.
With the LLJ parallel to the front, training storms will be
possible. These factors in addition to high freezing level and 
the high PWs, a threat of flash flooding exists for mainly the 
northern third or so of the CWA. However, will keep the watch as 
is due to continued uncertainty. With the available CAPE and deep
layer shear ahead of the front on Sun, will need to continue to
monitor a severe threat. 

The cold front is expected to push south through the area Sun
night with rain coming to an end. After a dry Mon and most of
Tues, the chance for rain increases again mid to late week. With
differences among model solns, have kept PoPs low for now. 



.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1136 PM CDT Fri Sep 20 2019

Isolated to scattered showers and storms are expected to develop
in central and NE MO early this morning, pushing east through the
morning hours. There is some uncertainty just how far south and 
east these storms will reach, with UIN being the only terminal 
where precip is likely this morning. The moisture that will help 
develop these storms will also result in MVFR cigs in these 
areas, perhaps falling to low end MVFR for areas directly impacted
by any storms. 

Thinking storm activity will diminish somewhat in the afternoon,
though like the last few days, isolated storms will be possible.
Also like the last few days, it's difficult to tell if any 
terminals, will be directly impacted by these afternoon storms.
Moisture is a bit richer toward UIN and COU, so have opted to 
keep a vicinity mention in those TAFs through the afternoon while
I've left the STL metro TAFs dry for much of the afternoon.



Saint Louis     73  85  73  84 /  30  30  30  80 
Quincy          70  79  68  73 /  60  60  80  80 
Columbia        70  80  69  77 /  50  50  60  80 
Jefferson City  71  82  70  79 /  40  40  50  80 
Salem           69  83  70  86 /   5   5   5  60 
Farmington      68  82  68  85 /  10  20   0  60 


MO...Flash Flood Watch from Saturday evening through late Sunday 
     night for Audrain MO-Boone MO-Callaway MO-Knox MO-Lewis MO-
     Marion MO-Monroe MO-Montgomery MO-Pike MO-Ralls MO-Shelby 

IL...Flash Flood Watch from Saturday evening through late Sunday 
     night for Adams IL-Brown IL-Pike IL.

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