091 
FXUS63 KLSX 240929
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
329 AM CST Tue Nov 24 2020

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 320 AM CST Tue Nov 24 2020

A strong upper level trough is digging into the Four Corners region 
with a deepening low centered over western Kansas. The trough 
will push eastward today, increasing divergence and vorticity 
advection across the region, further deepening the surface low 
over the Plains. The deepening surface low will in turn intensify
the southerly flow across the mid-Mississippi Valley, providing 
low level warm and moist advection, pushing precipitable water
across the area to 1.0 to 1.25 inches by tonight. This 
combination of deep moisture and ample forcing for ascent will be 
enough to bring scattered showers into Missouri this afternoon, 
becoming widespread on both sides of the river this evening and 
overnight.

Meanwhile, more robust convection back along the cold front will 
build into southwest Missouri tonight before moving into southern 
sections of the forecast area in the pre-dawn hours. Given strong 
system dynamics, it's possible that a few of these storms become 
strong enough to produce damaging winds given sufficient 
instability. However, most high res guidance shows the frontal 
convection racing ahead of the front as it moves through southern 
Missouri tonight. With that, it looks like there is only a narrow 
window in which this convection will have sufficient instability to 
produce severe storms before running into the widespread warm sector 
precipitation. I'm not especially confident that window will align
anywhere in our CWA, but the SPC marginal risk seems appropriate 
given the conditional threat for severe storms.

As we move into Wednesday, much of the overnight precipitation is 
expected to move east of the area before the cold front itself 
sweeps through the region later in the day. With a lull in 
precipitation ahead of the fropa, much of the guidance does build 
limited instability into the region, mainly focused on our 
Illinois counties. The forcing along the front, combined with the
instability ahead of the front, may be enough to initiate yet 
another round of scattered showers and storms. Storm dynamics 
will again be quite strong, supporting another chance for severe 
storms. Along with damaging winds, I can't rule out a few, brief 
tornadoes before the front clears the area in the afternoon.

BSH

.LONG TERM...  (Wednesday Night through Monday)
Issued at 320 AM CST Tue Nov 24 2020

Long term discussion will be updated shortly.

BSH

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1041 PM CST Mon Nov 23 2020

Light showers will remain possible through the night with mainly
VFR or high MVFR conditions. A more steady rain will move into
KUIN and KCOU during the morning hours and the St. Louis area
terminals during the afternoon and evening hours. Conditions will
drop to low VFR or MVFR with this rain. Generally light winds 
early in the period will turn out of the south by late evening and
will gust around 20KTS by mid morning on Tuesday. 

SPECIFICS FOR KSTL: 

While there is some chance for rain during the overnight and
morning hours, conditions are expected to be mainly dry and VFR 
until late afternoon before rain moves into the area and 
continues into the evening. Conditions will drop to low VFR or 
MVFR with this rain. Generally light winds early in the period 
will turn out of the south by late evening and will gust around 
20KTS by mid morning on Tuesday. 

Britt

&&

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

$$

WFO LSX