014 
FXUS63 KLSX 180147
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
847 PM CDT Sat Aug 17 2019

.UPDATE...
Issued at 841 PM CDT Sat Aug 17 2019

Scattered storms have developed along a convergence zone running
from roughly Waterloo to Salem, IL. Storms are expected to persist
through the next few hours before the atmosphere becomes capped,
limiting storm chances into the early morning hours. Beyond that,
attention turns to yet another round of morning storms moving in
from the NW. Expectations for this round of storms remain the 
same as described in the previous discussion.

BSH

&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 407 PM CDT Sat Aug 17 2019

Focus thru the period remains precip chances. 

MCV continues to slowly move east thru the region this afternoon. 
Low level convergence is progd to increase this afternoon across 
eastern and into southern portions of the CWA. Models suggest 
southern portions of the CWA will remain capped with warmer low 
level temps above the mixed layer. However, further east, the MCV 
and stronger low level convergence should help erode this cap for a 
few storms possible this afternoon. Any storms that do develop 
should quickly move out of the CWA by early evening. Any storms that 
develop should remain below severe limits, but can not completely 
rule out an isolated severe event with damaging wind as the most 
likely threat given the better low level lapse rates. 

Believe the bulk of tonight will remain dry, but have kept some 
lingering low PoPs. Expect a decaying MCS to reach western portions 
of the CWA around 09z or later and continue moving east into Sun 
morning. Can not rule out a severe threat with these storms. Large 
hail should be the main threat with steep mid level lapse rates and 
what should be a decoupled boundary layer. Uncertain how much this 
complex will hold together, but should weaken by late morning as the 
area begins to become capped. Another round of storms is possible 
during the afternoon into the evening hours as the cold front 
approaches. Going PoPs are likely on the low side, but with lower 
confidence in model solns, will hold off with higher PoPs until 
better agreement. 

Temps tomorrow will be challenging as convective debris will likely 
at the very least delay heating. Regardless, with the region within 
the warm sector, have trended close to the prev forecast and above 
the warmer MOS.

Tilly

.LONG TERM...  (Monday through Next Saturday)
Issued at 407 PM CDT Sat Aug 17 2019

The period will start off quite warm with the potential for heat 
indices to exceed 100F in some places Monday with widespread 100-
105F indices for Tuesday. The active pattern may continue through 
the week with several factors coming into play. 

An upper level ridge will remain parked over the southern U.S. 
through about Tuesday, while a well defined upper cyclone continues 
to rotate in a nearly stationary fashion just west of the Hudson Bay 
in Canada. Between these two features will be quasi-zonal flow, 
which will only meander slightly north/south from day-to-day. This 
is a conducive setup for small, quick-moving shortwaves to press 
west to east with the zonal flow. 

Working down through the mid levels to the surface, a southeast U.S. 
ridge will result in warm, moist southerly flow from the western 
gulf region into the eastern plains and Midwest. A cold front 
attempts to push southeast through the region, but seems as though 
it may stall as forward progress is more so voided by the stronger 
southeastern ridge and southerly flow. 

Both the upper ridge and mid-level ridge over the the southeastern 
CONUS intensify in tandem Tuesday. Upper height rises build in from 
the west just as southerly flow pools low to mid-70s dewpoints along 
the stalled boundary. As high reach well into the 90s, this could 
pan out to be the grossest day of the week with a stagnant airmass 
and heat indices climbing near 105F for a large portion of the area. 
There is a subtle hint at a weak upper shortwave passing around the 
eastern periphery of the ridge just to the north. This would 
introduce at least a slight chance for showers and storms Tuesday 
afternoon north of I-70. 

The upper ridge begins to break down through the midweek period, as 
the upper cyclone begins to move southeast out of Canada through the 
late week period. Guidance is quite messy with several weaker waves 
passing through west-to-east flow, along with weak surface 
boundaries that tend to wash out with southward travel. There is 
more likely to be a relief in temperatures from midweek on as a cold 
front settle just south of the area with the aid of a surface high 
building in late in the week. This may also be the best chance for a 
rain-free forecast Friday into Saturday with highs back in the low 
to mid-80s.

Maples

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 627 PM CDT Sat Aug 17 2019

Forecast this evening is a bit less murky than what we've been 
dealing with the last few night, but some uncertainty remains. 
Long story short; VFR conditions should persist outside of 
scattered storms, which are most likely tomorrow morning.

That said, a cluster of storms has just developed SE the STL 
area. These storms are expected to persist into the evening as 
they push east out of the area, remaining clear of the terminals.
We'll then see a lull in storm activity in our area for much of 
the night as yet another round of showers and storms develop to 
our northwest. Like last night, these storms are expected to drift
to the SE in the morning hours, likely impacting a few of the 
terminals. However, these storms are expected to develop quite a 
bit farther north than what we saw last night, and I'm not 
confident they'll make it all the way to the STL metro. On top of 
all this, LLWS is looking more likely at COU and UIN.

Storm chances persist trough much of tomorrow, but they largely 
hinge on how the morning storms play out. Given the uncertainty
regarding tomorrow's storms, and a general lack of forcing
tomorrow, I'm not confident enough to put any mention of storms in
the TAFs beyond the morning.

BSH

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     75  91  74  91 /  20  40  20  30 
Quincy          72  84  71  87 /  60  60  30  20 
Columbia        72  87  71  90 /  50  70  30  30 
Jefferson City  73  88  70  91 /  40  50  30  30 
Salem           72  90  71  90 / 100  30  20  20 
Farmington      71  90  68  91 /  20  30  20  20 

&&

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

$$

WFO LSX