Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 190323
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1023 PM CDT Fri May 18 2018

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 402 PM CDT Fri May 18 2018

Focus continues to be precip chances thru the period.

Upper low, with the vort maxes undergoing Fujiwhara effect, is
expected to slowly pull ENE out of the area over night. The
convection driven precip shud dissipate gradually this evening,
while the more widespread precip may linger beyond Midnight.

Mdls are in fairly good agreement bringing a wrmfnt into wrn
portions of the CWA Sat morning. Some uncertainty remains what
precip will look like around sunrise, but believe the better
coverage will remain west of the CWA. Regardless, have kept slight
chances for wrn portions of the CWA during the early morning hours.
With the wrmfnt lingering in the area, along with potential outflow
boundary, have kept low PoPs Sat afternoon from roughly KCOU to
KFAM. Mdls have different solns, but with ample heating and a s/w
traveling near the fnt, believe there will be enuf mid level cooling
to allow for a few isod storms. If a good outflow pool can develop,
storms may become weakly organized and would likely travel ESE to SE
along the fnt and flank of the upper ridge/CAP. Any storms that do
develop shud dissipate with sunset.

Focus then turns to convection during the evening hours. Expect
storms to develop during the late afternoon across ern KS. These
storms shud grow upscale into a QLCS and track east along the IA/MO
border. The main question will be how far south convection will
persist. Believe convection will confined to the nrn third to
perhaps half of the CWA. This QLCS will have the potential of
producing damaging winds. Mdls suggest the best timing will be for
the complex to enter the nwrn portion of the CWA during the evening
hours and quickly move east, exiting into IL around Midnight Sun.
Have kept chance PoPs going beyond Midnight Sun as redevelopment
appears possible and continuing into Sun morning.

Otherwise, with the rain today and light winds tonight, have added
patchy fog for tonight. That said, coverage may need to be increased
with lower visibilities. While stratus is expected in the morning,
expect clouds to break up with ample insolation thru the bulk of the
day. Have therefore trended twd the warmer guidance on Sat.


Tilly

.LONG TERM...  (Saturday Night through Next Friday)
Issued at 402 PM CDT Fri May 18 2018

Models currently have warm front extending from northeastern MO
southeastward into southeastern IL by 12z Sunday. But this will
depend on MCS development Saturday night/early Sunday morning, as it
will affect where the effective front/boundary sets up by Sunday
afternoon. With decent CAPES in excess of 3000 J/kg and deep layer
shear, a few strong to severe storms are still possible Sunday
afternoon and evening, especially along and north of I-70. The day 3
outlook keeps this area in marginal risk with main threats being
large hail and damaging winds.

Front to sink just south of forecast area by Monday morning but
stall out. This combined with flow aloft becoming more zonal, will
see several more waves of energy slide along boundary through region
with chances of showers and storms through Tuesday. As upper trof
over western US deepens, there is more disagreement among the
extended models on how to handle this system. So for now will keep
chances of showers and storms through remainder of forecast period.

As for temperatures, they will stay above normal through next week.

Byrd

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1010 PM CDT Fri May 18 2018

Showers should shift east of the taf sites by 06Z Saturday as an
upper level disturbance moves east of the region. The cloud
ceiling will likely drop below 1000 feet in the St Louis metro
area late tonight with fog developing due to the recent rainfall
and light surface wind. Stratus clouds and fog will also likely
develop in UIN and COU late tonight. The stratus clouds and fog
will dissipate later Saturday morning. Surface winds will continue
to be weak on Saturday, mainly from a south-southeast direction.
Showers and storms should move into UIN Saturday evening ahead of
a warm front.

SPECIFICS FOR KSTL: Showers should shift east of the STL area by
06Z Saturday as an upper level disturbance moves east of the
region. The cloud ceiling will likely drop below 1000 feet late
tonight with fog developing due to the recent rainfall and light
surface wind.  The stratus clouds and fog will dissipate later
Saturday morning. Surface winds will continue to be weak on
Saturday, mainly from a south-southeast direction, then shift to
a southwest direction Saturday evening as a warm front passes
through the region.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     65  87  68  90 /  40  10  20  30
Quincy          62  83  60  83 /  40  10  60  40
Columbia        61  85  65  85 /  10  20  30  30
Jefferson City  61  86  65  87 /  10  20  20  30
Salem           65  84  65  89 /  80  10  20  30
Farmington      62  86  65  89 /  20  20  20  30

&&

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

$$

WFO LSX



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