Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 182102

Area Forecast Discussion
National Weather Service Saint Louis MO
402 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.


.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.



.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1245 PM CDT Fri May 18 2018

Upper low continues to provide support for showers with isod/sct
TS thru this afternoon. Precip shud gradually move east and
diminish this evening. Cigs will be slow to improve at KSUS/KCPS,
tho if enuf breaks in the clouds can develop, enuf mixing may
occur to at least lift the cigs into MVFR category.

Believe at least light fog will develop tonight with light winds
and ample moisture for locations that receive rain today. Have low
confidence on how low visbys will drop overnight, but this may
lift as a stratus deck on Sat morning.

SPECIFICS FOR KSTL: Rain continues this afternoon with slow
improvement to cigs. Expect some fog to develop overnight, which
may lift as stratus on Sat morning. Details will need to be added
as confidence increases, but going cigs Sat morning may be too



Saint Louis     65  87  68  90 /  40  10  20  30
Quincy          62  83  60  83 /  30  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 /  60  10  20  30
Farmington      62  86  65  89 /  40  20  20  30




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