Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 182355

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
655 PM CDT Thu Apr 18 2019

.SHORT TERM...  (Through Late Friday Night)
Issued at 357 PM CDT Thu Apr 18 2019

Rain continues this afternoon over east central and southeast
Missouri as well as southwest Illinois. This is occurring in an
area of mid level frontogenesis ahead of deepening trough. Expect
the northwest periphery of the persistent rain to shift to the
southeast this evening as the trough moves southeast into the
Midwest, but the rain will continue across southeast Missouri
into southwest Illinois through the night into tomorrow morning.
This is because both the GFS/NAM are showing the upper trough
deepening and eventually closing off as an upper low over the mid
south. A surface low currently over Mississippi will move
northeast into the Ohio Valley by tomorrow morning. Expect the
rain chances to continue through tomorrow before diminishing on
Friday night as the low begins to move off to the east.

Lows tonight will not drop much with the clouds and rain, so went
with temperatures in the mid 40s.  Highs tomorrow with also be
tempered with clouds and rain chances, especially over the eastern
half of the CWA.  Lows on Friday night will drop back into the upper


.LONG TERM...  (Saturday through Next Thursday)
Issued at 357 PM CDT Thu Apr 18 2019

The weekend is still expected to be dry as an upper ridge builds
over the area in the wake of the upper low.  Highs will climb back
to around 80 degrees on Sunday as 850mb temperatures climb to around
15C.  Next week still looks unsettled as the deterministic global
models and the GEFS show a front becoming stalled over Missouri and
Illinois which will bring scattered showers and thunderstorms.
Temperatures are expected to be mainly above normal along and
south of the front.



.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 629 PM CDT Thu Apr 18 2019

MVFR ceilings over southeast Missouri and southern Illinois are
accompanied by steady light rain this evening. Persistent
precipitation is more likely to be maintained south and east of
TAF sites. KCPS stands the greatest chance at being impacted by
wet conditions tonight into early Friday with slow dissipation in
steadier showers. Further north and west, KSTL and KSUS remain
on the back side of steadier rain with the potential for a brief
passing shower.

MVFR conditions break and lift into VFR west of the aforementioned
sites to broken and scattered ceilings. While the process will be slow,
drier mid-level air will help aid improvement through mid-morning
and early afternoon Friday. Deeper dry air will likely lead to
clearing from west to east from late morning Friday into Friday

The main issue Friday will then be the introduction of gusty
northerly winds ranging 20-30 knots with deeper mixing. Aside from
windy conditions, VFR is expected to be in place over all sites
through Friday afternoon and evening.


MVFR ceilings are slowly breaking from east to west this evening.
Ceilings may periodically bounce between MVFR/VFR as rain slowly
progresses east. A brief shower may pass over the terminal in the
next couple of hours, but any persistent rain should remain east.

A second area of low pressure will slowly move well south and east
of the terminal, but will be effective in keeping MVFR ceilings
in the area. MVFR ceilings will slowly improve to VFR by mid-
morning Friday. As mixing deepens Friday, gusty winds will become
the main issue. Gusts to around 30 knots are possible through
Friday afternoon and evening, before gust dissipate Friday night.

Guidance begins to hint at LLWS late Friday night into early
Saturday morning. However, this comes in the last few hours of the
TAF period, looks borderline on soundings with surface winds
remaining between 10-15 knots and only lasts a few hours. For
now, left this out of the TAF for better analysis as the forecast
matures and later updates getting a better handle on the potential.





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