Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 162100

Area Forecast Discussion
National Weather Service Saint Louis MO
400 PM CDT Fri Mar 16 2018

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 351 PM CDT Fri Mar 16 2018

Despite a relatively dry day for much of the region we are still
anticipating a round of showers and a few thunderstorms from the
remainder of the afternoon into evening. The surface low was located
in north central KS at mid afternoon with an occluded front/dryline
extending southeast across southwest MO with the warm front then
drapped southeast into central AR resulting in a narrow warm
sector. Showers and thunderstorms have been developing across
western MO ahead of the surface front along the leading edge of
large scale ascent associated with a negatively tilted short wave
rotating east northeast through the Plains upper trof. The current
thinking is this area of showers and a few thunderstorms will
continue to expand and move into central MO later this afternoon,
progressing east across the entire area this evening as the short
wave rotates east-northeast. Thus the precipitation will largely
stay well ahead of the surface low and attendant southward
trailing cold front. Any threat of severe will be through early
evening across central MO with an isolated elevated storm capable
of marginally severe hail. While the surface low will only be in
northwest MO by 06Z, with the exception of some lingering spotty
showers, the main area of precipitation should be east of the
entire area by midnight or so. The surface low should be pretty
close to St. Louis at 12Z Saturday and will pass to the east by
late morning as the entire mid-upper system weakens and moves
east. Increasingly cyclonic flow and CAA in the wake of the
surface low beginning overnight and continuing on Saturday will
support extensive stratus that will keep temperatures a bit chilly
for St. Patrick`s Day.


.LONG TERM...  (Saturday Night through Next Friday)
Issued at 351 PM CDT Fri Mar 16 2018

High pressure centered over the upper Mississippi River Valley will
remain in control of the weather over the area on Saturday night
into Sunday. The area of high pressure is expected to move east to
northern Ohio by Sunday night. An area of low pressure along the
CO/KS line will deepen and the attendant cold front will slowly
push east toward the area. The surface low and attendant cold
front will then push through the area Monday-Monday night, with
the surface low expected to track south of the area. There will
be showers and isolated thunderstorms as the system approaches and
moves through the area.

A second short wave in the wake of the initial system will then
rotate thru the base of a broad trough centered to our east on
Monday night through Tuesday morning. This will bring a chance for
a light rain/snow mix except in far southeast Missouri on late
Monday night into Tuesday morning. A surface high pressure over
the Northern Plains will begin to move toward the area by Tuesday
afternoon and into the area by Wednesday morning. An upper level
short wave will move also toward the region on Wednesday afternoon
and evening. The short wave will most likely only provide the
region with cloudiness, but a sprinkle or two is not out of the
question on Wednesday afternoon and evening. The surface high
pressure will then provide dry weather from late Wednesday evening
into Friday morning.



.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1241 PM CDT Fri Mar 16 2018

Precipitation is at a minimum at midday with some spotty showers
in eastern MO and another area of light rain across west central
IL moving east. I think through 20Z or so any additional
precipitation will be rather spotty as well with VFR flight
conditions continuing. After 20Z a north-south band of showers
and some thunderstorms will both develop and spread into central
MO then progress eastward across the region through the afternoon
and evening. Present expectations are all the precipitation should
be east of the terminals by 03-04Z. Flight conditions with the
band of showers and embedded thunderstorms should be MVFR. All of
this precipitation will be occurring ahead of an advancing low
pressure system which will move steadily from eastern KS across
MO to near KSTL by 12Z. Stratus/MVFR cigs should encompass the
area in the wake of the surface low and attendant cold front
overnight into early Saturday morning.


A few sprinkles or brief shower could impact KSTL through mid
afternoon with VFR flight conditions prevailing and gusty easterly
winds. Between 23-00Z a band of showers and a few thunderstorms
will move into the terminal and continue until around 03Z. MVFR flight
conditions are expected with this band. After the precipitation
exits there could be a period of MVFR cigs overnight as a warm
front gets close by. Otherwise a surface low and cold front will
move through around 13Z accompanied by a northwest wind shift and
more continuous stratus and MVFR flight conditions.





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