Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 161758

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1258 PM CDT Fri Mar 16 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 237 AM CDT Fri Mar 16 2018

Stalled warm front across southern portions of forecast area to
remain anchored in this area, while spotty WAA showers continue to
track east north of boundary across eastern MO and west
central/southwest IL through 09z.

In the meantime, main surface low and upper level low over
western Kansas to begin lifting east northeastward through region
today. Will see activity currently in that area increase in
coverage as low level moisture transport increases on nose of low
level jet. But it too will weaken and peter out as it tracks
eastward through forecast area this morning. Winds will pick up
across the area this morning with gusts up to 30 mph possible,
mainly along and north of I-70, as system moves through.

Models still indicating better chances of showers/storms this
afternoon through this evening as stacked system approaches
region. Decent elevated CAPEs in excess of 500 J/kg, especially
across southern half of forecast area. So will see a line of
showers and storms develop and slide east across region. Isolated
severe storms are possible with the main threat being large hail.
Activity to taper off from west to east late tonight.

As for temps today, it will depend on where the frontal boundary is
and precip/cloud coverage. For now highs will range from the low 40s
over northeast MO, as well as west central and southwest IL, while
mid to upper 50s expected over portions of central and southeast MO.
Lows tonight will be in the mid 30s to upper 40s, so precipitation
to remain all liquid.


.LONG TERM...  (Saturday through Thursday)
Issued at 237 AM CDT Fri Mar 16 2018

Rain showers will taper off on Saturday morning while the
weakening PV anomaly responsible for the pcpn simultaneously
moves away from the region and continues diminishing in part due
to the increasing large-scale subsidence from an upper ridge
building across the central CONUS. The combination of this upper
ridge as well as a surface high across the Great Lakes will ensure
quiet weather through at least Sunday morning.

Temperatures will vary across the CWA on Saturday due to the
boundary left behind by the departing surface low. High pressure
building into the Great Lakes on Saturday night pushes the
boundary farther south, leading to overnight lows in the 30s
areawide. Highs on Sunday will rise back into the mid/upper 50s
ahead of the next approaching low pressure system.

By Sunday evening, southwest flow ahead of a low pressure system
centered near the OK/KS/CO/NM borders will bring periods of
SHRA/TSRA to MO/IL, although limited instability will likely
reduce the coverage of TSRA. The low pressure system quickly
becomes stacked over OK/KS by Monday morning but becomes an open
wave again as it moves across southern MO. The highest chances for
precipitation will be when this system moves across the CWA on
Monday, with the highest precipitation chances expected near and
south of I-70. A few snowflakes could briefly mix in with the
rain as precipitation is ending on late Mon night/early Tue
morning. Highs on Tuesday may only reach the mid/upper 40s, which
would be around 10-15 degrees cooler than normal for this time of

Although model guidance depicts a few more disturbances located
across the region in the wake of the Sun/Mon system, these are
currently expected to be much weaker and therefore should produce
increased cloudiness on Tue into Wed rather than precipitation.
Another upper ridge will move towards the region during the end of
the week, but it is forecast to deamplify as it approaches in
response to the effects of an upstream disturbance. Daily high
temperatures will gradually warm each day and should be near to
slightly below normal by Thursday.



.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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