Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 161242

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
742 AM 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 12z TAFs through 12z Saturday Morning)
Issued at 731 AM CDT Fri Mar 16 2018

Initial wave of showers and a few storms moving into TAF sites
this morning, then a bit of a break before more significant round
moves in this afternoon. VFR cigs to lower to MVFR with afternoon
round of showers and storms. Otherwise, east winds to remain gusty
to near 25 kts at times til the system moves through this evening.
As low moves through, winds to veer to the southwest then
northwest on backside of system for taf sites along I-70 with MVFR
conditions improving to VFR. As for KUIN winds to remain from the
east through the valid forecast period and IFR cigs.

Initial wave of showers and a few storms moving into metro area
this morning, then a bit of a break before more significant round
moves in after 19z. VFR cigs to lower to MVFR after 00z Saturday.
Otherwise, east winds to remain gusty to near 25 kts at times til
the system moves through this evening. As low moves through late
tonight, winds to veer to the southwest then northwest by 15z
Saturday. Cigs expected to briefly raise back to VFR after 06z
Saturday, before dropping down to IFR by 15z Saturday.



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