Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 212336

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
636 PM CDT Wed Mar 21 2018

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 307 PM CDT Wed Mar 21 2018

Tonight will be cold again with below normal temperatures as a
surface ridge moves through our area. This will lead to good
radiational cooling as most of the clouds dissipate this evening,
while the wind becomes light. Mid level clouds will spread into
our area tomorrow due to low-mid level warm air advection over a
developing warm front. It appears that an area or band of light
showers will move southeastward through parts of our area on
Thursday. The operational GFS model looks a little too quick
bringing precipitation into our area late tonight and Thursday
morning as the boundary layer will initially be quite dry. Its
QPF also looks a little bullish and favor the weaker solution of
the ECMWF model.


.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 307 PM CDT Wed Mar 21 2018

There may be an area or band of light showers dropping
southeastward through east central and southeast MO and southwest
IL Thursday evening. More significant showers along with a few
storms will ramp up Friday afternoon and night as an upper level
trough and an associated surface low approach, while a strong
southwesterly low level jet brings increasing low level moisture
into our area. It appears that the surface low will track from
northwest MO late Friday night southeastward into southern IL by
Saturday afternoon. Any wintry precipitation should be north and
east of our forecast area with the most widespread and persistent
liquid precipitation left of the track of the surface low across
northeast MO and west central IL. The showers will shift east of
our area by Saturday evening with colder temperatures Saturday
night behind the low pressure system. Another round of showers
will spread eastward into parts of central and eastern MO late
Sunday night ahead of another low pressure system developing in
the Lee of the Rockies. A prolonged period of showers and a few
storms will begin on Monday and continue through Tuesday night
due to an active southwest flow, and as a strong cold front drops
slowly southeastward through our area coupled with abundant low
level moisture south of the front.



.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 630 PM CDT Wed Mar 21 2018

VFR flight conditions are expected tonight. Residual diurnal cu
will continue to dissipate this evening with surface high pressure
dominating tonight. Mid-high clouds in northwest flow will begin
to spread into the area during the overnight hours.

VFR flight conditions are expected to again dominate on Thursday.
Clouds will continue to increase within the northwest flow aloft
as surface high pressure slowly slides to the east. Cig heights
will be lowering during the morning to 5000-8000 feet with a band
of showers impacting parts of eastern MO and western IL during the
morning and afternoon hours.


VFR flight conditions are expected through the forecast period.
Residual diurnal cu will dissipate this evening with surface high
pressure dominating. Mid-high clouds will be on the increase on
Thursday morning as high pressure retreats to the east. Showers
could impact the terminal in the afternoon with Cig heights
lowering to 5000-8000 feet.





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