Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 052128

Area Forecast Discussion
National Weather Service Saint Louis MO
328 PM CST Thu Dec 5 2019

.SHORT TERM...  (Through Late Friday Night)
Issued at 324 PM CST Thu Dec 5 2019

The approaching surface cold front, driven by the mid level
shortwave, will drive light rain into the region late tonight into
early Friday morning. The majority of this rain will stay south
of I- 70, though brief periods of light rain cannot be ruled out
along the Columbia-St. Louis-Salem, IL line. Both the front and
light rain exit the area Friday morning, leaving the remainder of
Friday dry. Behind the front, northerly winds will advect cold air
into the region. This cold air advection combined with lingering
low stratus will help keep temperatures much cooler than recent
days, with highs mostly in the 40s. Temperatures on Friday will
peak in the around sunrise before slowly falling through the
morning hours, then remaining steady during the afternoon.


.LONG TERM...  (Saturday through Next Thursday)
Issued at 324 PM CST Thu Dec 5 2019

A rapidly moving surface high builds into the region in the wake of
Friday`s system and keeps the weekend largely precipitation free. As
it moves out of our area Saturday winds will veer to the south and
we will return to above normal temperatures in the 50s Sunday
through Monday.

As the weekend surface high continues eastward out of the Midwest
another surface low, attached to a deepening mid level trough, edges
into the region Sunday night. This system will provide our next
round of precipitation starting Sunday night into Monday night. The
mid level trough deepens as it moves through the CWA on Monday, and
steers the surface low out of the area to the northeast. As the
surface low lifts out of the area Monday parallel to the slow moving
cold front, guidance suggests a lingering chance of precipitation
across the area through Monday night. Some of this precipitation may
end as light snow before moving out of the area completely. A
surface high building into the area in the wake of this strong
surface low will keep the forecast precipitation free Tuesday
through the end of the period.

The passage of this cold front continues to mark a significant shift
in temperatures as highs Tuesday through the end of the period will
top out in the mid 20s to mid 30s. While this isn`t particularly
chilly for December, it is about 10 degrees below normal and will
feel cool after the past several days of above normal



.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1112 AM CST Thu Dec 5 2019

Current VFR conditions are forecast to degrade tonight as an
approaching cold front and precipitation shield move into the
area. Mid level clouds will continue to build to the northeast
through the day ahead of the rain. Clouds will build in at MVFR
heights toward dawn Friday and persist until the afternoon hours
when widespread clearing will occur. Brief periods of IFR
conditions are possible through the remainder of the TAF period.
The cold front will begin to move through KUIN at 09Z and move
through KCOU and the metro terminals around 11Z, producing a
significant wind shift from southwesterly to northerly and an
increase in wind speed to 10-15 mph. Some gusts are expected at
KUIN on the order of 20-25 mph. The northern edge of the light
rain shield is expected to approach the KCOU-KSTL line before
moving out to the southeast Friday morning.


VFR conditions are forecast to prevail even while mid level clouds
build in through the day and evening associated with the
approaching light rain shield. A cold front will move through the
terminal tomorrow morning around 12Z bringing an increase in
wind speed to 10-15 mph, a wind shift from southwesterly to
northerly, and an MVFR cloud deck. Behind the front IFR
ceilings are possible but at this point have held off on
including them in the TAF due to low confidence of IFR reaching
into the metro. Ceilings are expected to improve dramatically
during the afternoon as dry air advects in from the northwest and
ceilings rise back up to VFR conditions.



Saint Louis     42  44  30  49 /  40  30   0   0
Quincy          33  38  25  46 /   5   0   0   0
Columbia        36  42  28  50 /  40  10   0   0
Jefferson City  38  43  28  52 /  60  30   0   0
Salem           44  48  29  47 /  50  40   0   0
Farmington      44  49  29  51 /  90  70   0   0




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