Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO

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FXUS63 KEAX 172014

National Weather Service Kansas City/Pleasant Hill MO
214 PM CST Sun Dec 17 2017

Issued at 212 PM CST SUN DEC 17 2017

Currently there is split upper level flow over the US with zonal
flow along the US/Canadian border and a cut off low and broad
ridging over the southeast US. This pattern will continue through
the first portion of the week keeping the area dry with a westerly
wind and temperatures consistently around the mid 50s. The pattern
starts to shift on Wednesday as the cut off low opens up and moves
south of our region as a shortwave trough.  The zonal flow along the
northern US also starts to make a more meridional shift as a deep
shortwave trough moves into the NW US.  This shortwave trough will
create some active weather Thursday and be the start of a very cold
pattern that will set up on the backside of this trough.

The incoming shortwave trough will help initiate cyclogenesis over
the central plains and enforce a strong shot of colder air on the
backside.  The models had been in agreement with a closed surface
low forming east of our region but the most recent solutions have
this cyclogenesis occur right over our CWA keeping most of the
moisture and isentropic accent more over Iowa.  GFS and ECMWF are
indicated there may be enough moisture in place to develop some rain
showers along the cold front Thursday night into Friday morning. The
colder air may help to initiate a rain to snow transition Friday
over northern Missouri but the uncertainty of the low development
and movement will keep any PoPs low and snow chances limited. A
strong blocking ridge will build into the eastern Pacific allowing
very cold arctic air to start to advect south on the backside of
this cold front. There will be about a 20 degree drop in high
temperatures Thursday to Friday with highs barely getting above
freezing Friday afternoon. This cooling trend will continue as
highs progressively get cooler by a 3-4 degrees a day through the
end of the forecast period and into the Christmas timeframe. The
big question will be if a system can move into this colder airmass
and produce winter precipitation. Currently the GFS and ECMWF
have a shortwave trough exit the southern Rockies Christmas eve
that will help enhance an area of mid level frontogenesis over
Northern Missouri. Currently both GFS and ECMWF produce a band of
QPF and snowfall north of I-70. The Canadian also indicates this
frontogenesis but does it south of I-70. With this uncertainty in
placement of precipitation the PoPs have been kept lower, but this
is definitely a system to watch as it will be highly visible
being Christmas eve and would give the area a white Christmas.


.Aviation...(For the 18Z TAFS through 18Z Monday Afternoon)
Issued at 1106 AM CST SUN DEC 17 2017

MVFR ceilings will dominate the region with pockets of IFR
ceilings early on in the period, mainly over MCI and IXD. Once the
IFR ceilings shift to the east the MVFR ceilings look to remain
most of the evening. There will be a window between 22Z and 03Z
that ceilings could possibly raise up to VFR so a TEMPO was added
to MCI to account for this change. Ceilings look to go all MVFR
again around 06Z and remain that way through sunrise when they
will clear out quickly behind a boundary passing through. If the
clouds clear quick enough there is the possibility of fog
formation through the Missouri River valley which may affect STJ
and possibly MCI around sunrise. Once the clouds clear out and all
fog has burnt off by mid morning all terminals should be VFR for
the remainder of the period.




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