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

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000
FXUS63 KEAX 172350
AFDEAX

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
550 PM CST Sun Dec 17 2017

.Discussion...
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 00Z TAFS through 00Z Monday Evening)
Issued at 528 PM CST SUN DEC 17 2017

Although there are pockets of clearing within the low-level
stratus deck around the terminal areas, satellite trends as well
as model soundings are indicating the cloud cover sticking around
well into the overnight hours. As a trough in the region breaks
down, the stratus is anticipated to dissipate as well, leaving
clearing skies behind. However, the timing of clearing looks to
occur around dawn Monday, and given the timing, trapped low-level
moisture that won`t have had enough time to clear out, and moist
grounds from today`s rain, the stage looks to be set for fog to
develop for a few hours in the morning. By midday Monday, the
clouds and fog are expected to have dissipated, leaving VFR
conditions to prevail for the remainder of the TAF period. Light
and generally variable winds will dominate overnight, becoming
southwesterly at around 10 knots or so by Monday afternoon.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
MO...NONE.
&&

$$

Discussion...Barham
Aviation...lg



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