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

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FXUS63 KEAX 111132

National Weather Service Kansas City/Pleasant Hill MO
532 AM CST Wed Jan 11 2017

Issued at 345 AM CST WED JAN 11 2017

...Impactful winter storm increasingly possible this weekend...

Today - Thursday

A surface ridge is currently sliding to the east of the area with
zonal flow in the upper levels. The southerly winds will strengthen
today as a surface low from the Rockies approaches the area. Wind
gusts up to 30 mph are possible today, especially south of I-70.
In addition, this will advect well above normal temperatures into
the area. Highs are forecast to be in the mid 60s along and south
of I-70, mid 50s along HWY 36, and mid 40s along the MO/IA border.
The warm temperatures will be short- lived, however, as a strong
cold front sweeps through the area tonight bringing much colder
temperatures. The frontal passage will also bring precipitation
chances starting Wednesday afternoon through Thursday morning.
There is still some model disagreement regarding precipitation
location though. The GFS has very little precipitation in the
forecast area, whereas, ECMWF and NAM produce precipitation for
most of Wednesday night through early Thursday morning. All models
show though that generally areas south and east of I-35 are the
most likely to see precipitation. Any precipitation that does fall
will start out as drizzle first but as temperatures drop at the
surface, the drizzle will transition to freezing drizzle. Even
though a cold front will have moved through and dropped surface
temperatures we will still have an elevated warm layer thanks to
the surface high in the western Atlantic advecting warm
temperatures into the area thus giving us freezing drizzle. Very
little accumulation is expected with this activity though. The
rest of Thursday and Thursday night will be quiet with lows
dropping into the teens and low 20s.

Friday - Monday

The main focus of the forecast period is this weekend, as a
potential winter storm looks increasingly likely. For the first part
of the weekend there is still decent agreement with the GFS, ECMWF,
and Canadian regarding some broader features. A positively tilted
closed upper level low will slowly move toward the area from the
southwestern US and become negatively tilted by Saturday night. In
addition, models agree on some surface features like the
aforementioned western Atlantic surface high advecting warm,
moist air into the area, the previously mentioned surface cold
front stalling near the MO/AR border Thursday through the weekend,
and strong arctic surface high moving in over the northern Plains
advecting cold surface temperatures. Finally, all models depict
an elevated warm layer over most of the area for the entire
weekend. All of these variables add up to freezing rain being the
primary precipitation type with sleet possibly mixed in during
certain times. The onset time right now looks like early Friday
morning along HWY 54, along I-70 some time after noon, and along
the MO/IA border by midnight. If this comes to fruition the
evening commute would be impacted. The chances for freezing rain
would then continue through Sunday with a potential break Saturday
afternoon. Precipitation then is expected to change over to rain
by Monday morning. While there is some consensus with the models,
this solution is contingent on surface temps. Right now, am
leaning more toward to the cooler ECMWF temperatures due to the
reinforcing arctic surface high and cloud cover. The GFS and
Canadian have the surface freezing line entering the far southern
portion of our area Saturday morning and remaining in our area for
the rest of the weekend, slowly retreating north, whereas, the
ECMWF keeps the surface freezing line just south of the forecast
area through Sunday night. If the GFS and Canadian solutions come
through our southern border would see a transition to rain
Saturday afternoon and then back to freezing rain overnight. On
Sunday, the surface freezing line is expected to retreat north
through the area, but the question mark surrounds the timing.
Again, the GFS and Canadian are warmer and move the surface
freezing line north quicker than the ECMWF. This will affect when
we see the transition from freezing rain to rain. At this time,
all models depict rain for the entire forecast area at least by
late Monday morning. And again, have leaned a little more toward
the cooler ECMWF solution for the transition time. In addition to
the surface temperature differences, the precipitation coverage
also varies between the models. The GFS is a little slower to move
precip into the area than the ECMWF and Canadian on Friday and
the ECMWF and GFS show potential for a break in precipitation
during the day Saturday for much of the area. Despite the
differences, no model is dry. As far as when this system will
completely exit the region, right now, models suggest some time in
the Tuesday time frame.

While there is increasing confidence in this winter storm event,
remember there is no complete model consensus and there is still
time left for things to change, so stay tuned...


.Aviation...(For the 12Z TAFS through 12Z Thursday Morning)
Issued at 530 AM CST WED JAN 11 2017

VFR conditions will prevail for the first 12 hours or so of the
forecast period and then ceilings will drop to MVFR around dusk as
a cold front moves through the area. Before the cold front passes
though, the biggest concern is the low-level wind shear around 45
kt at 2kft. Like yesterday, there is not a whole lot in the way of
directional shear but the speed shear is strong enough to cause
concern. The LLWS threat will diminish for the forecast area after
18Z. The gusty surface winds will stick around though through the
evening. Again, a strong cold front will pass through the area
shifting winds to the north and bringing MVFR ceilings into the
entire area around dusk. The short-term and long-term models all
agree on the MVFR ceilings and their timing. In addition, there
are chances for drizzle this afternoon and then freezing drizzle
overnight, mainly south and east of I-35. Very little
accumulation is expected.




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