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

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FXUS63 KEAX 051017
AFDEAX

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
417 AM CST Mon Dec 5 2016

.Discussion...
Issued at 409 AM CST MON DEC 5 2016

Dense fog has formed across the area underneath a surface ridge
where light winds and a saturated surface has aided in widespread
development. A Dense Fog Advisory has been issued across much of the
eastern CWA through the mid morning hours. Fog should eventually
erode as the surface ridge continues to push eastward and daytime
heating lends to mixing within the lower levels. Aside from reduced
visibility, possibly degrading to a quarter mile in most prone
areas, a light glaze is possible across roadways as temperatures
continue to cool to below freezing.

A break in the activity will establish briefly today as zonal flow
builds aloft, prior to a quick turn in events beginning late
tonight. A cut off low now centered over Mexico will push to the
northeast this evening into the lower Mississippi River Valley as a
shortwave trough. This will form a surface low near the Gulf Coast
with resulting precipitation possibly extending as far north as
central Missouri. Thus, light rain is possible for the southeastern
CWA with only minimal rainfall totals through Monday night.

The beginnings of a significant pattern change are now visible on
water vapor imagery in the form of a deepening upper level trough
positioned over the Northern Rockies. Energy from its parent upper
low over Saskatchewan will push this feature southeast with further
strengthening expected by this afternoon. A surface low will form
over the Northern Plains by the evening hours and will send a cold
front and a resulting arctic air mass over the region late tonight.
This will turn slightly above normal temperatures Monday in the lower
50s to frigid temperatures by the latter half of the week. Overnight
lows will drop into the 20s for most areas Tuesday night with similar
readings for Wednesday high temperatures. The coldest night of the
week looks to occur Thursday night, where single digit temperatures
are possible by early Friday morning. It is also during this time
that wind chill values could approach or go below zero degrees for
most areas.

The lingering cold air mass will set the stage for the potential
first significant winter weather event of the season. Models continue
to show good agreement in the formation of a broad upper wave
settling across the Central Plains by Wednesday afternoon. Sufficient
ascent and moisture ahead of this wave are making for an increasingly
likely setup for accumulating snowfall across the area. Though models
show agreement both spatially and temporally with the upper wave,
they do show some disagreement in the magnitude of the resulting
snowfall totals. The ECMWF has been the most consistent of its
advertised solution over the last several days and is also the most
aggressive with available moisture. Both the NAM and GFS produce more
conservative solutions, though accumulating snowfall does appear to
be the likely scenario at this point. The thermal profile will
support all snow from the onset of the event, thus ice formation will
not be an issue. Also, with the air mass as it is, snow ratios will
remain rather high during the extent of the event as well. Thus, any
moisture realized will result in higher snowfall amounts through the
duration of the event. The existing dry air mass below 850 hPa will
take some time to saturate, though once it does, snowfall totals may
approach between 1 to 2 inches, with locally higher amounts possible.
At this time, the favored region will parallel the I-70 corridor
in addition to points south of the Kansas City metro. Lesser amounts
between a dusting to 1 inch are possible as far north as the IA/MO
border. This scenario may easily change, especially considering the
synoptic nature of the unfolding event. Depending on the available
moisture and residence time of the upper wave, forecast snowfall
amounts may need to be reduced in subsequent forecasts.

By the weekend, zonal flow will return aloft and temperatures will
slowly return to near normal by the late weekend. The next chance of
precipitation may then hold off until the early week given the
stagnant pattern, so have removed precip chances until the late
period.


&&

.Aviation...(For the 06Z TAFS through 06Z Monday Night)
Issued at 1053 PM CST SUN DEC 4 2016

The main challenge with this forecast is the potential for fog
through a few hours after sunrise. To this point in the night, the
fog has been fairly patchy. But with a weak pressure gradient roughly
along and south of the Missouri River, it looks more likely that more
widespread fog is possible with patchy areas of dense fog. This would
mainly impact the KIXD terminal, which is already seeing visibilities
1/2sm or lower. Short term model guidance suggest the weakness in
the pressure gradient will shift southeast late tonight, resulting in
a bit more mixing/wind at the terminals. So it`s possible conditions
at IXD may be at their worse now and then improve some as winds may
increase slightly before sunrise. Once fog lifts for good by mid
morning, VFR conditions are expected through the remainder of the
forecast.


&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
MO...Dense Fog Advisory until 9 AM CST this morning for MOZ005>008-
     014>017-022>025-030>033-037>040-043>046.

&&

$$

Discussion...Welsh
Aviation...CDB


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