Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 111142

Area Forecast Discussion
National Weather Service Topeka KS
542 AM CST Sat Nov 11 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 303 AM CST Sat Nov 11 2017

A low amplitude upper level trough embedded within the zonal flow at
the mid and upper levels of the atmosphere, will move east across
the central plains Today. Ahead of the approaching upper level
trough, a lee surface low located across southeast CO early this
morning will move east-southeast across northern OK and extreme
southern KS. residual moisture, with dewpoints in the upper 40s
across western OK will advect northward ahead of the surface
low/trough as it moves east along the OK/KS border. Also, moisture
advection at 850mb with 4 to 5 deg C dewpoints advecting northeast
across the CWA through the afternoon hours. The low-level moisture
advection northward into a shallow cool airmass across eastern KS
will cause enough isentropic lift for widespread drizzle to develop
from west to east across the CWA during the morning hours. The
drizzle will continue through most of the afternoon as the 290K
pressure surface shows the isentropic lift increasing across the CWA
during the afternoon hours. Forecast soundings remain unsaturated
above 750mb through the day, thus despite the weak ascent ahead of
the H5 trough axis there will be no larger rain drop production. I
expect a prolong drizzle event which may accumulate 0.01 to 0.03
inches of QPF. Therefore, I have inserted POPs with the drizzle.
Although some location may only see trace amounts of QPF.

The low clouds and drizzle will keep temperatures cool with highs
only reaching the lower to mid 40s across much of the area. There
could be some light fog developing through the day but visibilities
should remain above 3 miles.

Tonight, the upper trough will begin to amplify as it moves east
across MO. A weak surface cold front will push southeast across the
CWA and the better low-level isentropic lift will shift east of the
CWA during the evening hours. The cloud cover will keep overnight
lows in the upper 30s to lower 40s.

.LONG TERM...(Sunday through Friday)
Issued at 303 AM CST Sat Nov 11 2017

Models are in good agreement with flow aloft being largely zonal
across the CONUS. The main challenges the timing and depth of the
low level moisture and how warm the mid levels will be ahead of
shortwaves and their associated Pacific cold fronts.

Sunday brings good mid-level subsidence behind tonight`s upper wave
with surface high pressure spreading east through the upper Missouri
Valley. This brings clearing skies and weakening winds late in the
day, though the details of the clearing and wind speeds will need to
be watched. A later clearing (and a delayed onset of high cloud
overnight) and more persistent weak winds would provide a good
environment for radiation fog Sunday night into Monday morning. Warm-
air advection/isentropic lift steadily increases Monday afternoon
into Tuesday as the upper wave off the Pacific Northwest coast this
morning enters the northern Rockies Monday night and the northern
Plains Tuesday. The mid-levels again are rather warm and dry on
westerly flow and again look to keep any precipition in the drizzle
or light rain variety Monday night into Tuesday, but a strong low
level jet ahead of the wave and cold front brings 850mb dewpoints to
around 12C Tuesday night for elevated CAPE around 500 J/kg and high
chances for wetting precip for eastern Kansas. Much of Wednesday and
Thursday looks dry until the next wave approaches. Models continue
to show a wide spread of timing with this wave, though moisture
quality from even the slower ECMWF is not to the levels of Tuesday
night. Have kept precip chances much lower and in mainly eastern
areas for Thursday and Thursday night.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 537 AM CST Sat Nov 11 2017

VFR stratus across the terminals will lower to MVFR ceilings through
the morning hours. Patchy drizzle will develop through the mid
and late morning hours. This afternoon ceilings will drop to low
MVFR to IFR and the drizzle will become more widespread. The
drizzle should end during the mid and late evening hours. However,
expect VFR ceilings through the night. A weak cold front will
switch winds to the northwest under 10 KTS after 9Z SUN.




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