Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 011114
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
514 AM CST Thu Dec 1 2016

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 310 AM CST Thu Dec 1 2016

Mid/upper level low pressure finally moving over the Great Lakes
region, which is allowing the area to dry out. Skies are mostly
clear although far northeast KS may have a few clouds move through
this morning. Winds have decreased with the relaxing pressure
gradient, but the surface has not fully decoupled given the lack of
a strong surface high. This along with cooler air mass will allow
lows to drop into the lower to mid 20s. Today winds will continue
out of the northwest around 5 to 10 mph, and highs will reach the
40s. The coolest temperatures will reside across far northeast KS
especially if the stratus can manage to work into that area. Tonight
there may be some high clouds that move over the region otherwise
most locations will be mostly clear. The winds again will be light
therefore lows should end up generally in the mid to upper 20s. The
only exception to that will be in east central KS where some stratus
may build in causing lows to remain in the 30s.

.LONG TERM...(Friday through Wednesday)
Issued at 310 AM CST Thu Dec 1 2016

Friday a positive tilt upper level trough across the western US will
shear apart with the northern portion of the upper trough moving east
into the northern and central high plains. The southern half of the
upper trough will amplify into a closed upper low and dig south-
southeast into northern Mexico. We may see high clouds increase late
in the day and highs will range from the mid 40s across the northern
counties of the CWA to around 50 along the southern counties.

Friday night through Sunday, the 00Z GFS shows the northern H5
trough moving east across the plains. There will be enough ascent
ahead of the open H5 wave along with residual moisture for light
precipitation to develop after midnight across the southwest
counties of the CWA and spread northeast across the CWA during the
morning hours. The NAM and GFS forecast soundings show vertical
temperature profiles below freezing and if precip reaches the
surface there should be quick wet bulb cooling for light snow. I
cannot rule out a dusting of snow in the southwest counties during
the morning hours of Saturday. The northeast counties may only see
snow flurries since the low-level look much drier. The snow  will
probably change back to rain during the mid morning hours as
surface temperatures rise through the mid and upper 30s. Expect
periods of light rain through the afternoon hours. As temperatures
cool during the early evening some of the lingering light rain may
change or mix with snow before ending as the H5 trough shifts east
into the upper midwest and mid MS river valley late Saturday night.
Meanwhile the closed upper low over northern Mexico will be tracking
due east. The 00Z run of the ECMWF is more amplified with the upper
trough moving east across the plains but advects slightly warmer air
northward at the surface and at 850mb, thus if the ECMWF were to
verify we may see a brief rain and snow mix Saturday morning but
everything will change over to rain by the mid morning hours with
periods of rain through Saturday night into Saturday night. If
temperatures cool into the mid 30s Saturday night across the
northern counties of the CWA, then some snow may mix in with the
rain. The ECMWF is slower moving the H5 trough east so the rain will
linger through morning hours of Sunday and will end from west to
east across the CWA on Sunday.

Monday through Tuesday, a deep upper trough will dig southwest into
the western US and amplify, this will cause the closed upper low
over northeast Mexico to be lifted northeast across TX and then
across the lower MS river valley. The ECMWF keeps the stronger
ascent and moisture southeast of the CWA. The 00Z GFS lifts the
upper low a bit farther north, across northeast TX, which will
provide enough ascent for light rain or snow to develop across the
CWA Monday night into Tuesday. Looks like any accumulations of snow
will be light across north central and northeast KS, if the GFS
forecast solution proves to be more accurate.

Tuesday night through Wednesday night, the amplified upper level
trough across the western US will lift northeast into the central
plains. The first real intrusion of Arctic air into the plains will
move southward across the state of KS Tuesday night. As the Upper
Trough lifts northeast into the plains a heavy snow band will
develop across eastern CO and western KS and shift east-northeast
across north central and portions of northeast KS. The exact track
of the heavy snow band remains uncertain and will depend on how the
lead H5 trough translate northeast across western KS into NE. The
eastern counties of the CWA may start out with light rain during the
early morning hours of Wednesday ahead of the Arctic front but the
shallow cold airmass will rapidly push southeast and change the rain
over to freezing rain and then to sleet and to light snow. The
western and northern counties of the CWA will probably remain all
snow with the potential for significant snow accumulations. The 00Z
GFS has a less amplified solution but does show widespread snow
developing across CWA behind the arctic front Tuesday night into
Wednesday morning. Stay tuned to later forecast, since this is the
first time both the ECMWF and GFS model solutions are close to one
another for Tuesday night into Wednesday.

Thursday will feel like winter with highs in the 20s according to
the GFS. The ECMWF looks much colder and highs only reaching into
the teens. There will be a stiff north wind, so wind chills will
feel much colder. If there is snow cover Thursday night, overnight
lows may drop into the single digits or near zero in some locations,
provided skies clear and winds have diminished.&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1125 PM CST Wed Nov 30 2016

VFR conditions are likely through the TAF period with west winds
generally less than 10 kts.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 513 AM CST Thu Dec 1 2016

VFR conditions expected through the taf period.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Sanders
LONG TERM...Gargan
AVIATION...Sanders


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