Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 130535
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1135 PM CST Thu Dec 12 2019

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Friday)
Issued at 240 PM CST Thu Dec 12 2019

A weak surface low currently over Iowa will continue to move
northeast away from the area this evening and overnight. As this
occurs, the associated surface trough over northeast Kansas will
dissipate. Southerly winds will continue to weaken over the next few
hours as this occurs. Temperatures will remain in the low to mid
30s, partially as a result of lingering cloud cover and those weak
southerly winds along the old surface trough. Going into the day
tomorrow, a cold front will slowly move across the area. Southwest
winds and deeper mixing ahead of this front in east-central Kansas
may help temperatures climb into the mid to upper 50s, while
elsewhere highs should generally stay in the low 50s.

.LONG TERM...(Friday night through Thursday)
Issued at 240 PM CST Thu Dec 12 2019

Friday night through Saturday night, an upper level trough off the
Pacific Northwest coast will dig southeast into the the southwest
US. An upper level trough across the eastern US will amplify and
cause a surface ridge of high pressure to build southward across
the central and southern Plains. A weak perturbation embedded in
the northwesterly mid-level flow may provide a slight chance for
light snow or snow flurries Friday night. North winds and low-
level CAA will only allow highs to reach the lower 30s across
north central and northeast KS with mid to upper 30s across east
central KS.

Sunday through Monday, the upper level trough across the
southwestern US will slowly lift east-northeast across the central
Plains on Monday. Light snow will develop from southwest to
northeast across the area Sunday afternoon as isentropic lift
increases at the 280K to 290K theta levels. Through the evening
hours of Sunday, stronger mid-level frontogenesis ahead of the H5
trough lifting east-northeast across the central and southern
high Plains will intensify lift with the potential for CI or CSI
instability to increase. This will provide for good lift to
enhance the DGZ. The 12Z ECMWF forecast a wide band of 2 to 6
inches of snowfall across the CWA with the heaviest snow axis
along the I-70 corridor. The ECMWF solutions shears the upper
trough a bit which may weaken the frontogenetical forcing but
there should be a long duration of moderate snowfall across much
of the CWA Sunday night into monday afternoon.

The GFS model lifts the H5 trough a bit farther north and has a more
amplified solution than the ECMWF, with the potential for a meso-
scale heavy snowfall band developing along an Abilene to Valley
Falls line, with a potential snowfall accumulation late Sunday
afternoon through early Monday afternoon of 5 to 9 inches along
the Abilene to Valley Falls line and lower snow accumulations the
farther north and south of the heavy snowfall axis. If the GFS
solution were to verify, most of the accumulating snowfall will be
north of I-35. There would also be a potential for light freezing
drizzle Sunday night into early Monday morning across the extreme
southeast counties of the CWA, if the GFS solution were to
verify.

Sunday night a surface low will deepen across western AR and create
a tighter surface pressure gradient across eastern KS. Therefore
northeast-north surface winds will increase to 15 to 20 MPH with
higher gusts through the night into Monday morning. This may cause
considerable blowing and drifting of the snow. AS the upper trough
shifts east into MO Monday afternoon the snow will diminish and end
from west to east across the CWA during the afternoon hours of Monday.
North winds will be 10 to 20 MPH with higher gusts which may
cause some continue blowing and drifting of snow especially during
the morning hours of Monday.

Stay tuned to the latest forecast for accumulating snowfall Sunday
afternoon through Monday afternoon. The more finer grid resolution
models will begin to extend into the Sunday-Monday time frame in the
next couple of forecast shifts.

Monday night through Thursday, A longer wave-length upper trough
will develop across the eastern US. the central and southern Plains
will be in the northwest flow aloft pattern. Expect dry and cold
conditions to continue through mid week with highs in the 30s and
lows in the teens. The lows Tuesday and Wednesday night may dip into
the single digits if we have snow cover across much of the CWA. We
may see a slight warm up into the upper 30s to lower 40s by Thursday
as the cold surface ridge shifts east into the mid MS River
Valley.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1135 PM CST Thu Dec 12 2019

With fairly clear skies and light winds, the potential for ground
fog has increased. The terminals appear to be along the weakest
pressure gradient across the area through the night and may be
along the more favored fog swath. High clouds look to be
increasing again toward 12Z, but have enough concern to include
some limitations around 11Z.

&&

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

$$

SHORT TERM...Reese
LONG TERM...Gargan
AVIATION...65


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