Area Forecast Discussion
Issued by NWS Topeka, KS

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652
FXUS63 KTOP 172324
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
524 PM CST Wed Jan 17 2018

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Thursday)
Issued at 220 PM CST Wed Jan 17 2018

Little in the way of sensible weather is forecast for tonight and
tomorrow with warmer weather on the way.

Surface high pressure currently centered over the Ark-La-Tex
region will gradually sink southward tonight and tomorrow. Return
southwesterly flow has set in across NE Kansas, but this weak WAA
has been overpowered by the current snowpack. Therefore, have
trended temperatures lower for the period since much of the energy
in tomorrow`s airmass will go into melting the snowpack. Expect
that temperatures in north central Kansas, where little to no snow
exists based on visible satellite imagery, will reach the upper
40s to low 50s. However, to the east, areas with a snowpack depth
ranging from 1-4 inches or downstream of the snowpack will see
their temperatures modulated down into the upper 30s to around 40
(especially given that the dewpoints will only been in the teens
and 20s). The extent of the modulation is the biggest challenge of
this forecast package as it could mean a 10+ degree swing in
temperatures.

.LONG TERM...(Thursday night through Wednesday)
Issued at 220 PM CST Wed Jan 17 2018

Warm weather will be the theme for Friday through Sunday, with
the next chance of precipitation coming on Sunday/Sunday night.

The Central Plains will remain in split upper tropospheric flow
for the end of the work week with southwesterly boundary layer
flow pumping warm air northward. Highs on Friday will depend on
how much snow remains on the ground--there are indications in the
various guidance solutions that currently forecast highs for
Friday are too warm. Will wait to assess Thursday`s snow melt
before making major adjustments to the temperature forecast. Winds
on Friday will increase to 10 to 20 kts, which should aid in
reducing the effects of the snowpack on temperatures.

Overall, have made minimal changes to the forecast for the
weekend system. An H300 trough digs southward over California
early Saturday and ejects into the Four Corners region by 06Z
Sunday, possibly transitioning to a cutoff low as it lifts over
the Central Plains late on Sunday. Medium range solutions are in
good agreement on the general evolution of the upper level wave
with some expected timing discrepancies. The lee surface cyclone
pulls off the Front Range around 06Z Sunday with increasing
baroclinicity along a warm front arching eastward into Kansas. The
deepening 999 mb surface cyclone looks to lift through NE Kansas
Sunday afternoon with much of the area under the influence of the
dry slot Sunday evening. With 200-400 J/kg of MLCAPE and 50-60
kts of deep shear, the potential exists for organized upright
convection in the warm sector Sunday afternoon across far east
central Kansas and have added the mention of thunder with this
forecast update. The trailing deformation zone will primarily
impact locations north of the forecast area, but will slide
across NE Kansas Sunday night and bring with it some snow.
Amounts over much of the area looks to be light. The exception may
be far NW portions of the CWA, but there is a modest degree of
uncertainty on the placement of this band. CAA behind this system
early next week looks to be limited given the zonal flow pattern
developing in its wake.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 520 PM CST Wed Jan 17 2018

VFR conditions are expected through the TAF period. Southerly
winds will remain near 10kts through much of the period. LLWS
around 20-25kts is expected overnight as a 35kt LLJ positions near
1kft. Did not mention in this TAF issuance as the threshold is
30kts.

&&

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

$$

SHORT TERM...Skow
LONG TERM...Skow
AVIATION...Baerg



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