Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 130522

Area Forecast Discussion
National Weather Service Topeka KS
1122 PM CST Fri Jan 12 2018

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Saturday)
Issued at 347 PM CST Fri Jan 12 2018

Northwest flow continues aloft over the central and western CONUS
behind Thursday`s upper wave. Water vapor and IR imagery show a weak
wave moving into the central Plains today with sporadic light
radar returns and some trace to very light measured precipitation
in snowfall from northwest Kansas into northeast Nebraska. A
stronger and more persistent area was just west of the CWA at 20Z
though ceiling heights remain above 6000 ft AGL and northeast
winds under this layer behind the surface ridge along the Missouri
River will continue dry air entrainment into this area into the
early evening. NAM, GFS, and ECMWF are consistent with weak mid-
level frontogenesis weakening this evening and the RAP and HRRR
have been consistent in diminishing precip trends over the next
several hours, and a small PoP for measurable amounts should

Weak low-level cold air advection continues through tonight, with
cloud cover with the weak wave slowly decreasing into midday
Saturday. With cloud cover persisting, have lows a touch warmer than
previous forecast, but single digits still expected with apparent
temps a few to several degrees below zero. Weak warm-air advection
develops Saturday afternoon, though the surface ridge remains to the
northeast for another cold day. Mid cloud returns in the afternoon
as a weak PV anomaly surges south out of western Canada.

.LONG TERM...(Saturday night through Friday)
Issued at 347 PM CST Fri Jan 12 2018

Models to differ with the speed and placement of the
aforementioned wave, but decent precip chances develop overnight
into Sunday morning as a narrow band of saturation moves through.
Lapse rates do increase and could support a few hours of light to
moderate snow with 1-2" snowfall potential as the column should
remain well below freezing for any mixed precip. This wave exits
by early Sunday evening, but attention will turn not far to the
northwest as a stronger wave comes south-southeast out of the
northern Plains with a potent cold front following. Another
narrow-in-time precip window moves across the area late Sunday
night into midday Monday as strong frontogenesis works through.
There are some differences in specifics at this range too, and a
stronger west wind around 850mb may be able to bring some mixed
precip in at precip onset as well as afternoon temps reach into
the 30s, but slightly higher precip/snowfall amounts seem in order
for this wave. Monday will likely be another day of early day
highs with temps falling into the single digits around sunset and
north-northwest winds continuing and Advisory- level wind chills
a good possibility from early Monday evening into midday Tuesday.

Conditions looking much less concerning for Wednesday into Friday as
the upper flow pattern shifts east and west to southwest flow
developing. There could be a shortwave passage around Thursday
though available moisture would likely be limited. South to
southwest surface winds may push temps to above normal levels next


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1117 PM CST Fri Jan 12 2018

VFR conditions are expected through most of the taf period. Winds
will weaken and gradually veer today as a surface ridge slides
through the area. By the end of the period the wind direction
should be southeasterly. An approaching mid-level system brings
the chance for light snow at MHK towards the end of the period. As
a result the ceilings could lower to near MVFR by 06z as
saturation works to the surface and snow begins.




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