Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 110933

Area Forecast Discussion
National Weather Service Topeka KS
333 AM CST Wed Jan 11 2017

.SHORT TERM...(Today and tonight)
Issued at 329 AM CST Wed Jan 11 2017

Upper flow remains fast and zonal over central and nearby
sections of the CONUS with a low making more slow eastward
progress across Saskatchewan and Manitoba. Periods of cirrus
overhead, generally increasing in coverage overnight, and in
concert with a strong southwesterly low level jet, temperatures
have risen, with some hourly changes of near 10 degrees. Much
colder air with temps around 0 F was behind a cold front that was
entering northern Nebraska.

Temperatures are the main forecast challenge through tonight.
Southwest winds will continue to increase into the late morning
for southern areas but the front enters northern areas around this
time. Southeast locations look to have the strongest winds again,
but should remain below Advisory levels. The early afternoon hours
should bring a rather sharp temperature gradient across the area
with 30 F ranges likely. The NAM continues to struggle with too
much low level moisture, and suggests some possibility for drizzle
in stratus along the front in the late afternoon, but have little
confidence in this occurring. Shallow but strong cold air
advection weakens overnight as the zonal flow aloft remains. Given
aforementioned observed temps north of the front, have gone on the
low end of guidance lows.

.LONG TERM...(Thursday through Tuesday)
Issued at 329 AM CST Wed Jan 11 2017

Cold high pressure continues to drive southward across the Plains
states on Thursday, leaving north winds and highs only in the
middle 20s north to possible mid 30s south. Temps Thursday night
look to fall into the teens before cloud cover increases from the
south in the early morning hours. Through the day on Friday begins
the return flow aloft over the cold dome and warm nose, and by the
afternoon hours some models start some light precipitation which
would be light freezing drizzle/rain. QPF amounts are quite low,
but certain to freeze on contact and areas that do get light
precip will likely have light glaze afternoon into overnight. EC
dries out the area briefly on Saturday while the GFS keeps light
accumulations going in the southeast counties, then back north
across the area into the afternoon, but again amounts are light.

Of greater concern at this time in the forecast process continues
to be types and amounts of potential ice/sleet/rain for Saturday
night into Sunday and Sunday night. The 32 degree line continues
to play a critical role in this forecast and its position remains
elusive as it changes from model run to model run. Also counties
farther to the north and west cool enough in the warm nose to get
more sleet than freezing rain for portions of this forecast.

BY 0Z Sunday, the GFS starts to ramp up precip amounts and by 12z
had a quarter to half an inch over the SW half of the forecast
area...keeping areas along and south of I35 at or above freezing.
GFS gives the SE a break 12-18z but cranks out another half inch
of precip at or below freezing across the northern half of our
CWA, with another quarter inch in the west for the afternoon at
temps very close to or below freezing. So - increasing threat for
significant ice as you go north and west. Hopefully the above zero
surface temps from 0-6z Monday pan out, given the inch of precip
the GFS carries for that period.

The EC is more ominous with ice potential, given it keeps the
entire forecast area below freezing and under a warm nose from 0Z
Sunday through 0Z Monday, with QPF ranging from a quarter inch
near the NE border, up to around 1.5 inches in the far southeast,
with an inch centered along the I70 corridor. Current run brings
I35 and south counties above freezing at 06z Monday but leaves
north below...with another quarter inch northeast to nearly an
inch in the west counties that evening...and another half inch to
an inch north and west of I70 through 12z Monday. Thats 1-2 inches
of liquid before temperatures finally potentially rise above
freezing across the area on Monday afternoon. So - the threat for
significant ice is area-wide...with heightened concern out west if
the cold remains in place for this additional accumulation Monday.

Current EC lifts above freezing temps across all but the far NW
counties by late Monday afternoon, with this process slightly
faster in the GFS. Guidance gives highs in 40s for Tuesday as
well. So hopefully this will be a fast hitter before warming above
freezing. Again...given uncertainty in amounts...temperatures and
impacts...continue to monitor this situation and plan the weekend


.AVIATION...(For the 06Z TAFS through 06Z Thursday)
Issued at 1126 PM CST Tue Jan 10 2017

Not a lot of change to the forecast thinking as models continue to
show limited moisture in spite of some dynamic flow over the
forecast area. Therefore a VFR forecast is expected through
tonight and much of Wed. Profilers showing the low level jet is
intensifying so LLWS continues to appear likely with a steep
nocturnal inversion setting up. Models have shown some MVFR CIGS
developing behind the front late Wed and Wed evening with decent
low level cold air advection. With some consistency from the
models, have introduced a BKN MVFR CIG around 00Z Thursday.




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