Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 110538
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1138 PM CST Wed Jan 10 2018

.UPDATE...
Issued at 814 PM CST Wed Jan 10 2018

A fast-moving, potentially high impact storm system still on
track to impact the region Thursday morning. CAM guidance as well
as the synoptic solutions are locking into a narrow SW to NE
oriented frontogenetically-driven band of snow developing between
11Z and 16Z between Clay Center and Topeka, with recent HRRR/RAP
runs trending slightly further east than the 18Z GFS/00Z NAM. For
this forecast update, have tried to hone in on this enhanced
mesoscale band by increasing QPF values along this axis, but there
remains a modest amount of uncertainty on snow amounts. Recent
QPF progs are downright unsettling with max values in this narrow
band of half to three quarters of an inch--which would easily
double the currently forecast snowfall totals. However, given the
relatively short duration of this snowfall, these amounts will be
very time sensitive and subject to large degrees of fluctuation.
As a result, have trended QPF and snow amounts higher and will
wait until the full suite of 00Z guidance is in before making the
final call on snow amounts.

Combined with the winds, the potential exists for a very narrow
corridor of near-blizzard to blizzard conditions Thu morning.
Given the mesoscale nature of the band, any products highlighting
this enhanced risk will likely have a very short-lead time.
Messaging should continue to be focused on dangerous travel
conditions throughout the region with the potential for a very
narrow corridor of heavy snow.

&&

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Thursday)
Issued at 303 PM CST Wed Jan 10 2018

Upper level trough was moving across the southern Rockies this
afternoon. Broad warm air advection with southerly flow ahead of the
system has sent temperatures back into the 50s to around 60 degrees
across the cwa this afternoon. Surface cold front was located across
South Dakota into eastern Wyoming. Temperatures behind the front
were in the single digits and teens.

For tonight, the models are in agreement with the upper trough
ejecting northeast with a negative tilt across overnight and Thursday
morning. Temperatures are expected to remain above freezing until
frontal passage from northwest to southeast across the cwa. Expect
the front to move into north central Kansas around midnight then
progress southeast to near Topeka to Emporia between 6 AM and 8 AM
then from Lawrence to Burlington or near I-35 between 7 AM and 9 AM.
Temperatures are expected to quickly fall below freezing with the
frontal passage. Initial rain will quickly transition to snow across
north central and northeast Kansas. The trend in the models has been
to shift the high precipitation to the southeast from earlier
forecast. Good frontogenetic forcing sets up from southeast of Abilene
through Manhattan and Frankfort in the 09Z-15Z time period. This
area also aligns with convective instability along with increasing
forcing for ascent with the ejection of the upper trough. This may
likely lead to a narrow band of higher snowfall amounts and have
expanded the Winter Weather Advisory southeast for snow from Brown
County southwest through Morris County.

Further southeast there is increasing potential for a period of
freezing rain/drizzle and snow. There may be some periods dry air in
the dendritic ice crystal growth zone which would lead to freezing
drizzle rather than snow from the Turnpike southeast where a light
glazing is expected Thursday morning. Have issued a winter weather
advisory Thursday morning mainly for a wintry mix of precipitation.
Strong pressure gradient behind the front will lead to winds gusting
to 30 to 40 mph which will lead to areas of blowing snow and reduced
visibilities. With temperatures quickly falling below freezing any
wet and untreated surfaces will quickly freeze and become slick.
Additionally wind chills will fall into the single digits above and
below zero during the afternoon hours across the entire cwa.

.LONG TERM...(Thursday night through Wednesday)
Issued at 303 PM CST Wed Jan 10 2018

A cold arctic high pressure will build southward out of Canada as
temperatures plummet back into the single digits Saturday morning.
Wind chills will range from 4 to 12 below zero Saturday morning. A
clipper system will bring a chance of light snow Friday afternoon
and Friday evening. The cold air will be entrenched across central
and eastern Kansas with temperatures remaining below freezing for
much of the next week. Another shortwave clipper system will bring
another chance of light snow Saturday night and Sunday. Another cold
front is forecast to move through the central Plains Sunday night
and Monday as a broad upper trough moves across the northern and
central Plains.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1129 PM CST Wed Jan 10 2018

Widespread rain with accompanying MVFR/IFR ceilings will
overspread the rest of the area shortly after 06Z tonight,
transitioning to snow from northwest to southeast over the course
of the morning. A narrow band of higher snowfall is expected
running NE to SW, possibly through MHK, where near blizzard
conditions may be possible for a short amount of time between 12
and 18Z. A mix of RA/SN/FZRA is possible towards TOP/FOE this
morning. This precip exits the area around 21Z. Gusty southerly
winds will quickly subside, but quickly veer to the northwest and
increase to 20 to 30 kts between 06 and 15Z today (earliest in
north central KS).


&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 3 AM to noon CST Thursday for
KSZ010>012-022>024-035>038.

Winter Weather Advisory from 6 AM to noon CST Thursday for
KSZ026-039-054-055.

Winter Weather Advisory until noon CST Thursday for KSZ008-009-
020-021-034.

Winter Weather Advisory from 8 AM to noon CST Thursday for
KSZ040-056-058-059.

&&

$$

UPDATE...Skow
SHORT TERM...53/Sanders
LONG TERM...Sanders/53
AVIATION...Skow



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