Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 180951
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
351 AM CST Sun Feb 18 2018

.SHORT TERM...(Today and tonight)
Issued at 351 AM CST Sun Feb 18 2018

Very strong winds will be the biggest impactful weather today,
with increasing clouds and a chance for precipitation tonight.

Kansas will find itself in broad WSW flow today and tonight as a
high amplitude upper tropospheric trough digs across the Pacific NW.
Height falls ahead of the trough allows a lee cyclone to pull off
the Front Range later today and be rapidly shift across Kansas
tonight. The attendant cold front bifurcates the NW third of the CWA
by 12Z Monday. Nudged high temperatures today a few degrees warmer
than yesterday with H850 temps likewise a few degrees higher, but NE
Kansas looks to miss out on tapping into a +15 C H850 downslope air
mass, which arrives after 00Z tonight. Widespread high clouds also
throw some degree of uncertainty on how high temperatures today will
climb. Lows tonight will vary greatly between the upper 20s in north
central Kansas to the low 50s in the warm sector from Manhattan on
east.

However, winds will be the main story of the day with a tight 20 to
40 ubar/km pressure gradient setting up over the state. A 50 to 80
kt LLJ has developed early this morning as evident on the KEUX VAD
wind profile, which as of 09Z has 70 kt winds between 925 and 850
mb. Both the HRRR and RAP have be consistently showing these winds
mixing to the surface between 14 and 15Z this morning, with the HRRR
in particular pushing 40 to 50 kt wind gusts between 15 and 18Z from
the Flint Hills on west. While the effects of the LLJ wane by
midday, advisory level sustained winds are expected through the
afternoon, only lessening slightly overnight. A wind advisory has
been issued starting at 9am for all but the far eastern CWA with an
emphasis that the highest wind gusts may occur before noon.

The southerly winds will advect increasing moisture from the
Southern Plains today and tonight. The leading edge of this theta-e
advection surge was located in SE Kansas, where dewpoints at KCNU
have increased 13 degrees in the last five hours. Despite strong
mixing today, this influx of moisture keeps RH values from falling
too much this afternoon, if at all. Low stratus looks to move into
east central Kansas before sundown, spreading throughout NE Kansas
over the ensuing few hours. Various ensemble and deterministic
guidance have been generating light QPF (drizzle) under the stratus,
though the depth of the stratus and the lift through that layer in
the RAP/NAM soundings is not overly impressive. For this reason,
have not gone too bullish on POP coverage or amounts tonight.
Despite a modest H700 to H800 EML, the aforementioned H850 capping
inversion will make it very difficult to generate convection.
However, with a 70 kt LLJ just under the warm nose and the NAM
showing some weaknesses in the elevated inhibition fields with 400-
700 J/kg of MUCAPE, kept a slight chance of showers/thunderstorms
mentioned E/SE of the Turnpike after 06Z tonight.

.LONG TERM...(Monday through Saturday)
Issued at 351 AM CST Sun Feb 18 2018

An active weather pattern is shaping up for the work week. The
biggest concern comes on Monday night and Tuesday as models point
towards an freezing rain event with the potential for more than
just minor ice accumulations. Forecast soundings show cold air
pushing south through the period as warm air in mid levels
remains. Even if there is ice in the top of the cloud, model progs
of the warm nose well above +3C would support complete melting
and then precip falling into sub-zero temps at the surface. The
biggest uncertainty is how quickly the cold air at the surface
pushes southeast. The GFS has trended much slower with the advance
of the cold air while the NAM blasts it through the area fairly
quickly. The ECMWF and Canadian solutions tend to be somewhere in
between and it is this compromise on the thermal profile that was
used for the forecast. In general, all the models are showing a
surge in moisture late Monday night into Tuesday morning.
Shortwave energy remains rather subtle within the southwest flow
aloft, but there are indications of some frontogenesis and even
some convective instability along the boundary Tuesday morning as
the moisture surge occurs. So the general trend for increasing QPF
amounts seems plausible. I think there will be a narrow band
where conditions for ice accumulations will be good given the cold
air from the north and the moisture moving up from the south. At
this point confidence in the location of this band is low due to
the poor agreement among the models on the speed of the cold air
moving south. Although confidence in freezing rain occurring is
high. Based on the preferred ECMWF/Canadian thermal solutions, the
higher ice accumulations may be along an axis from Herington to
Hiawatha. For now those accumulations are forecast to be on the
order of 1 to 2 tenths. However if the cold air surge is more in
line with the NAM and makes it deeper into east central KS where
the heavier QPF is expected, ice accumulations could be more
significant. Temps are expected to remain nearly steady or fall
both on Monday and Tuesday with little insolation and continued
cold air advection. By Tuesday night, the cold and dry air moving
south is expected to win out with precip chances moving southeast
of the forecast area. Clearing skies Tuesday night could allow
temps to fall into the single digits and teens by Wednesday
morning.

For Wednesday through Saturday, there is quite a bit of uncertainty
in the forecast as models have shown poor run to run consistency.
Southwest flow aloft is progged to persist while energy digs into
the southwest and reinforces the upper trough late in the work week.
Models hint at some warm air advection precip anytime from Wednesday
afternoon through Thursday. Although none of them agree on the
timing or location of the precip. Eventually energy from the
southwest gets kicked out and brings a surface wave through the
central plains. Again timing issues persist with the GFS lifting the
system into the Great Lakes by Saturday while the ECMWF and Canadian
are about 24 hours slower with the upper energy and surface low. So
the consensus forecast has some POPs for rain and snow in just about
every period from Wednesday through Saturday. Expect this forecast
to change as the model solutions hopefully converge towards a common
idea. Temps are expected to moderate as the surface ridge over the
area on Wednesday weakens and moves east. Highs are forecast to be
in the 40s and 50s by the end of the period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1118 PM CST Sat Feb 17 2018

Low level wind shear is expect this morning with a strong low
level jet developing over central KS and spreading eastward. With
a modest jet in place occasional gusts may make it down to the
surface overnight although this could be limited since it appears
the nocturnal inversion seems rather strong. The surface gusts
may rapidly increase with the onset of day time mixing a few hours
after sunrise. Towards the end of the period possible MVFR
stratus moves towards the sites from the south.

&&

.FIRE WEATHER...
Issued at 351 AM CST Sun Feb 18 2018

Southerly winds of 25 to 35 mph with gusts of to 35 to 50 mph are
expected today, with the strongest winds likely between 9am and
noon. Warm temperatures will lead to daytime RH values falling to
between 30 and 40 percent, but increasing moisture from the south
will boost dewpoints as the afternoon progresses. This increase in
moisture keeps fire weather conditions below extreme levels, but
nevertheless the very strong winds will make fire control very
difficult. Outdoor burning is strongly discouraged.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 9 AM this morning to 6 PM CST this evening
for KSZ008>012-020>024-034>039-054-055-058.

&&

$$

SHORT TERM...Skow
LONG TERM...Wolters
AVIATION...Sanders
FIRE WEATHER...Skow



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