Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 100534

Area Forecast Discussion
National Weather Service Topeka KS
1134 PM CST Tue Jan 9 2018

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Wednesday)
Issued at 345 PM CST Tue Jan 9 2018

Skies were clearing in the wake of the mid level wave that passed
across eastern Kansas. Temperatures have warmed into the 40s and 50s
across the cwa. Tonight the surface trough across the High Plains
will continue to deepen increasing the pressure gradient through the
night. Forecast soundings suggest that the lower boundary layer
will remain mixed through the night in the warm air advection
pattern. Also NAM, RAP, and GFS soundings suggest increasing lower
level moisture forming a stratus deck later this evening and
overnight across northeast and east central Kansas and have
increased clouds late this evening and overnight. Lows tonight will
cool into the mid and upper 30s.

On Wednesday, the surface low will deepen and move into southeast
Colorado or southwest Kansas by late afternoon. Warm advection will
continue across the area in the broad warm sector. Temperatures
should warm into the 50s to near 60 across the cwa in the afternoon.
The Upper trough will move across the southern Rockies and into west
texas by 00Z Thursday. Some light drizzle may develop late in the
afternoon across north central Kansas. NAM looks overdone with the
low level moisture across the area and was discounted.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 345 PM CST Tue Jan 9 2018

Highlight of the mid-range forecast period continues to be potential
for snow and mixed precip overnight Wednesday into Thursday morning
and to a lesser extent light snow chances again overnight Friday
into Saturday morning coming in the longer range period.

Closed mid level low continues to dig and deepen as it translates
into the Central and Southern Rockies.  Meanwhile another piece of
the split northern stream energy will begin to phase with this
system as it lifts into the central Plains by Wednesday night
essentially very quickly takes on a negative tilt and therefore
evolves quickly during the overnight period.  As the system and
associated PV anomaly lifts into the region, the upper low also
transitions to an open wave.  There is still some slight discrepancy
over exact positioning of the TROWAL feature and low to mid level
frontogenetical forcing band of snow with the deformation zone.  GFS
has the most robust band of snow along with the Canadian which focus
heaviest amounts over north central KS.  ECMWF and NAM develop a
more broad area of somewhat lighter precip amounts but in the same
general area overall and generally colder solutions. Looking for
snow amounts in the end all told by 18Z on Thursday to be in the
neighborhood of 1-2 inches in far northwestern counties in the
forecast area and along the KS/NE border. It is possible to have
some locally heavier amounts, but generally this should be focused
more into NE with the better TROWAL region set-up. Mixed precip
will be the bigger concern likely into the midnight and after time
frame for the forecast area before the northwest to southeast
transition of snow takes place as colder air is funneled into the
region with strong gusty winds wrapping with sustained winds of
20-25 mph with gusts up to 35-40 mph into Thursday morning. With
warm temps from Wednesday transitioning to below freezing during
the period this system moves through Wednesday night into
Thursday, snow ratios are probably lower which helps produce
overall lower amounts of snow in the end. But, the rain/drizzle to
freezing rain/drizzle will be a concern over areas too.
Therefore, do anticipate some type of advisory will likely be
needed. However, have held off for the overnight period tonight to
better determine exact areas that will be most impacted. Would
ultimately like to get a better handle on how this transition
takes place and potential placement of the dry slot aloft to
better determine which areas to put under any advisory. Also, have
kept with the idea of some blowing snow with the strong winds
behind the system, but have limited this area to most likely
impacted areas seeing snowfall. Expected time frame for freezing
impacts via ice accumulations will be during the midnight to 6am
time frame Thursday morning as well. But have kept only very light
glaze mentioned at this point due to concerns about overall QPF
amounts involved as well.

High temps again plummet into the teens by teens by Saturday.  Wind
chills again near the advisory level Saturday morning. Weaker wave
dives down for overnight Friday into early Saturday as well, but
only light snow amounts likely focused over far northeastern KS
with this quick hitter.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1130 PM CST Tue Jan 9 2018

IFR stratus will persist past 12Z Wed east of MHK, gradually
dissipating around 15Z. MVFR ceilings look to redevelop area-wide
after 00Z Thu. Winds will remain from the south through the
period, increasing to 15 to 30 kts during the day on Wednesday.
Marginal LLWS will be possible for the rest of the night at all
TAF sites.




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