Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 201129
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
529 AM CST Tue Feb 20 2018

...AVIATION UPDATE...

.SHORT TERM...(Today and tonight)
Issued at 412 AM CST Tue Feb 20 2018

09Z water vapor imagery shows a longwave trough over the western
U.S. with a fast southwesterly flow over the central plains. At the
surface, a cold front has pushed into west central MO and southeast
KS with all but Anderson County below freezing.

The primary concern this morning is with the NAM and convective
allowing high resolution models developing another round of
convection that spreads across east central KS through the morning.
With temps already near or below freezing, the potential for ice
accumulations greater than a quarter of an inch is a little higher.
And I do not expect temps to warm at all across east central KS.
It`s hard to find an obvious wave supporting convection this
morning. Nevertheless an area of convection is already forming
across northwest OK. Another consideration will be the winds. By
late morning they are expected to pick up to around 15 MPH which
could cause more problems with ice covered tree limbs. With
everything pointing to a few hours of moderate rain with freezing
temps, will upgrade parts of east central KS to a warning for ice
accumulations around a third of an inch. With north winds picking
up, there could be some power outage issues as well.

Aside from the convection, the forecast continues to show precip
chances diminishing through the day as the surface ridge steadily
moves south. All indications are for the isentropic upglide to
end shortly this morning. Dry air with the surface ridge should
push all of the precip out of the area by 00Z. Temps are not going
to warm much today. However models do scatter out the low stratus
during the afternoon. So some insolation may help temps warm a
degree or two in the afternoon in spite of the continued low level
cold air advection. For tonight the surface ride remains over the
area with cold air advection persisting. However the NAM and GFS
show some mid level clouds moving back over late tonight. This may
keep temps from bottoming out and have lows in the teens.

.LONG TERM...(Wednesday through Monday)
Issued at 412 AM CST Tue Feb 20 2018

The active weather pattern looks to continue into the extended
period with freezing rain and/or drizzle potential Wednesday night
and again Thursday night. Another round of wintry weather is
possible Friday night into Saturday as well.

Wednesday through Thursday: The main mid-level trough will remain
positioned across the Inner Mountain West region. Surface high
pressure across the northern Plains is progged to slowly shift
eastward into the upper midwest by Wednesday evening. As a result,
the Canadian air mass will remain in place across northeast KS
through at least Thursday. The potential for wintry precipitation
looks to increase after 00Z Thursday as a weak, lead shortwave
trough ejects across the central Plains. In response to the mid-
level shortwave, WAA is progged to overspread the region with the
maximum moisture transport near H85. Ahead of the lead shortwave
trough, sufficient moisture exists within the H5 to H7 layer for ice
nucleation. Warm nose temperatures are progged to greatly vary from
NW to SE across the CWA. All solutions are consistent with the
placement of warm nose temps >0 being along and southeast of I-35.
That being said, the magnitudes vary amongst guidance.
GFS/ECMWF/Canadian solutions have max warm nose temps near +2C
through 06Z Thursday, while the NAM approaches +5C. For this reason
have a mention of snow and sleet for areas along and southeast of I-
35 and all snow for areas northwest of I-35 through 06Z. As the
aforementioned lead shortwave trough pushes northeast of area, much
drier mid-level is progged to advect across the CWA, ending ice
nucleation within the column. Albeit varying magnitudes of ascent,
all solutions suggest some measure of isentropic upglide within the
280K to 295K layer overspreading the CWA after 06Z Thursday. As a
result, expected freezing rain and/or freezing drizzle to overspread
the CWA. With no air mass change expected over the next 48 hours,
expect any freezing rain/drizzle to create slick conditions,
especially elevated surfaces. Solutions weaken isentropic upglide
after 12Z Thursday, as a result expected the coverage of drizzle and
rain to greatly decrease. The aforementioned surface high pressure
is progged to eject into the northeastern CONUS, allowing a
southerly component of the surface winds to return to the CWA. As a
result surface temperatures are progged to rise above freezing
Thursday afternoon, transitioning any lingering precipitation to all
liquid.

Thursday Night - Friday: The synoptic scenario is very similar for
Thursday night in comparison to Wednesday night. The major
difference being surface temperatures, given the WAA expected
Thursday afternoon. A weak, mid-level shortwave trough will once
again overspread the central Plains Thursday evening into Thursday
night. Again, varying magnitudes but all solutions suggest
isentropic upglide within the 280K to 295K layer will overspread the
southeastern 1/3 of the CWA after 00Z Friday. Portions of eastern KS
look to reside within the right-entrance region of a H3 speed max.
Thermal profiles would suggest a predominately all liquid rain
solution, with any freezing potential confined to north central KS.
The isentropic upglide is progged to shift into MO through the
morning hours Friday, shifting precip chances east of the area by
dawn Friday morning.

Beyond Friday, model solutions diverge on the evolution of the main
mid-level trough. ECMWF/Canadian solutions greatly shear the trough
upon entering the central Plains, while the GFS traverses a
negatively titled trough across the CWA. Bottom line, the potential
exists for another round of wintry precipitation Friday night into
Saturday. Southerly surface flow looks to return to the CWA by
Sunday, allowing temperatures to reach the 50s Sunday and Monday
afternoons.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 529 AM CST Tue Feb 20 2018

The HRRR and other high res models show showers and thunderstorms
moving back into TOP and FOE this morning while staying just east
of MHK. Think the IFR conditions will persist at TOP and FOE until
the precip passes east. Overall, improving conditions are expected
through the day as a surface high builds into the area with dry
low level air moving in.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon CST today for KSZ009>012-
020>024-026-034>039-054.

Ice Storm Warning until 3 PM CST this afternoon for KSZ040-055-
056-058-059.

&&

$$

SHORT TERM...Wolters
LONG TERM...Baerg
AVIATION...Wolters



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