971 
FXUS63 KTOP 201738
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1138 AM CST Tue Feb 20 2018

...Update to aviation forecast discussion...

.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 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1135 AM CST Tue Feb 20 2018

For the 18z TAFs, areas of freezing rain from earlier this
morning have shifted east of the TAF sites, but MVFR cigs will
continue to linger through mid-afternoon before scattering out to
VFR conditions for the remainder of the TAF period. Northerly
wind gusts near 20kts will continue through this afternoon and
even into the evening before gradually diminishing before sunrise
Wednesday morning.  

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Ice Storm Warning until 3 PM CST this afternoon for KSZ040-
054>056-058-059.

Winter Weather Advisory until noon CST today for KSZ022-026-
035>039.

&&

$$

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