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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

FXUS63 KTOP 171706 AAA

Area Forecast Discussion...UPDATED
National Weather Service Topeka KS
1106 AM CST Sun Feb 17 2019


.SHORT TERM...(Today and tonight)
Issued at 405 AM CST Sun Feb 17 2019

Quieter weather is on tap for today and tonight with continued 
below average temperatures.

A light mixture of freezing drizzle and snow comes to an end 
across eastern forecast area early this morning as forcing for 
ascent and deeper moisture shift to the east with a decaying PV 
lobe. A strengthening NW/SE-oriented ridge axis along the High 
Plains will increase the pressure gradient slightly and facilitate
weak lower-tropospheric CAA through the day. Steepening boundary-
layer lapse rates owing to this differential CAA could result in 
enough static stability reduction that convective temps are 
realized and a stratocumulus deck develops. Coupled with lingering
broad upper-level cyclonic flow, areas along and north of I-70 
could see some stray flurries during the afternoon hours from this
(albeit thin) cloud deck as depicted by the 00Z HREF. Winds at 
the top of the boundary-layer push 20 to 25 kts, which may also 
reach the surface as gusts during this peak mixing.

Clouds should mostly clear out around sunset with the surface 
high pressure axis lingering west of the forecast area overnight. 
Light northerly winds should prevent temperatures from plummeting 
too far, but could still see readings fall into the single digits 
to mid low teens, a solid 10+ degrees below average for this time 
of year.

.LONG TERM...(Monday through Saturday)
Issued at 405 AM CST Sun Feb 17 2019

Focus for the longer term forecast remains on Tuesday's weather 
system which could bring a few inches of snow to the area.

Broad upper-tropospheric cyclonic flow over the western two-
thirds of the CONUS amplifies on Monday/Monday night as upstream 
ridging builds along the Canadian west coast. Models have backed 
off on any potential snowfall on Monday attendant with a subtle 
H500 wave lifting through western Kansas ahead of the main system,
with increasing low to mid high cover being the main sensible 
weather impact. By early Tuesday morning, deep isentropic upglide 
increases along the 280-300K surfaces as H850 cyclogenesis takes 
place along the Front Range. While the strong upper-level 
kinematic support associated with this approaching wave and left-
front quadrant placement of the 140 kt jet will undoubtedly lead 
to a widespread swath of snow over the area, concerns rise over 
just how much snow will fall. 

With the main surface baroclinic zone located along the Gulf 
Coast, the incoming moisture influx ahead of the wave will undergo
significant modification before it reaches the Central Plains, 
and there is concerns that the models may not be fully taking this
convective modulation into account. Secondly, the lack of any 
mesoscale forcing will play a role in keeping snow amounts on the 
lower side. As with our system late last week, synoptic forcing 
alone will struggle to push snow rate much higher than 1/2" per 
hour for any substantial amount of time. Finally, there are 
signals that ice introduction may be lost towards the latter half 
of the event, especially towards central Kansas. All of these 
factors throw an aura of uncertainty over snowfall amounts. The 
strong and deep lift through the column (and the DGZ) should 
produce a widespread swath of 2 to 4 inches of snow, highest along
the Kansas/Nebraska border. This forecast falls in line with the 
median GEFS/SREF forecast plumes. A light glaze of ice is likely, 
especially along and south of I-70, where a dry punch will lead to
a changeover in p-type.

The entire system departs early Wednesday morning with a short-
lived reprieve from precipitation for late in the week as the 
western upper-level trough goes through a redevelopment phase. 
However, by Friday, the trough should be reestablished with the 
chances for rain/snow returning late Friday and through the 
weekend. Recent runs of the GFS/EC/CMC depict a strong 
extratropical low developing over the weekend as this wave lifts 
out, which could bring impactful weather to locations across the 
central CONUS. However, significant timing and placement 
differences exist this far out and we will need to watch this 
system closely over the upcoming days to assess its impacts on 

Temperatures should remain below average through most of the 
week, with some modest WAA noted ahead of next weekend's system.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1106 AM CST Sun Feb 17 2019

Models continue to show a stratocu deck developing by the late
afternoon. Looks to remain VFR. Bigger question is overnight as
the RAP and NAM are suggesting there could be some MVFR stratus 
move south after 06Z. Objective guidance doesn't really have 
lowing CIGS so will keep the forecast VFR for now and monitor 
later model runs.