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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

FXUS63 KTOP 221204

Area Forecast Discussion
National Weather Service Topeka KS
604 AM CST Fri Feb 22 2019

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 349 AM CST Fri Feb 22 2019

The short-term forecast period will mark the transition for yet 
another round of winter weather across much of the region with mix 
of spring-like weather as well (i.e. rain possibly enhanced with 
some instability aloft).  

Currently, the upper air pattern remains in place from previous 
periods with little change.  A deep semi-permanent long wave trough 
remains over the western CONUS with southwesterly flow over the 
region.  At the surface -- and lowest levels above the surface -- 
moisture has remained largely settled off to the south of the area. 
This has helped keep the area clear of clouds overnight thus far. 
There is at least some evidence that low stratus is beginning to 
develop over southern and southeastern KS as general broad scale 
ascent is slowly on the rise and moisture is showing some signs of 
beginning to return within the 925-700mb layer per mesoanalysis data 
and hinted at by some upstream 00Z obs (albeit shallow and meager). 
Meanwhile, another area of mid level moisture and subtle shortwave 
was working through western and KS into western and central NE. Some 
observing sites in NE were reported light snow while most reports in 
western KS were mist with upslope flow in place.  

For our area, the main forecast challenge remains when any 
precipition will commence across the area today.  A lead wave should 
work over the region later today.  This will aid in further ascent 
and further enhance isentropic ascent along the 295K surface into 
later this afternoon and overnight period.  Temperatures at the 
surface warm steadily today and a deep warm nose works into the area 
as well.  Thinking that this will allow for all liquid rain and 
drizzle over much of the area -- with some of the rain rates 
potentially convectively enhanced. One challenge with this will 
be along the Hwy 36 corridor as WAA is slower to win the 
temperature battle today. This may actually cause a situation 
where light freezing drizzle or rain could be supported late 
afternoon or perhaps overnight. Due to the depth of the warm nose 
and surface wet-bulb temps mainly forecast to be just above 
freezing, have to low confidence to issue an advisory. If 
traveling along the Hwy 36 corridor this afternoon or evening 
though, one should be prepared for the possibility of a very light
glaze of ice especially on untreated surfaces. This situation is 
literally a degree or two away from one type of precipitation or 
the other. So, it may be possible that a short-fuse advisory has 
to be considered later today before the next period which will 
contain the bulk of the winter weather arrives into Saturday. 

.LONG TERM...(Saturday through Thursday)
Issued at 349 AM CST Fri Feb 22 2019

Winter weather is still on tap for Saturday spreading from west to 
east across the north central and northeast Kansas through the day. 
Models continue to cluster around a common track for the upper low 
progressing out of the southern Rockies and across Kansas on 
Saturday and went with a blend of the ECMWF,CMC and the NAM. The gfs 
is displaced further to the northwest and was not preferred to the 
above mentioned models. Widespread forcing will overspread the 
forecast area on Saturday with rain predominately expected through 
the morning hours then as the upper low tracks northeast through the 
afternoon a surface low is expected to move from the Oklahoma 
panhandle northeast across south central and east central Kansas in 
the afternoon then move off into Missouri by early evening. The left 
exit region of the upper jet along with diffluent flow aloft in the 
mid levels and increasing moisture advection will enhance 
precipitation efficiency through the day. Problem of the day will be 
two fold with the first being potential flooding resulting from 
runoff due to saturated ground. The second is the transition to snow 
and blowing snow. As the surface low moves northeast into east 
central Kansas and into Missouri strong winds are expected on the 
backside across north central and northeast Kansas. The may cause 
near blizzard or blizzard conditions in the mid afternoon through 
the evening hours. Will continue with the winter storm watch at this 
time as adjustments in storm track may alter the timing and the 
area. I have adjusted the start time to noon for parts of north 
central Kansas with northeast Kansas starting after 2 PM. Potential 
loss of cloud ice in the evening may lead to areas of freezing 
drizzle along with the snow, but amount of ice will be less than a 
tenth of an inch. Current snowfall amounts of 3 to 5 inches expected 
across north central Kansas with lesser amounts elsewhere. 

Looking ahead from Sunday into Tuesday dry weather is expected with 
a west northwest flow and the jet retreating northward to the 
Canadian border as a ridge builds across the west. There is the 
potential for a small chance of precipitation on Wednesday as a 
minor mid level wave moves through in the northwest flow.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 519 AM CST Fri Feb 22 2019

Trends have continued to delay developing drizzle and rain over
the area today. There is generally good confidence that when
precipitation does develop that CIG/VIS conditions will
deteriorate through the period. Right now have gone as low as IFR
at most locations and could realistically expect lower. But, do
expect that precipitation will be fairly steady for a longer
period of time before leading into the main system during
subsequent periods. 


Winter Storm Watch from Saturday afternoon through Saturday 
evening for KSZ008-009-020-021-034.

Winter Storm Watch from Saturday afternoon through Saturday 
evening for KSZ010>012-022>024-035>038.