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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

FXUS63 KTOP 170835

Area Forecast Discussion
National Weather Service Topeka KS
335 AM CDT Wed Apr 17 2019

.SHORT TERM...(Today and tonight)
Issued at 335 AM CDT Wed Apr 17 2019

A storm system and associated cold front will move through the area 
today and will bring a chance for thunderstorms, some of which could 
reach severe limits. Main severe weather threats look to be large 
hail, damaging wind and potentially heavy rainfall.

As of 08Z this morning, a surface low was located in western KS with 
a warm front extending northeastward into south-central NE. 
Northeast KS was located in the warm sector of the system. A deck of 
stratus clouds had developed overnight as moisture continued to 
stream northward into the area within the warm sector. It is looking 
likely that mainly cloudy conditions will hold over much of the 
region today, with maybe some slight mixing out of the low stratus 
as heating commences. Temperatures should manage to warm into the 
upper 70s to near 80 degrees in most locations with some assistance 
of pre-frontal compression ahead of an approaching cold front.

The aforementioned cold front is expected to move into north-central 
KS by mid-morning and progress eastward reaching KMHK by around 
19/20Z and KTOP by approximately 22/23Z. CAPE will increase near and 
ahead of the front with limited CIN over the region this afternoon. 
Bulk shear in the 0-6km layer and potential energy should combine to 
allow for some strong storms to develop along the front, especially 
across east-central KS where timing of the front and favorable 
dynamics combine to create the most likely area for severe weather. 
Storm initiation is expected to be between 21Z and 00Z south of a 
line from Hiawatha to Manhattan to Abilene. Large hail and damaging 
wind gusts with the stronger storms still appear to be the primary 
hazards, however, there is at least a slight chance for a few 
tornadoes given the shear parameters. Heavy rain is also likely 
under thunderstorms with some training possible across the far 
southeastern CWA late this evening, so will have to monitor for 
localized flooding threat. 

The cold front should clear the entire area by 06Z with some light 
rain possibly lingering just behind the front into early Thursday 
morning. CAA will bring cooler lows to the area early Thursday with 
temperatures dropping into the 40s.

.LONG TERM...(Thursday through Tuesday)
Issued at 335 AM CDT Wed Apr 17 2019

Have some small POPs in the forecast for Thursday afternoon across
the western two thirds of the forecast area. Models have been
consistent in showing a signal for some diurnally driven showers 
developing on the back side of the upper trough. Forecast 
soundings develop pretty steep low level lapse rates with the 
potential for a couple hundred J/kg of CAPE. So there even could 
be some thunder Thursday afternoon. Think that this activity will 
fall apart by the early evening as boundary layer cooling removes 
the weak instability. 

Upper level ridging is progged to keep dry weather over the area
for Friday and Saturday. Temps should Begin to moderate as well 
with a southerly return flow developing by Saturday. Models show 
decent low level warm air advection with 925MB temps warming to 
around 22C across north central KS. This would support highs on 
Saturday in the upper 70s and lower 80s, warmer than most of the 
raw model output. So have trended a little warmer than guidance. 

A weak southern stream wave with a frontal boundary is progged to
move through the central plains on Sunday and Sunday night.
Because of this have some chance POPs in the forecast. However
confidence in the models begins to lessen for Monday and Tuesday
as the GFS has had some run to run consistency issues. The ECMWF
and Canadian tend to be more progressive with the overall pattern
showing weak high pressure over the area by Monday. But the 00Z GFS
is more amplified with an upper trough over the southwest through
Tuesday. As a result it hangs up an inverted surface trough over 
the forecast area with southwesterly flow aloft and some potential
for precip on Monday and Tuesday. Since there is no clear trend 
in the model solutions, have gone with a blend with the forecast. 
This keeps some POPs in the forecast for Monday and Tuesday with 
more seasonable temps. 


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1119 PM CDT Tue Apr 16 2019

MVFR stratus looks more likely overnight and early this morning as
moisture has continued to be drawn north from southern KS/OK
vicinity. This should allow for the current MVFR to thicken up and
lower to below 3kft. Thinking only as low as around 2kft for now.
This should break up into the mid morning and at least lift to
VFR. The cold front advances into the area by the mid to late
afternoon hours. Uncertain on exactly where thunderstorms will
fire up. But, it looks like the focus area may be from central KS
into east central areas. This would likely keep more of a chance
for showers back into the KMHK area with a better scenario for TS
near the KTOP/KFOE terminals. Thus, have mentioned VCTS through
these sites. Winds veer to the northwest as the front advances
through and thus have maintained some gusts with colder and drier
air moving into during the evening on Wednesday into the overnight




LONG TERM...Wolters