Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 211715

Area Forecast Discussion
National Weather Service Topeka KS
1215 PM CDT Mon May 21 2018

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 332 AM CDT Mon May 21 2018

This morning a mid level trough was located over south central South
Dakota extending into far northern Kansas. This feature is forecast
to gradually move east into the upper Mississippi Valley by late
evening with shortwave ridging moving across north central and
northeast Kansas later tonight. Weak surface high extended from the
Dakotas into the southern Plains. Main focus for this morning will
be areas of fog into mid morning with visibilities around a mile or
less at times. Clouds will be slow to move out today especially in
northeast and east central Kansas where models suggest clearing will
not occur until mid to late afternoon hours and have leaned more
toward the slower GLAMP for cloud trends. Lingering clouds and
little mixing will keep temperatures a couple of degrees cooler than
previous forecast, but still in the 70s to lower 80s.

Tonight, model trends have been to decrease precipitation chances
across north central and northeast Kansas with only the GFS
developing some elevated showers and thunderstorms. Moisture
transport looks to focus to the west and north of the CWA tonight
with the deeper moisture. Energy ejecting out of the Rockies looks
to move northeast into western and north central Nebraska. Forecast
soundings show elevated instability rooted near 850 mb after 06Z
Tuesday. Isentropic lift in the 305K-315K layer suggest best chances
for convection will focus to the north in Nebraska where isentropic
omega is the best. Cannot rule out a brief shower or Thunderstorm
across the far north as the low level jet increases tonight so will
continue with a small precipitation chance after 06Z focused mainly
near the Nebraska border. Lows tonight will fall to the lower 60s.

.LONG TERM...(Tuesday through Sunday)
Issued at 332 AM CDT Mon May 21 2018

Transitioning into the extended period, the main takeaways reside
with scattered thunderstorm chances and summer-like warmth for the
holiday weekend.

By midday Tuesday all shower/thunderstorm activity is expected to be
well north of the CWA where more favorable isentropic surfaces and
theta-e advection exist. Midlevel ridge axis will build across the
central and northern Plains as a cutoff midlevel low weakens in the
southwestern CONUS. A weak embedded midlevel shortwave is progged to
eject into the high Plains Tuesday afternoon, yielding thunderstorm
development in the Panhandle region. Given the meager effective
shear expected, the potential for any upscale growth of an MCS is
low Tuesday night, therefore do not have great confidence for
rainfall in the western counties Wednesday morning. Midlevel ridge
axis will amplify throughout the day Wednesday as a northern stream
trough digs into the northeastern US. While large scale ascent looks
minimal Wednesday -- noted by midlevel height rises -- convective
temperatures near 90 F may be reached by late afternoon, yielding
isolated to scattered thunderstorms. Modest midlevel lapses rates
near 7 C/km will contribute to MLCAPE nearing 1500-2000 J/kg but
effective shear values of 20-30 kts will greatly temper any severe
potential. The remnant closed midlevel low is progged to eject
across the northern Plains as an open wave Thursday into Thursday
night, shunting a weak surface trough towards eastern KS. Open warm
sector thunderstorms will once again be possible Thursday afternoon,
although minimal effective shear should hinder severe potential.
Some signal exists for elevated thunderstorms north of the
stalled/slow moving frontal boundary Thursday night/Friday morning.
Current indications would keep the bulk of activity across NE. The
vast majority of eastern KS is expected to remain in the warm sector
Friday afternoon, with the potential for late afternoon
thunderstorms. One more day of thunderstorm potential exists
Saturday afternoon before the surface trough pushes east of the area
Saturday night. Midlevel ridging and concurrent surface ridge axis
will build into the central and northern Plains for the second half
of the holiday weekend, yielding sunny skies and light winds with
temperatures in the 80s to near 90!


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1215 PM CDT Mon May 21 2018

Clearing of low cloud nearing TOP and FOE from the west and trends
suggest VFR will occur/develop near 18Z. Southerly winds slowly
develop through this period, with enough increase above the
nocturnal inversion tonight to keep limiting BR from developing,
but this will be the main item to watch over the next 18 hours.




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