Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 281740
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1240 PM CDT Wed Jun 28 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 320 AM CDT Wed Jun 28 2017

At 08Z WV and IR imagery show an MCS continuing to move through
eastern NE into western IA.  Trailing along the southern side of
this system is an associated outflow that has sparked a line of
storms from Marysville area extending back into central KS. Some
pockets of stronger storms have been seen within this line, but
overall have stayed well below severe thresholds which is expected
as the night continues.  The MCS and associated mid level shortwave
will continue to move off to the east into the early morning hours.
Some indication this complex is transitioning into an MCV as it does
so. Showers and storms should come to and end through the morning
hours over northeastern KS and give way to clearing skies.

This sets up the afternoon Wednesday into the evening and overnight
period with some uncertainty on exactly how it will evolve weather
wise.  With the mid and upper level pattern still mostly zonal,
another minor shortwave is expected to arrive into the
evening/overnight hours on Wednesday.  Outflow boundary left behind
with the departing MCS feature should modify throughout the day with
strong WAA still in place.  This will help push the boundary back to
the north as most guidance suggests that synoptic boundary sharpens
tomorrow over southern IA into southeastern NE and extends back into
north central and northwestern KS.  As moisture pools along the
boundary and daytime heating takes place along with mid level lapse
rates increasing to 7-8 C/km throughout the day into the evening,
MLCAPE values should increase to 2000-3000 J/kg.  The cap throughout
the day remains the main question as to how long it may take to
degrade. Considering the low level flow being as strong as it will
be, can`t totally rule out a tornado threat if storms do get going,
but the better deep layer shear won`t develop until the wave
encroaches into the region during the overnight period.  So, while
the threat is there, it does appear minimal.  This is all
considering if storms do again break the cap and mature.  Guidance
does develop storms overnight ahead of the wave coming off the
foothills of the Rockies.  With LLJ veering into the northeastern KS
it looks like a better set up for overnight storms may actually come
into the very early hours of the morning and into the 12Z time
frame.   At this point, the main hazards will be large hail and
strong outflow dominate winds.  All in all, this should be an active
period with several storm chances especially the latter half of the
period.

.LONG TERM...(Thursday through Tuesday)
Issued at 320 AM CDT Wed Jun 28 2017

Thursday through Friday, An upper level trough will move east across
the central plains. Thursday morning there could be a cluster of
elevated thunderstorms moving along and north of I-70. The area of
thunderstorms will move east into MO by Noon. An outflow boundary
will slowly drift north across Brown and Nemaha counties during the
late afternoon hours. Forecast soundings show an EML over spreading
much of the CWA during the afternoon. Beside the outflow boundary
across far northeast KS and northwest MO the surface front will be
well west and northwest of the CWA across west central and northwest
KS. MLCAPE will increase to 3,000 to 4,000 J/KG during the afternoon
hours and 0-6 KM effective shear will be 30 to 40 KTS. But it looks
as if the CAP will not break during the afternoon hours. The only
place the CAP may break would be across the far northeast counties
of the CWA if the OFB remains in the vicinity and is a focus for
surface convergence to break the CAP. If so, then the potential
exist for supercell thunderstorms with large hail and damaging wind
gust being the the primary hazards. If the cap manages to break in
the warm sector during the afternoon hours then the environment
would support supercell thunderstorms which would produce large hail
and damaging outflow winds. Overall, the low-level shear looks weak,
0-1 KM SRH less than 100 J/KG. Thus any threat for tornadoes looks
to be very low. May be is a supercell were to interact with the
outflow boundary across the far northeast counties there could be a
baroclinic generation of horizontal vorticity that could be tilted
by a thunderstorm updraft, increasing the chance for an isolated
tornado but this will be more of a mesoscale forecast. Highs on
Thursday will warm into the upper 80s to lower 90s. Heat indicies
may reach near 100 degrees in some areas during the afternoon hours.

During the late afternoon and early evening hours of Thursday,
upslope flow across northeast CO and southwest NE will form
scattered severe thunderstorms that will congeal into an MCS/QLCS.
This MCS will propagate east-southeast along the higher theta e
airmass across central and eastern KS. If the 0-3 KM shear vectors
are perpendicular to the line of storms, then the outflow may be
balanced enough to keep a severe wind threat across the CWA during
the mid to late evening hours across north central KS, and then
after midnight across northeast and east central KS. Any embedded
supercell updrafts may produce isolated large hail within the line.
There may  be meso vortices forming on the north side of any local
rear inflow jets that could spawn a few brief but weak tornado. I
think north central KS has the better chance of meso vortices
tornadoes during the evening hours. There will probably be heavy
rainfall as the MCS propagates southeast across the CWA. The fast
motion of the MCS may prevent widespread flooding but localized
flooding is possible Thursday night.

Friday, there could be a few showers lingering behind the front
across the southeast counties. Skies should clear from northwest to
southeast as the surface front pushes southeast into OK and AR.
Highs will be slightly cooler with lower to mid 80s.

Saturday looks dry as a weak surface ridge of high pressure moves
southeast across eastern KS into southern MO. Highs will warm into
the mid to upper 80s.

Sunday through Monday night, both the GFS and ECMWF amplify an upper
level trough as it digs southeast across the central plains. There
may be periods of showers and thunderstorms late Sunday afternoon
through Monday night. Highs will be in the mid to upper 80s.

Tuesday, July 4th, Both the ECMWF and GFS model solutions show the
upper trough digging southeast into the lower MS river valley which
should cause any lingering showers during the day to move southeast
of the CWA during the evening hours. So, far any firework shows may
be in good shape for Tuesday evening. However the model solutions
could change over the next several days. Highs will be in the mid to
upper 80s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1236 PM CDT Wed Jun 28 2017

VFR conditions are expected through the afternoon and evening
hours. Southerly winds will remain sustained 15-25kts with gusts
upwards of 25-30+ kts through the early evening. Thunderstorms are
expected to develop late this afternoon, however they look to stay
north of the terminals. Another night of LLWS as the LLJ increases
to near 50kts. A complex of thunderstorms is expected to develop
across portions of western and central KS late this evening and
push eastward. Only mention VCTS at the terminals during the early
morning hours. Later outlooks may have to input prevailing TSRA
as confidence increases in direct impacts to the terminals.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Drake
LONG TERM...Gargan
AVIATION...Baerg


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