Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 182314

Area Forecast Discussion
National Weather Service Topeka KS
614 PM CDT Fri May 18 2018

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Saturday)
Issued at 408 PM CDT Fri May 18 2018

Short-term forecast will be the period of most interest in the next
several days with a busy weekend of mid spring activities going on.
Bottom line is there is still some degree of uncertainty for severe
weather to impact the area over the next 24-36 hours.  But, it is
important to stress preparedness in the event that the worst case
scenario does play out.  Do expect all hazards to be possible over
portions of the area, especially focused north of I-70 from portions
of north central KS into northeast KS as the day progresses.

Currently, showers and a few storms still slowly progressing east
through the forecast area.  Coverage has become less over the past
hour in particular.  Have any showers coming to an end around 22-23Z
time frame. This is a remnant complex from overnight that was fueled
by a modestly strong LLJ that lasted into the mid day hours and
allowed just enough convergence and fuel for these elevated storms
to continue.  There have been some areas of wind gusts make it to
the surface as low level lapse rates steepened and showers have been
evaporating which has translated into enhanced momentum transfer to
the surface.  Temps this afternoon will generally have topped out in
the low to mid 80s with a few areas lower in the upper 70s that saw
early rainshowers.

Tonight, general agreement in a complex of showers and storms
getting organized within a upslope convergent area with surface low
pressure over or near the southeastern CO vicinity and advancing
east eventually in central and north central KS as the LLJ becomes
active once again and convergence takes place on the nose of the LLJ
keeping storms fueled into the overnight hours.  It isn`t
unreasonable that some smaller hail and stronger wind gusts make
their way into western counties.  Could be just enough for a
possible warning early in the evening as model soundings suggest a
shallow stable layer at the surface to be in place.

Into the day Saturday, this complex will likely impact what could
happen into the afternoon time frame and mesoscale details will
depend on where outflow boundaries setup into the morning and
afternoon time frame.  That said, upper flow into the region becomes
more southwesterly as a weak mid level ridge is pushed east of the
area.  Upper low deepens early in the day over northeastern CO
vicinity.  Lead shortwave will lift out over the central Plains into
the early to mid afternoon time frame.  Most models agree at the
surface there will be a surface low develop within an area of
inverted surface troughing over central KS into northeastern KS
where the warm front will sharpen through the day as it begin to
lift north (again, depending on how the mesoscale environment is
shifted based on morning convective complex).  It is worth noting
that also the GFS, NAM and Canadian solutions as well as most short-
term CAM guidance suggests there will be a period of clearing behind
morning convection.  This is the main concern if areas of clearing
do in fact take place that the set up will lend itself to all severe
hazards being possible.  However, the ECMWF does suggest that there
could be an expansive area of showers into the noon and early
afternoon (probably best case scenario which would mean less
opportunity for severe weather to later develop).  However, with
most suggestions hinting that deep layer shear does increase to
around 35-40kts and steep mid level lapse rates advect over the
surface boundaries allowing for MUCAPE values and MLCAPE values to
increase to the 4,000-5,000 J/kg ranges, the concern is that the
surface trough and low will become important into the afternoon as
well as the aforementioned warm front.  Hodographs in the vicinity of
the warm front also look favorable to support initially
supercellular development before transitioning into an linear
convective mode.  SRH values top over 200 m2/s2, so the environment
will be able to at least support concern for any supercells that do
develop to encompass a tornado risk into the mid to late afternoon.
The cold boundary/modified dryline will push through later in the
evening which could develop more storms into the evening time frame
with potentially training storms giving rise to a flash flooding
concern into the night time.  But, the main concern for severe
storms appears to focus along and north of I-70 for tomorrow with
updraft helicity values maximized over this region.

.LONG TERM...(Saturday night through Friday)
Issued at 408 PM CDT Fri May 18 2018

The long term forecast into late Sunday and next week for a more
zonal flow pattern early then a cut-off low feature setting up over
the western CONUS for middle week time frame.  Several periods of
showers and storms will be possible, but severe at this time appears
to be fairly low probability.  Temps remain generally in the 80s for
highs and lows in the 60s as we generally remain on the warm side of
the upper flow pattern.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 608 PM CDT Fri May 18 2018

A complex of storms is still possible late tonight although
confidence in the organization is low. Gusty winds would be the
main threat especially at MHK. Showers and isolated storms could
linger into the late morning hours. Severe storms capable of
producing large hail, damaging wind, and tornadoes are possible
early to mid afternoon tomorrow.




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