Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 222040
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
340 PM CDT FRI APR 22 2016

.SHORT TERM...(This Evening through Saturday)
Issued at 336 PM CDT FRI APR 22 2016

Low level stratus clouds have dissipated across much of east central
Kansas and should be completely gone by late afternoon. The surface
trough axis extended south into north central Kansas and will move
eastward this evening and overnight as low pressure deepens over the
high plains. Warm advection occurs tonight across western and
central Kansas and continues on Saturday across the area. Lows
tonight will cool off into the upper 40s to lower 50s.

Forecast soundings show mixing up to 850 mb on Saturday with high
temperatures ranging from the upper 70s to lower 80s. Southerly
winds will also increase through the day with wind gusts in the
afternoon of 24 mph to 37 mph with the higher gusts west of
Manhattan as we mix down stronger winds aloft.

.LONG TERM...(Saturday Night through Friday)
Issued at 336 PM CDT FRI APR 22 2016

Saturday Night through Monday...

An upper level trough located across the four corners region
Saturday evening will slowly lift northeast across NE and western
KS, then the upper trough will lift northeast across eastern NE
and eastern KS into southwest MN and northwest MO by 12Z MON.

Ahead of the upper trough the LLJ will increase from the south-
southwest at 40 to 50 KTS and transport deeper moisture northeast
across central and northeast KS after 6Z SUN. The combination of
isentropic lift ahead of the deeper moisture and ascent ahead of the
LLJ may cause some isolated elevated thunderstorms to develop during
the early through mid morning hours of Sunday. These storms should
diminish and move northeast of the CWA by the mid morning hours of
the CWA.

During the afternoon hours the GFS and NAM both show a surface
dryline/pacific front moving eastward across the western CWA.
Thunderstorms will develop along and perhaps ahead of the front
within the warm sector. Initially these storms may remain discrete
but as the the stronger ascent shifts eastward across the area the
discrete thunderstorms may develop into line segments or a squall
line through the late afternoon hours. The 12Z NAM model develops
2,000 to 3,000 J/KG of MLCAPE by 00Z, where the 12Z GFS only
develops 1,000 to 1500 J/KG of MLCAPE. My thoughts are the NAM may
be over doing MLCAPE a bit and the MLCAPE may be under done on the
GFS. We`ll probably see 1500-2500 J/KG of MLCAPE developing during
the afternoon hours. Temperatures will be warm with highs in the
upper 70s to around 80 degrees. Initially, 0-1 KM SRH will be under
100 J/KG during the afternoon hours, due to slightly veered surface
and 850 MB winds, thus any discrete supercell may not have an
environment favorable enough to produce tornadoes. I think large
hail and damaging wind gusts will be the greatest hazard. As the
scattered supercells congeal into a line of storms the main hazard
will become more of a widespread damaging wind threat across
northeast and east central KS through the early evening hours. The
H5 flow will increase to 55 to 60 KT through the evening and surface
winds may back more to the south. The 12Z NAM shows the 0-1 KM SRH
increasing to 200-300 J/KG by 3Z, so if there were any discrete
supercells than there could be a tornado threat across east central
KS during the evening hours, however, due to the stronger ascent
ahead of the H5 trough moving across east central KS, any discrete
or scattered storms may have congealed in to line segments or a
squall line. I suppose you could not rule out meso-vortices forming
along the line of storms during the evening hours.

As the H5 trough lifts northeast of the area, the line of storms
should move into western MO after midnight. A weak cold front will
move southeast across the CWA during the early morning hours of
Monday. The ECMWF shows this front stalling out across our southeast
counties. The GFS pushes the front southward into southeast KS,
before it becomes stationary.

Monday, The surface cold front will be nearly stationary across our
southeast counties, or across southeast KS if the GFS model is more
accurate. At this time I will keep the front across our southeast
counties. Monday afternoon there may be a slight chance for isolated
showers and thunderstorms developing along the the surface front,
generally along and southeast of I-35. Given weak low-level winds
and ridging at mid levels, any storm that develops should not be
severe. Although the NAM develops 1500 J/KG of MLCAPE along and
north of the front. In fact the 18Z NAM lifts the front northward to
a Holton, to Topeka, to Council Grove line by 00Z TUE. So there may
be a slight chance of thunderstorms across much of east central KS.
Highs on Monday will be slightly cooler with mid to upper 70s.

Monday Night through Friday...

Slight chances for scattered elevated thunderstorms Monday night
into Tuesday morning as moisture advection increases and weak
isentropic lift within the 300-305K layer overspreads the area. The
big question mark during the extended period is the timing of the
upper level trough along with the surface dryline and warm front on
Tuesday. Current 12Z guidance from the ECMWF and GFS continues to
place a sharp dryline along the Interstate 35/135 corridor.
Confidence in the placement of the warm front is still low at this
point as the faster ECMWF advances the front to the KS/NE border,
whereas the slower GFS is closer to the Interstate 70 corridor.
Plentiful BL moisture will plume northward within the warm sector as
dew points will surge into the low to mid 60s by Tuesday afternoon.
Any thunderstorm that develops along the dryline is expected to be
surface-based supercells with all modes of severe weather possible
as surface-base CAPE 2000+ and 0-6KM shear values in the 40-50 knot
range. Development along the warm front is still a question mark, as
forecast soundings from both the ECMWF and GFS continue to keep
surface parcels "capped", mostly due to limited surface heating from
cloud cover. However, elevated supercells appear likely along and
north of the warm front with the main hazards being very large hail
and damaging winds.

Another upper level trough will eject across the central and
southern plains Thursday night and Friday, returning the chances
for thunderstorms to the area

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 1156 AM CDT FRI APR 22 2016

For the 18z TAFs, VFR conditions should hold for the afternoon
into the evening as current stratus deck continues to erode with
the heating of the day. Not confident enough at this point to add
fog for the 11-13Z time frame in the morning. However, there is a
possibility for some reduced VIS and patchy FG around 12Z mainly
at KTOP/KFOE. Have left mention out of the TAFs for now, but this
will be something to monitor TAFs for if decoupling allows for the
set up to occur. Winds will increase by late morning from the
SSE.


&&

.TOP Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...53
LONG TERM...Baerg/Gargan
AVIATION...Drake



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