Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 180849

Area Forecast Discussion
National Weather Service Topeka KS
349 AM CDT Tue Apr 18 2017

.SHORT TERM...(Today and tonight)
Issued at 348 AM CDT Tue Apr 18 2017

An upper level trough was moving east across the northern plains
this morning. A surface cold front was moving southeast across
western NE and southeast SD. A strong LLJ across western and central
KS was transporting deeper gulf moisture northward. The resulting
isentropic lift across north central KS may cause some isolated
showers and elevated thunderstorms to develop across central KS and
move northeast across north central and northeast KS this morning.
The HRRR is the most aggressive showing elevated thunderstorms
developing across much of the western CWA by 12Z and moving these
showers east across the CWA through the mid and late morning hours.
The WRF solutions and GFS show isolated showers and elevated
thunderstorms developing by 12Z across the western counties of the
CWA and then moving northeast into NE during the mid morning hours.
The 06Z NAM develops elevated thunderstorms across west central KS,
well west of the CWA around 12Z and has the showers and storms
dissipating by 15Z. I`ll keep at least a slight chance for showers
thunderstorms in the forecast across the western and northern
counties of the CWA through 16Z.

Southerly winds will help to warm high temperatures into the upper
70s to around 80 across the CWA this afternoon.

A lee surface trough will deepen across eastern CO this afternoon,
thus the true dryline will only mix east to the NE and CO border
late this afternoon. The surface front in southern NE will become
stationary late this afternoon and through the evening. There may be
enough surface convergence along the front for scattered
thunderstorms to develop across southern NE during the late
afternoon and evening hours. The NAM and WRF solutions keep the
thunderstorms north of the NE border this afternoon and into the
evening hours. However, the WRF solutions try to back build the
thunderstorms west-southwest into the northern counties of the CWA
after 6Z. The GFS develops thunderstorms along the NE border, then
southwest across the western counties of the CWA. The GFS tries to
develop a pre-dryline trough across central KS which may provide
enough surface convergence to develop storms. At this time, I`m
going more with the NAM, WRF and RAP solutions. I may stick in
slight POPs across my western counties this evening to match up with
neighbors and just in case the GFS model may be more accurate with
thunderstorm development late this afternoon across north central
KS. But I think the only chance for thunderstorms Tonight will be
along the NE border late this evening and through the early morning
hours of Tuesday. If elevated storms do develop along the NE border
they could be strong or marginally severe given MUCAPE around 1500
J/KG and 0-6kM effective shear of 25-30KTS.

.LONG TERM...(Wednesday through Monday)
Issued at 348 AM CDT Tue Apr 18 2017

By Wednesday morning, models show an embedded shortwave trough over
Wyoming and northern Colorado with a surface low centered over the
far western KS/NE border. The associated cold front looks to be
draped across southern Nebraska Wednesday morning, with models
showing this boundary dipping into northwest to north central KS
late morning into early afternoon. As the shortwave trough advances
east-northeast into South Dakota and Nebraska, it will help to push
the cold front further into north central Kansas by mid/late
afternoon and into eastern Kansas by late evening.  A tight pressure
gradient is expected to set up over the forecast area through the
day. The resultant 25-35mph southerly wind gusts will support decent
WAA, boosting afternoon high temperatures well above the seasonal
normals. As temperatures soar into the upper 70s to low 80s, expect
increasing destablilzation through the afternoon with MUCAPE values
of 1000-2000 J/kg.  Model soundings show a significant cap in place
through much of the day, with the cap likely not eroding away until
very late afternoon or early evening.  As a result, much of
Wednesday is expected to be dry with short-range models showing
thunderstorm initiation along and ahead of the cold front not
occurring until after 21z.  With 35-45kts of 0-6km bulk shear in
place, strong to severe thunderstorms will be possible late
afternoon into the evening hours. Storms may initially develop as
discrete cells before congealing into a line of thunderstorms along
the cold front.  As a result, the primary threat initially will be
large hail and will transition more to a strong damaging wind threat
as storms become more linear. The severe threat looks to diminish by
late evening as cooler air advances into the region from the frontal
passage, and model soundings show storms becoming more elevated.
Some scattered light precipitation may linger across far east
central KS into Thursday, but the bulk of precipitation should be
focused southeast of the CWA along the exiting cold front. Overcast
skies will initially limit daytime warming on Thursday, but expect
diminishing cloud cover during the afternoon to allow high
temperatures to reach into the mid/upper 60s.

By Thursday morning, models show a mid-level trough over the Pacific
Northwest, with this trough digging further south as it advances
eastward over the Rockies on Friday.  While models are in fairly
decent agreement with the tracking of the mid-level low over the CWA
Friday night into Saturday, there are some discrepancies with the
exact tracking of the surface low and the amount of moisture
transport into the region.  The GFS/GEM are more aggressive with
precipitation chances from this advancing system, while the ECMWF is
weaker with this system and, thus, shows less QPF.  However, if the
more aggressive GFS/GEM solutions come to fruition, then there would
be the potential for moderate and possibly some locally heavy
rainfall as an abundance of moisture wraps around the surface low as
it slowly skims just south of the CWA.  This system will also be
accompanied by cooler conditions with east-northeasterly winds
keeping high temperatures Friday and Saturday in the 50s with low
temperatures in the 40s.

A mid-level ridge will build into the Northern and Central Plains on
Sunday behind this system, resulting in dry conditions Sunday into
Monday with temperatures moderating back into the 60s on Sunday and
near 70 degrees by Monday.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1152 PM CDT Mon Apr 17 2017

Have only made small changes to previous forecast. Still have
enough concern to include TEMPO MVFR cigs at all sites around 14Z,
and too little confidence in precip for inclusion.




LONG TERM...Hennecke
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