Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 181149

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

...Update to aviation forecast discussion...

.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 then move northeast across north central and northeast KS
this morning. The HRRR is the most aggressive developing elevated
thunderstorms 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 tries 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 to marginally severe
given MUCAPE around 1500 J/KG and 0-6kM effective shear of

.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 12Z TAFS through 12Z Wednesday morning)
Issued at 640 AM CDT Tue Apr 18 2017

Low stratus is beginning to develop across central and southeast
KS. The stratus is moving north and there may be periods of
broken stratus with low MVFR ceilings through the mid morning
hours, before the boundary layer mixes deep enough to raise
ceilings to or above VFR criteria. Late Tonight the Low-level jet
will increase to 30 to 40 KTS and moderate low- level wind shear
will develop at the terminals after 6Z WED.




LONG TERM...Hennecke
AVIATION...Gargan is the U.S. government's official web portal to all federal, state and local government web resources and services.