Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 191129
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
629 AM CDT Tue Sep 19 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 306 AM CDT Tue Sep 19 2017

Southwest flow continues over northeast Kansas with another chance
for some morning showers and storms as the turning low level jet
enhances isentropic lift over the area.  These storms are expected
to move eastward and dissipate by late morning. The main upper
level trough over Alberta shifts eastward during the day today
acting to enhance the pressure gradient over the area. Windy
conditions are expected this afternoon with sustained winds
ranging from 20 to 30 mph, with gusts up to 40 mph especially near
central Kansas. Conditions look a bit borderline, but went ahead
and opted for the Wind Advisory for portions of the area this
afternoon. On top of the wind, a hot day is expected with highs
reaching into the low 90s in north central Kansas to upper 80s in
very eastern Kansas. With dewpoints in the upper 60s and low 70s
this afternoon, outside conditions will be muggy. The GFS shows a
weak midlevel wave transversing the area early evening possibly
generating an isolated storm , but overall consensus is for dry
conditions today and tonight. Towards the very end of the period,
a surface front moves towards the area causing lows to range from
the low 60s in north central Kansas to the low 70s in east central
Kansas.

.LONG TERM...(Wednesday through Monday)
Issued at 306 AM CDT Tue Sep 19 2017

On Wednesday a cold front will push through the area as a shortwave
trough lifts over the upper Midwest. The front gradually moves
eastward during the day and reaches portions of east central KS by
the early evening. Most of the model soundings show that surface
based parcels will be capped despite surface heating. Also the upper
level support is rather removed from the region so forcing should be
overall weak. By the evening the NAM shows moisture advection over
the frontal surface which may allow elevated parcels to become
unstable. The GFS is less aggressive with this moisture, but if
realized the elevated parcels will have a weaker cap to deal with.
If the mesoscale forcing is enough there is a chance that storms
form along the front may around sunset give or take a few hours. The
front should be in the vicinity of the Kansas turnpike during this
time frame. Given the high moisture content the cape is expected to
be rather high, while the deep layer shear is marginal. If storms
develop they should stay isolated to scattered and capable of
producing large hail and perhaps damaging wind gusts. The chances
could linger into the overnight as the GFS is advertising for some
deep isentropic lift, which could support lingering precipitation
mainly across eastern KS. A majority of the GEFS members have at
least some QPF by sunrise Thursday morning at these locations so the
current pops seem justified. It is hard to call this a cold front
since temperatures will recover fairly quickly and reach the 90s on
Thursday.

The weather should be quiet and rather windy through the early
weekend. Although there could be some nocturnal warm air advection
precipitation once the return flow gets established. As a longwave
trough deepens over the western US a lee side trough will set up in
the high plains. Therefore the surface pressure gradient becomes
maximized across the area. It appears that the upper level system is
slow enough to keep the frontal zone west of the forecast area
through most of the weekend. The models are suggesting there could
be two main pieces of shortwave energy within the longwave trough.
One over the northern Rockies and the other over the southwest US. A
third shortwave over Canada looks to get become an open wave and get
picked up by the westerlies. This should be the energy that dictates
the eastward movement of the front. Given this forecast the only
locations that could receive precipitation from the front will be
north central KS perhaps as early as Saturday night. The northern
Rockies shortwave finally lifts out over the northern plains on
Monday so the front should push into eastern KS. Expect that more
widespread showers and storms will continue through Tuesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 629 AM CDT Tue Sep 19 2017

VFR conditions are expected for the period. Gusty southerly winds
are expected to pick up this morning with the strongest gusts up
to 25 to 30 kts after 18Z this afternoon. Winds stay gusty through
the night. There is a signal for LLWS tomorrow morning, but due to
the stronger overnight winds it could be a marginal case and will
hold off this TAF issuance.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 1 PM this afternoon to 7 PM CDT this evening
for KSZ008-009-020>022-034>038.

&&

$$

SHORT TERM...Heller
LONG TERM...Sanders
AVIATION...Heller


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