Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 172104
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
404 PM CDT Wed May 17 2017

.SHORT TERM...(This evening through early Thursday afternoon)
Issued at 313 PM CDT Wed May 17 2017

Upper level and surface low pressure have tracked well northeast
of the area by 3 PM, with conditions drying out from this point
through the remainder of tonight. Strong pressure gradient and
resultant winds will continue in east central KS through sunset
but do expect a gradual decrease from the peak speeds that
occurred through 3 PM this afternoon. Elsewhere, winds will become
more westerly and eventually light later this evening.

The departing storm system will push a weak cold front into the
area but it looks likely to stall over southeast KS by early
Thursday morning. Southerly return flow will intensify quickly on
Thursday in advance of the next strong short wave trough. Low
level moisture will pool along the boundary as it lifts north
through the day. So, while the majority of the day will be
overcast and cooler, the warm front will approach I-70 by 00Z and
will set the stage for severe storms.

.LONG TERM...(Thursday evening through Wednesday) Issued at 313
PM CDT Wed May 17 2017

By early Thursday evening, expect strong to extreme instability to
be in place over southern Kansas and likely as far north as I-70.
The warm sector will be dominated by backed winds in advance of
strengthening surface low pressure in far southwest KS with a
negatively tilted lead short wave trough ejecting across KS. Deep
layer shear will be in the 40-50 kt range with clockwise turning
low level hodographs and low LCLs in the warm sector. This sets a
very favorable scenario for intense supercell development in south
central and perhaps southwest KS with the primary uncertainty
being how far east/west the initial development will occur.
Several pieces of guidance suggest warm sector development along a
confluence zone in south central KS by 00Z which is plausible
enough to pay close attention to it. If this happens, then these
storms would move across the warm sector into the local forecast
area and would likely be severe with all hazards possible
including tornadoes. Evolution through the late evening and
overnight is uncertain in detail but high confidence in storms
moving across the region after dark. There is some potential for
upscale growth into a QLCS but could also maintain quasi-discrete
supercell features with concern that the warm sector remains
unstable to surface based parcels...possibly continuing the all-
hazards threat well into the late evening or early morning.

On Friday, the stronger portion of the upper trough will eject
across the Plains with very strong wind shear and additional
severe potential. The main question on Friday will be how far
north the warm sector extends...which will be based largely on
what happens late Thursday night into early Friday morning in
terms of convective overturning and outflow. Within the warm
sector...wherever that may be...all hazards will again be
possible. At this time, see a good chance for the warm sector to
extend as far north as I-70 again but this is highly conditional.

Through this period, heavy rain will also be possible with
elements aligning for a heavy rain episode in north central KS on
Thursday night (which have been saturated by Tuesday night rain)
and in eastern Kansas on Friday. Flash flooding potential will
need to be closely monitored and WPC outlooks have suggested this
potential well in advance.

By Saturday, a dry period is expected through the weekend with
zonal to northwest flow. There will be a few weak disturbances
moving through this flow which could kick off a couple of rounds
of thunderstorms.


&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1236 PM CDT Wed May 17 2017

Aviation forecast focused on short term thunderstorm potential
through 21Z and tried to focus on the most likely hour of impact
although it could vary a bit. Winds will shift through the night
turning out of the east by Thursday morning with a good chance for
MVFR cigs to build over TAF sites after sunrise.


&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Barjenbruch
LONG TERM...Barjenbruch
AVIATION...Barjenbruch



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