Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 192325
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
625 PM CDT Thu Oct 19 2017

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Friday)
Issued at 300 PM CDT Thu Oct 19 2017

Water vapor loops this afternoon depict multiple, loosely phased
midlevel cyclonic circulations from the southern Rockies vicinity to
southwest TX. These perturbations will continue advancing north-
northeastward toward and across the central Great Plains through
late Friday afternoon. Meanwhile, the eastern rim of broadly
cyclonic flow aloft, peripheral to a longer-wavelength trough
amplifying over the western states, will begin overtaking the
aforementioned disturbances through the day on Friday. This will
favor lee cyclogenesis over the central and northern High Plains --
further tightening the surface pressure gradient across the region.
As a result, southerly surface winds will strengthen on Friday and
become gusty -- especially across north-central KS where sustained
winds reaching 25 to locally/briefly 30 mph are expected. However,
the anticipated marginal/brief/spotty nature of any advisory-level
winds precludes Wind Advisory issuance at this time. Moreover, any
large-scale ascent attendant to the loosely phased perturbations
should be quite modest and displaced to the north of richer deep
moisture -- greatly limiting precipitation chances. However, the
ascent should be sufficient for an increase in mid/high-level clouds
on Friday, while the increased southerly winds encourage some influx
of partially modified Gulf moisture.

.LONG TERM...(Friday night through Thursday)
Issued at 300 PM CDT Thu Oct 19 2017

Main focus is on the severe weather threat across the area on
Saturday. Strong cold front to push across Northeast and East
Central Kansas during the afternoon hours. NAM and GFS forecasts
show surface based CAPE values of 1500 to 2000 J/kg ahead of the
front with surface to 500 mb bulk shear values of 60 to 70kts.
Capping inversion should suppress convection initially in the
warm sector ahead of the front and would expect linear storm mode
to dominate given the strong forcing along the front. Main severe
weather threats will be large hail and damaging winds. Should also
be significant cloud to ground lightning associated with the
storms which will impact outdoor activities on Saturday afternoon.
Best potential for severe weather looks to be east of a line from
Marysville to Manhattan.

Beyond Monday, deep 500 mb trough over the Great Lakes will return
temperatures back to seasonable norms with highs in the 60s and lows
in the upper 30s to mid 40s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 623 PM CDT Thu Oct 19 2017

VFR conditions are expected through the period with 35 kts of
LLWS developing towards midnight and persisting into the mid
morning hours. Southerly surface winds will increase tomorrow
afternoon with sustained values of 15 to 25 kts with gusts of 25
to 35 kts.

&&

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

$$

SHORT TERM...Cohen
LONG TERM...Walawender
AVIATION...Skow



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