Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 192051
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
351 PM CDT Sat Aug 19 2017

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Sunday)
Issued at 349 PM CDT Sat Aug 19 2017

As of 20z Saturday afternoon, a remnant weak surface trough was
positioned from central KS into southern MO. A very buoyant
atmosphere resides along and south of the boundary with MLcape
values >3000 J/KG. Veering wind profile has resulted in effective
shear approaching 30kts, sufficient for rotating updrafts. Bunkers`
motion for right moving supercells is south-southeast, therefore
expect bulk of activity to stay south of the area. Zonal to slight
northwest flow aloft reside across the central and northern Plains.
Water vapor analysis reveals a subtle shortwave across eastern WY.

As we transition into the evening and overnight hours, leeward
cyclogenesis will continue to develop in northeastern CO. Good
agreement amongst model guidance with developing showers and storms
in western NE. Consensus suggests the bulk of activity will enter
north central KS near midnight. The biggest question mark remains,
the eastern extent of PoPs overnight. Given the weakly sheared
environment ~20kts, expect any upscale growth to quickly become cold
pool dominate. A ~30-35kt LLJ could provide some MCS maintenance
through 06-09Z. As the LLJ veers and weakens, expect activity to
weaken and diminish across eastern KS. Skies are expected to clear
from west to east Sunday morning, yielding mostly sunny skies by
early afternoon. H850 temperatures will touch the mid 20s C in
central KS, resulting in surface temperatures approaching the century
mark. Surface trough will develop across southern NE Sunday
afternoon. Given the plentiful BL moisture and steep mid level lapse
rates, an isolated storm or 2 cannot be ruled out in far northern
KS.

.LONG TERM...(Sunday night through Saturday)
Issued at 349 PM CDT Sat Aug 19 2017

For Sunday night and Monday, models show southwesterly flow aloft
while the deeper moisture axis remains over eastern KS. There are
also signals for increasing vorticity advection by Monday afternoon.
So with some instability likely (lapse rates around 7 C/km), there
remains some chance for scattered showers and thunderstorms.
Unfortunately for eclipse watchers, the moisture and instability
from the models have sky cover trending more towards mostly cloudy
during the eclipse. It still doesn`t look like skies will be
overcast so it may not be a complete loss but sky conditions do not
look favorable Monday afternoon across northeast KS. Have trended
highs Monday a degree or two cooler anticipating at least partly
cloudy skies. Also the loss of insolation during the eclipse may
slow down the normal diurnal warm up.

For monday night and Tuesday, showers and thunderstorms are likely
as models agree on a synoptic shortwave moving through the upper
Midwest bringing a cold front through the area. It appears that the
most likely timing for precip will be during the early morning hours
Tuesday as the frontal boundary moves through.

For Tuesday evening the front is progged to be south of the forecast
area with cooler and dryer air moving south. A surface ridge of high
pressure is expected to persist over the area into Friday with below
normal temperatures and dry weather forecast.
The GFS and ECMWF show this ridge weakening by Friday night with a
return flow developing. So there are some small POPs Friday night
and Saturday anticipating an increase in warm air and moisture
advection.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 349 PM CDT Sat Aug 19 2017

VFR conditions are expected throughout the period. Continue with
the mention of VCTS at all terminals overnight. Will continue to
monitor convective trends through the evening hours, as the best
storm chances may stay north of the terminals. Otherwise, light
southeasterly winds are expected between 5 and 10 kts.

&&

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

$$

SHORT TERM...Baerg
LONG TERM...Wolters
AVIATION...Baerg



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