Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 172331
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
531 PM CST Sun Dec 17 2017

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Monday)
Issued at 254 PM CST Sun Dec 17 2017

Clouds overnight kept lows up into the lower 40s over much of the
area.  Despite lingering cloud cover, many areas have still made it
up near 50 thanks to a warmer start and some sunshine moving in from
the west under subsidence from the morning shortwave.  Stratus is
redeveloping over south central Kansas likely in response to another
wave in the southwesterly flow, and clouds look to return through
the evening hours before starting to clear out after midnight. As
clouds move east, and area remains bisected by a weak front,
anticipate light westerly winds and overnight lows in the 20s
northwest to upper 30s southeast where clouds clear last.  With
colder air still north of the state, highs climb back into the
middle to upper 50s for Monday.

.LONG TERM...(Monday night through Sunday)
Issued at 254 PM CST Sun Dec 17 2017

Towards mid week a mid-level closed low becomes cut off over the
western US. Ahead of that system lee side cyclogenesis supports a
deepening surface low pressure in eastern CO. An inverted surface
trough extending to the northeast of the low begins to push into our
area on Thursday. The low pressure is forecasted to track
northeastward along this trough as a lead wave lifts out over the
plains. Most of the dynamics associated with this lead wave occur
much further north than previous model runs. Some light
precipitation could skirt far northern KS, but this all depends on
the exact track of the lead wave. The western US closed low then
weakens and lifts out as a positively tilted open wave, but still
allows colder air to spill southward. Going into the weekend the
forecast gets tricky as another modest shortwave trough digs over
the western US. The models seem to be in better agreement that this
PV anomaly will interact and with the main polar vortex over
southern Canada. It is still unclear if there will be any partial
phasing or if the anomaly gets cut off. As of now the deterministic
models and a majority of the GEFS members lift this shortwave right
over the forecast area. It would provide enough lift for some
precipitation and given the arctic air mass in place it would be
snow. The models have struggled with this pattern shift and almost
every model cycle is slightly different than the one before so
confidence has remained low with how it will all unfold. If the PV
anomaly can partially phase and keep a neutral tilt then the going
forecast would be on track. If it becomes cut off then we will
likely be dry. The most influencing factor seems to be the positive
tilt of the polar vortex over southern Canada, which could prevent
any shortwave from really strengthening as it lifts out.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 531 PM CST Sun Dec 17 2017

VFR cigs along with a period of MVFR cigs are expected through 06Z
then expect clouds to clear with vfr cigs and vsbys.

&&

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

$$

SHORT TERM...67
LONG TERM...Sanders
AVIATION...53


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