Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 141757

National Weather Service Topeka KS
1257 PM CDT Fri Oct 14 2016

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 254 AM CDT Fri Oct 14 2016

Weak vorticity maxima was observed via water vapor imagery this
morning tracking across the central plains. Isentropic lift
upstream of the system developed light showers, producing trace
amounts of precip generally along and south of Interstate 35.
These showers will exit into MO by sunrise today as low level
moisture (around 900mb) from the south advects dewpoints into the
upper 50s by the afternoon. In addition, forecast soundings hold
on to a warm capping inversion above the moisture layer at 800 mb
throughout the afternoon, slowly mixing out from west to east over
the CWA. Believe that the low stratus may scatter out for
Manhattan, Emporia and points westward, while areas east are to
remain mostly cloudy. Therefore highs today were adjusted a few
degrees cooler over eastern Kansas into the upper 60s, while lower
to even mid 70s are possible over north central Kansas.

For tonight, southerly winds actually increase after midnight in
response to a lead shortwave trough over the Pacific Northwest
ejecting towards the northern plains. This in turn deepens the
surface lee trough all the way down to western Kansas. With the
higher dewpoints towards the sfc in place and the enhanced southerly
flow, should see the low stratus return overnight to much of the
area. There is a chance for patchy drizzle overnight especially
north of Interstate 70 where isentropic sfcs indicate weak lift in
the 900 to 850 mb range. With the stratus and warm southerly winds
towards Saturday morning, lows are much warmer than previous days
with readings in the lower 60s.

.LONG TERM...(Saturday through Thursday)
Issued at 254 AM CDT Fri Oct 14 2016

For Saturday through Monday, models are in good agreement that a
low level warm air advection pattern will persist with quasi-zonal
flow aloft. Within the pattern, low level moisture is progged to
return dewpoints in the mid and upper 60s to the forecast area.
But there is also an elevated mixed layer progged to cap the
boundary layer, especially for Sunday. There are signs from the
models of weak PVA Saturday afternoon and evening as a weakening
boundary moves close to the forecast area. However models seem to
think the cap will hold as they do not generate much in the way of
precip. Low level convergence along the boundary appears to be
marginal as surface winds tend to parallel the boundary from the
south southwest. If there was to be a thunderstorms, it would be
late in the day Saturday when forecast soundings from the NAM
suggest the least amount of CIN. The GFS forecast soundings keep
slightly more CIN and with no guidance generating any QPF, have
maintained a dry forecast for Saturday afternoon and evening. The
cap looks to be even stronger for Sunday and Monday with no
significant forcing so the forecast remains dry into Monday. Think
the biggest impact from the low level warm air advection pattern
could be low clouds. Models show low level saturations with the
advection of the moisture. Isentropic surfaces even suggest some
vertical motion within the stratus layer Saturday morning.
Because of this, have expanded the mention of patchy drizzle
Saturday morning to include the entire forecast area. At this time
I`m not anticipating any measurable precip so POPs remain less
than 20 percent. The main uncertainty for Saturday and Sunday is
how long the stratus may hang around and its impact on afternoon
temps. Have not strayed much from the model consensus on temps at
this point, but if it appears the stratus could hang in well into
the afternoon as some guidance suggests highs could be slightly
cooler. Nevertheless a warming trend should prevail through Monday
as southerly low level flow advects warmer air from the south and
southwest. It looks like the warmest day should be on Monday when
models mix the boundary layer to around 850MB as temps are progged
to be at their warmest at that level.

For Tuesday through Thursday, models show the pattern amplifying
as an upper trough deepens over the central part of the country.
There is good agreement on a cold front moving through the
forecast area on Tuesday with cold air advection increasing.
Models bring the front through dry with limited synoptic forcing
to overcome the EML over the warm sector. There are some slight
chance POPs in the forecast for Wednesday night and into Thursday
as the GFS and ECMWF show a secondary surge of cold air moving
through with the upper flow amplifying. This cold air advection
causes forecast soundings to steepen up with some mid level
saturation indicative of the possibility for some shower activity.
There doesn`t look to be much instability as lapse rates remain
near the moist adiabat. So have a slight chance for some showers
at this time. Temps should trend colder as a modified Canadian
airmass moves south. There are some differences in the strength of
the surface ridge by Thursday so adjustments to just how cool
temps may get are likely. For now have stayed with the model blend
which gives lows in the 40s and highs in the 60s by Thursday.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1243 PM CDT Fri Oct 14 2016

For the 18Z TAFs, continued moisture advection from the south
should help keep low clouds in place generally below 3kft through
much of the period. There may be some breaks in cloud cover this
afternoon, so have hinted at SCT deck during that period. But, not
expecting it to last long before going BKN again. Overnight, winds
increase at the surface and a LLJ overspreads the terminals around
2kft. Stratus deck overnight may not be thick enough to support as
much BR or DZ as this morning, so have only gone with BR which
model trends support at this time.




LONG TERM...Wolters
AVIATION...Drake is the U.S. government's official web portal to all federal, state and local government web resources and services.