Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 201137

637 AM CDT Wed Aug 20 2014

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 234 AM CDT WED AUG 20 2014

Large-scale pattern over the Plains becoming more of a dirty ridge
regime with at to somewhat above normal precipitable water levels
across the bulk of the CONUS. Main troughs were over western North
America and the Great Lakes, with a minor upper wave in east central
Texas and 0Z observations showing a mid level trough over west
Texas. Since last night at this time, warm air advection and deep
moisture convergence has shifted northeast into Iowa where overnight
convection has erupted.

The Texas waves should be weakening with time with rather warm
column leading to limited saturation despite modestly above normal
PWs. Mid afternoon to evening hours exhibit little convective
inhibition but hard to think anything more than isolated storms
could result given limited forcing. Lower thermal fields showing
overall little change from Tuesday, with even minor cooling
suggested in some areas. Better mixing in the tighter surface
gradient and mixing of the 30-40kt low level jet should more than
offset any high cloud for highs to reach the mid to upper 90s again
with heat index values a few degrees higher yet. A slightly stronger
low level develops tonight, and with another day of heat today
expect temps to only fall into the mid to upper 70s.

.LONG TERM...(Thursday through Tuesday)
Issued at 234 AM CDT WED AUG 20 2014

Thursday and Friday the heat continues across the forecast area as
upper ridge slowly builds northward toward the upper Midwest.
850mb temps of 24-26c nose eastward out of the high plains into
eastern Kansas which brings surface temperatures well into the
upper 90s across most of the area. Longwave upper trof continues
to move eastward into the northern Rockies, with shortwave trof
moving into the upper Midwest late Thursday. Will keep low end
pops across the KS NE border where trailing front and nocturnal
llj may bring convection that far south although chances are
better farther north. Similar scenario plays out again in the
overnight hours Friday night.

Subtle differences in the larger scale pattern influence the
forecast through the weekend. EC is more pronounced with the
upper ridge into eastern Kansas, while the GFS flattens the ridge
more as energy moves out of the upper trof into the northern
Plains. How far east clouds and rain chances can extend east and
south will impact sensible weather through the weekend. Started
to bring rain chances farther east and south by Sunday, which leans
towards the GFS, but the strength of the ridge could certainly end
up toward a warmer drier EC solution on Sunday. North central
counties have better chances than farther east in this transition
period. Hopefully by Monday into Tuesday the longwave trof will
have made enough eastward progress to bring better rain chances
and a cooling trend in temperatures to our area. Worth noting
that both EC and GFS have a tropical system moving off the Mexico
coast by the end of the forecast period, which would likely
influence moisture transport into the longwave trof to its north
and could help rain chances for the forecast area. Have a slow
cooling in high temperatures from 90s on Saturday to low/middle
90s Sunday and back into the 80s for Monday and Tuesday.
Increasing rain chances by Monday and Tuesday with overnight lows
still on the warm side with 70s over the weekend to upper 60s by
Monday night.


.AVIATION...(For the 12Z TAFs through 12Z Thursday Morning)
Issued at 637 AM CDT WED AUG 20 2014

VFR conditions to continue. Will keep LLWS going for a few more
hours and could see redevelopment late tonight, though mixing
looks stronger tonight than in current hours. Some gusts still
likely through the afternoon.




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