Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 300425
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1125 PM CDT Sat Apr 29 2017

...AVIATION UPDATE...

.SHORT TERM...(This evening through Sunday)
Issued at 330 PM CDT Sat Apr 29 2017

At 2 PM Saturday, a strong short wave trough was crossing the
forecast area, kicking out from a powerful longer wave trough
centered near the Four-Corners region. This short wave will spell a
temporary break in precipitation for parts of the area although
strong mixing in its wake will lead to winds gusting 40+ mph for 1-2
hours this afternoon. Some higher res model guidance suggests
localized 50+ mph is possible but have not seen that materialize yet
so will monitor closely. Otherwise, areas generally along and
southeast of a Council Grove to Holton line will continue avoid the
brunt of the subsidence and will continue with scattered showers and
thunderstorms through the afternoon.

Numerous ingredients are in place for heavy rain but convection
farther to the southeast is eating a lot of the instability and
keeping the focus for heaviest rain out of the local area.
Regardless, with near-record precipitable water values in the area
and RAP soundings indicating the presence of up to 1000 J/kg at
times through the night, the potential does remain for some
localized flash flooding. Otherwise, it appears that several of our
river forecast points will at least approach flood stage and
possibly rise out of the banks into mainly minor flood stage. All
told though, the forecast is holding pretty well with the rain rates
not being too excessive to this point, and the substantial rain
totals being spread across many hours...thus limiting overall flood
potential.

Another short wave moves overhead around sunrise with a large area
of rain likely by that time frame as well, possibly coming to an end
before 10 AM depending on overall speed of the system. Thereafter,
the upper low moves out and re-organizes the surface low with a dry
slot likely to develop over parts of the CWA while a large area of
deformation precipitation develops on the northwest flank of the
system and impacts much of north central KS. This again will be a
long slow rain but may be sufficient to cause some generally minor
flooding. Do not expect any snow through the daytime hours (at least
in the TOP forecast area).

.LONG TERM...(Sunday night through Saturday)
Issued at 330 PM CDT Sat Apr 29 2017

The mid-level and surface lows associated with this weekend`s storm
system will be vertically stacked over the CWA by Sunday evening
before lifting northeastward into Iowa overnight into Monday
morning. Models continue to show a well-defined trowal north and
west of the low, with a dry slot moving into portions of southeast
and east central KS. As a result, the best potential for ongoing
precipitation Sunday night into Monday morning will be across north
central to northeast KS.  A very tight pressure gradient will be
present on the back side of this advancing surface low. As a result,
have increased the northwesterly winds with wind gusts upwards of 20-
30mph Sunday night and increasing to 25-35mph on Monday.  These
strong northwesterly winds will support strong CAA into the region
with Sunday night lows plunging into the mid 30s to near 40 degrees
from northwest to southeast across the CWA.  With surface
temperatures dropping to near the freezing mark, there is a slight
chance for some snow to mix in with the lingering light rain Sunday
night into Monday morning. However, model soundings show limited
saturation in the dendritic growth zone.  As a result, do not
anticipate any snow accumulation at this time.  Precipitation will
finally come to an end over northeast KS Monday morning with dry
conditions and clearing skies expected by the afternoon hours. These
clearing skies should allow for Monday high temperatures to quickly
reach into the upper 50s to low 60s.

As this strong mid-level low exits northeast, models show another
embedded shortwave developing within this mid-level trough. This
shortwave will likely track over the Rockies and progress
southeastward over the KS/OK border by midweek.  However, there is
still model uncertainty with the strength of this shortwave and,
thus the coverage of scattered precipitation.  At this time, have a
chance for scattered rain showers during the Tuesday afternoon
through Wednesday evening time period.  As this shortwave trough
progresses southeast of the CWA, models show it becoming a closed
low north of the Gulf of Mexico with an expansive mid-level ridge
developing over the western U.S. on Thursday and sliding eastward
into the Northern and High Plains on Friday and Saturday.  This
strong ridge will essentially create a blocking pattern, keeping the
closed low spinning north of the Gulf and a mid-level low near the
Pacific Northwest.  As a result, expect a period of dry conditions
Thursday through Saturday, with high temperatures moderating into
the 70s with lows in the 50s by Friday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday)
Issued at 1125 PM CDT Sat Apr 29 2017

Not a lot of change to the forecast. Models show potential for
light rain through early morning remaining high with isentropic
upglide across eastern KS. By mid day Sunday, the dry slot is
forecast to work its way into eastern KS. This may bring an end to
the widespread precip and allow CIGS to improve marginally.
Although plan to keep a VCSH as steep mid level lapse rates
associated with the upper low pass across the area. This could
allow a few showers or storms to develop. Warp around moisture and
a return to IFR conditions is likely Sunday evening.

&&

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

$$

SHORT TERM...Barjenbruch
LONG TERM...Hennecke
AVIATION...Wolters


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