Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 282332 AAA
AFDTOP

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TOPEKA KS
632 PM CDT Sun Sep 28 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Monday)
Issued at 317 PM CDT SUN SEP 28 2014

Quiet weather is expected through Monday as surface high pressure
remains near or just east of the forecast area and a weak upper
ridge builds overhead. May still see an isolated shower or even
t-storm through around 5 PM today as a weak vort max drifts across
the area but this chance is minimal and it`s likely that everyone
will stay dry. Sunday night through Monday will be dry throughout.
Temperatures are expected to be more-or-less a carbon copy of the
previous 24 hours...with overnight lows in the upper 50s to around
60 and highs on Monday in the low to middle 80s. Could see patchy
fog in valleys again on Monday morning as well, and while fog near
rivers/lakes could be dense at times, it should be quite patchy and
impacts likely to be minimal.

.LONG TERM...(Monday Night through Sunday)
Issued at 317 PM CDT SUN SEP 28 2014

By Tuesday morning the strong lead shortwave begins to eject out of
the Rockies. As that system ejects the pressure fields decreases and
wind field increase which helps pull higher dew points back into the
region. Also, a strong jet streak will round the base of the
trough and pass over the high plains where the surface low
pressure forms. A trailing cold front will extend southward into
western KS. Warm advection isentropic lift ahead of the PVA brings
a chance for showers and thunderstorms into north central KS
during the morning hours. Mid level lapse rates are not that
impressive leading to limited instability despite the deep layer
shear around 30 kt. The overall system lifts north northeast which
will limit the eastward progression of the front. The complication
becomes if the morning activity can clear out in time for daytime
mixing to occur. If there is a window of clearing than instability
could increase to 2000 j/kg while the deep layer also increases to
45 mph, which is supportive of severe storms. The front as well as
an axis of instability just west of the area will become the
focus for convection during the afternoon and evening hours. It is
this time frame a strong to severe could move into north central
KS. Expect that storm intensity will decrease further east into
the forecast area during the overnight hours with the limited
instability in those areas. Although coverage is likely to increase as
a weak shortwave passes over the region within the southwest flow
aloft.

The main mid/upper level trough axis over the strong deep layer
forcing along and ahead of the front will begin to progress eastward
on Wednesday. At the same time a sfc low will develop along the
front in northwest OK with a weak warm front extending eastward. Dew
points south of the warm front will exceed 65 degrees although not
sure how far north the front will lift. At this point it is possible
to reach as far north as interstate 70, but is more likely to set up
further south in east central KS. The other main question is will
there be any clearing to allow more surface heating with deep layer
shear approaching 50 kts. Also, subsidence is possible during the
day Wednesday behind the departing shortwave could allow for this
window. Attention is still needed since low cape and high shear
environments are well conducive for severe weather. The NAM forecast
soundings for Wednesday evening depict cape around 2500 j/kg and
high SRH values across east central KS.

The models begin to disagree on the speed of the main trough axis
and the front sliding through the area. The ECMWF is much faster and
the front exits Wednesday night while the GFS is about 12 hrs
slower. Post frontal showers and thunderstorms are possible during
the day Thursday as the main trough axis moves through. Clearing is
likely to take place by at least Thursday night. Strong advection
behind the system will bring in cooler temperatures into the
region.

&&

.AVIATION...(For the 00Z TAFs through 00Z Monday Evening)
Issued at 626 PM CDT SUN SEP 28 2014

Will maintain persistence this fcst with VFR conditions at KMHK
and MVFR/IFR vsbys in fog primarily in the 09z/13z time frame at
KTOP and KFOE terminals. Otherwise expect TAF fcsts to be VFR
with only a few stratocu and southeast winds generally under 7kts.

&&

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

$$

SHORT TERM...Barjenbruch
LONG TERM...Sanders
AVIATION...63





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