Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 120500
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1200 AM CDT Fri Sep 12 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Friday)
Issued at 324 PM CDT THU SEP 11 2014

Water vapor imagery this afternoon continues to highlight the
positively tilted upper trough deepening southeast over southern
Montana into Wyoming. The core of the colder air aloft was beginning
to enter the northern plains. Edge of the vorticity maxima was
beginning to push into northern Nebraska where scattered showers and
thunderstorms were developing. Persistent cloud cover and northerly
CAA hindered afternoon highs to the upper 50s and low 60s. Expect
this trend of cooler temps to continue this evening and Friday as
skies become overcast from the northwest. As the open wave
approaches the central plains, low to mid level frontogenesis
through 700 mb enhances over Nebraska into northeast Kansas.
Scattered light to moderate showers are progged to form over
Nebraska and spread into the CWA late this evening through tomorrow
afternoon. Adjusted POPs this evening based on short term model
trending a bit slower than previous forecast. Best chances for rain
showers are around midnight through 6 AM over north central areas.
Across east central Kansas, sunrise through the afternoon are
optimal for scattered light showers. Decreasing frontogenetical
forcing from north to south suggest intensity of the rain showers to
weaken throughout the day as cold and drier air quickly enters north
central KS.

Mostly cloudy to overcast skies this evening drop overnight lows to
the upper 40s and lower 50s. Highs tomorrow are a bit tricky
dependent on thickness of cloud cover and coverage of precipitation.
The second, stronger surge of cold air arrives during the afternoon
as h85 temps fall to the single digits by 00Z. Most ensemble
guidance trends highs over east central KS into the lower 60s before
the cooler air arrives late afternoon. Precip clearing out by late
afternoon over north central KS may help highs into the lower 50s.

.LONG TERM...(Friday Night through Thursday)
Issued at 324 PM CDT THU SEP 11 2014

By Friday evening chances for precip quickly diminish as dry air
overtakes the region and lift moves off to the northeast and south.
The only expectation would be light rain and or drizzle lingering into
the early evening hours especially in east central KS. high pressure
ridge will build in from the northwest causing a decrease in the
pressure gradient so expect diminishing winds through out the
evening. One uncertainty will be how quickly the clouds move out of
the area with the cold dry air advection. This will play a role in
how much of the recent rainfall the sun can evaporate as well as
development of the nocturnal inversion. That being said the fall
like air mass, clear skies, and light winds early Saturday morning
will set the stage for unseasonably cold temps, and the potential
for radiation fog. Saturday morning low temps range from the upper
30s to low 40s. Fog is still more likely than frost at this point
with dewpoints only reaching as low as the upper 30s. The NAM is
most aggressive with a strong inversion and saturation in the
boundary layer as opposed to the GFS. Have held off adding patchy
fog to the forecast due to the uncertainty.

Return flow quickly develops ahead of the next system, which is
forecast to clip the area on Monday. The models still in agreement
with the speed and placement of the front during the day Friday, but
the high pressure placement is still off. Instability does return
shortly ahead of this system increasing the potential for
thunderstorms. Have gone with the ECMWF and GEM which depict a
stronger high centered further south and west than the GFS. This
should clear the precip out faster behind the front on Monday night.
On Wednesday and Thursday models hinting at a weak wave in the
northwest flow aloft therefore have kept slight chances for
thunderstorms with instability building back into the region. The
models completely diverge with regards to the pattern aloft by mid
to late week. Most of the GFS ensemble members do not support the
operational run leading to a large standard deviation in 500 mb
heights. Temps eventually warm into the 80s by the end of the
period.

&&

.AVIATION...(For the 06Z TAFs through 06Z Friday Night)
Issued at 1157 PM CDT THU SEP 11 2014

Current MVFR ceilings will build below 2000 feet by around 06Z.
Scattered light showers will also gradually increase in coverage,
but should not be significant enough to cause additional flight
restrictions until after 12Z. Between 12Z and 15Z, a band of
moderate rain is likely to impact TAF sites with periods of
reduced vis and cigs probably falling into IFR category. IFR
conditions should persist for 2-3 hours with a gradual increase
in conditions through the rest of the day. Uncertain regarding
timing of MVFR cig scattering out, but seems that between 03Z and
06Z is the most likely time.

&&

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

$$

SHORT TERM...Bowen
LONG TERM...Sanders
AVIATION...Barjenbruch






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