Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 112332
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
632 PM CDT Thu Sep 11 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 00Z TAFs through 00Z Friday Evening)
Issued at 618 PM CDT THU SEP 11 2014

MVFR ceilings currently in place will gradually lower into the
1000-1500 ft range through tonight as the low levels cool and
more low level moisture moves into the area. Between 11Z and 14Z,
expect rain showers to begin to impact TAF sites. There may be
a period prior to 17Z for which cig or vis reaches IFR conditions
with a band of moderate rain, but at this time MVFR seems more
likely. Expect precip to decrease and end by early afternoon with
cigs gradually improving toward 2500 ft by mid afternoon

&&

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

$$

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






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