Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 230541
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1141 PM CST Sat Nov 22 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Sunday Noon)
Issued at 259 PM CST SAT NOV 22 2014

Many locations across the area have reached 60 degrees today, as
warm air streams northward across Kansas ahead of the southern
upper trof. Convection remains across Texas and Oklahoma, while
morning low clouds and drizzle have started to thin in afternoon
mixing.

Expect clouds and rain chances to return overnight, although
chances should be slight. By around sunrise, piece of the southern
wave lifts over the eastern part of the state and increases rain
chances. Even some elevated instability and a rumble of thunder is
possible especially east. Next cold front races into the north
central counties through the morning hours. Expect strong winds
and rain chances along with it.

.LONG TERM...(Sunday Afternoon through Saturday)
Issued at 259 PM CST SAT NOV 22 2014

By mid day Sunday the shortwave associated with the main trough
swings over the plains. This advancing trough will drive a cold
front into the forecast area from the northwest, which looks to
arrive in north central KS around 15Z. Further south a low pressure
will form over northeast OK and lift northeastward into MO. Strong
cold air advection behind the front will usher in temperatures into
the low 40s and upper 30s. A decent layer of frontogenesis will
coincide with the large scale lift to produce a post frontal band of
precipitation. This band will move into north central KS around 18Z
and progress eastward through the afternoon and early evening hours.
The predominate precipitation type will be rain especially
initially. As colder air filters in the sounding becomes almost
fully sub freezing with the exception of the boundary layer. Some of
the lift will occur in the dendritic growth layer with a deep layer
of saturation in place increasing the chances for ice crystals in
the cloud. These ice crystals have a good chance of melting in the
1500 ft warm layer at the surface. With full saturation wet bulb
temperatures may only cool the air to around 3 C. Although, if the
frontogenesis band precipitation is intense enough then you could
potentially cool this warm layer due to melting causing a brief
change over to a wet snow. Especially if the better lift
concentrates in the snow growth layer. At the moment I only
mentioned a chance for a rain snow mix. Do not expect any
accumulations at this time given temperatures in the morning will be
in the upper 50s and low 60s, and QPF generally under a quarter of
an inch.

The other issue behind the front will be the strong northwest flow.
Expect surface winds will quickly increase with the frontal passage
given winds at the top of the mixing layer will be around 45 kts and
a decent pressure gradient moves through. It does not appear that
winds will reach advisory criteria, but can not rule out 35 mph
gusts. Northwest flow aloft will dominate the extended, which will
be characterized by a few shortwaves translating across the northern
US. The most notable wave passes well north of us on Wednesday
dragging a cold front through the area bringing only an outside
chance of light precipitation. The GFS is less impressive with this
wave and therefore the cold air is slightly delayed until Thurs.
Surface pressure from Canada looks to take over for the remaining
period as the pattern aloft becomes more zonal. Temperatures will
generally be characterized by highs in the 40s and lows in the
20s.

&&

.AVIATION...(For the 06Z TAFs through 06Z Sunday Night)
Issued at 1140 PM CST SAT NOV 22 2014

For the 06z TAFs, southerly winds are gradually diminishing some for
the early overnight hours with MVFR cigs prevailing. As the
potential for drizzle increases overnight into Sunday morning,
expect cigs to drop to IFR and possibly even near LIFR conditions
with slightly reduced visibilities as well. However, sustained winds
of 7-10kts overnight into Sunday should reduce the potential for
widespread fog development and thus it should limit just how low
visibilities drop. The potential for light rain increases late
morning into the afternoon hours, and models continue to show the
potential for some weak elevated instability so have kept the
mention of VCTS in the TAFs. A cold front will track eastward during
the late morning and afternoon hours, resulting in winds veering
from south to northwest and wind speeds increasing behind the front
with gusts of at least 20-30kts. These winds will usher cooler air
into the region, resulting in the potential for a rain/snow mix
before the precipitation finally exits the TAF sites by late
evening.


&&

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

$$

SHORT TERM...67
LONG TERM...Sanders
AVIATION...Hennecke





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