000
FXUS63 KTOP 300520
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1120 PM CST Fri Nov 29 2013

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Saturday)
Issued at 347 PM CST FRI NOV 29 2013

Split upper level flow was observed across the CONUS Today. The
polar branch of the upper jet extended from the Gulf of AK,
east-southeast across western Canada into the Great Lakes States and
New England. The southern branch of the upper level jet rounded an
upper level trough about 500 miles southwest of LAX then extended
northeast across the northwest Mexico into the southern plains.

Tonight and Saturday, An H5 trough will dig southeast from
west-central Canada across the upper Midwest. This will cause a weak
front to push southward across the central plains through the
afternoon hours of Saturday. The front may reach the northwest
counties by late Saturday afternoon.

Southerly winds will keep overnight lows milder with temperatures
only dropping into the mid 20s to around 30 degrees.

Surface winds during the day on Saturday will veer to the southwest
and west through the afternoon hours ahead of the approaching cold
front. Wind speeds will decrease through the mid and late afternoon
hours as well. Mostly sunny skies will allow afternoon highs to
reach the lower to mid 50s across much of the CWA.

.LONG TERM...(Saturday Night through Friday)
Issued at 347 PM CST FRI NOV 29 2013

The latter part of the weekend continues to look quiet and dry as a
fairly zonal mid-level flow is in place over the central CONUS with
surface high pressure remaining anchored across much of the central
and eastern U.S. Models show a weak boundary passing southward over
the area Saturday night, with winds shifting around to the north on
Sunday. These light northerly winds should keep temperatures a few
degrees cooler than on Saturday, so have lowered Sunday high
temperatures by a couple of degrees into the upper 40s to lower 50s.

Sunday night into Monday, an embedded shortwave over the Dakotas
will track southeast of the area and result in a mid-level trough
developing over much of the eastern U.S. However, the main focus
will be with the system moving into the Pacific Northwest on Monday.
An expansive area of surface low pressure beneath this strengthening
mid-level low will extend into the Central Plains, with
southerly winds helping to boost Monday and Tuesday high
temperatures above normal into the low/mid 50s. As the surface low
quickly advances into the central Rockies on Tuesday, models are in
good agreement in having the pressure gradient tighten up over the
area on Tuesday. As a result, have started to trend upwards a bit
with wind speeds and may need to consider bumping temperatures up a
few degrees more if enough decent waa sets up over the region.

By Wednesday, the strong mid-level low will be advancing into the
Northern Plains with a trough extending across much of the western
U.S. This deepening trough will help to advance the surface low into
the region, however there is still model uncertainty with regards to
when the associated cold front will move into the area, further
influencing the temperature forecast. The GEM seems to be very fast
with the frontal passage and is an extreme outlier amongst the
models, so have discarded this solution. Between the GFS and ECMWF,
the GFS is a bit faster, bringing the front through Wednesday
morning while the ECMWF delays it until the afternoon. Models show
the potential for some light precipitation to develop generally
along and ahead of this front, however model soundings show a very
shallow layer of saturation in the low-levels as this system doesn`t
look to be able to tap into Gulf of Mexico moisture until after it
passes just east of the area. Due to the potential for limited
available moisture, have only slight to low-end chance pops for
Tuesday night into Wednesday. Models are showing surface high
pressure extending into the region behind this exiting low pressure
system Wednesday night into Thursday, bringing drier air into the
area. This drier air should help to push eastward any light
precipitation that`s able to develop in the first place, so have
trended downward with pops Wednesday night into Thursday to just
slight chances across extreme east central Kansas. If these model
trends continue, future forecast updates may be able to remove the
mention of precipitation altogether during that period. As for
temperatures, expect to see a wide spread in temperatures for
Wednesday with the frontal passage, but there is still some
uncertainty due to the discrepancies in the timing of the front. At
this time, have readings ranging from the middle 50s over east
central KS where southerly winds will be able to prevail longer
through the day to the middle 40s over north central KS as winds
shift to the northwest behind the front. The main impact from the
frontal passage will be the cold air that comes surging into the
Northern and Central Plains behind the front. By Thursday morning
models show 850mb temperatures plunging into the -2C to -8C range.
Breezy northerly winds will help to advect this colder air into the
area with high temperatures on Thursday only expected to reach into
the 30s.

The main mid-level trough will begin to advance across the Rockies
and toward the central U.S. by the end of the week into the weekend,
with a few embedded shortwaves expected to develop along the eastern
edge of the trough. This advancing trough will help to keep the cold
air in place over the area with Friday highs only reaching into the
mid/upper 20s and low temperatures dropping into the teens. While
models are in agreement in these shortwaves having enough lift to
produce some precipitation across the area, there is uncertainty in
the exact timing and tracking of any of these shortwaves. As a
result, have slight-chance to chance pops in for the Thursday night
through Friday timeframe. It`s important to note that with the surge
of cold air into the region, model soundings are currently showing the
potential for precipitation to be in the form of rain or snow with
any of the light precipitation lingering around Wednesday night into
Thursday and in the form of snow with any precipitation from the
embedded shortwaves Thursday night into Friday.

&&

.AVIATION...(For the 06Z TAFs through 06Z Saturday Night)
Issued at 1108 PM CST FRI NOV 29 2013

VFR conditions continue through the period. Winds become
southwest then northwest afternoon into late evening hours but
remain below 12kts.


&&

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

$$

SHORT TERM...Gargan
LONG TERM...Hennecke
AVIATION...67