Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 211110
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
510 AM CST Sun Dec 21 2014

...AVIATION UPDATE...

.SHORT TERM...(Today and Tonight)
Issued at 233 AM CST SUN DEC 21 2014

08Z water vapor shows a broad upper level trough over the central
part of the country with the upper level jet streak moving inland
over the pacific northwest. At the surface, a trough of low pressure
has gradually be moving out into the northern plains while surface
ridging remained along the gulf coast. An area of stratus could be
seen on satellite moving back north into the forecast area.

For today, the southerly low level flow between the surface trough
to the northwest and ridging southeast of the forecast area should
continue bringing moisture north. Although with the gulf not
completely open due to the ridge axis along the coast, dewpoints are
progged to only increase to around 40 today which makes some since
looking at obs across OK and north TX. This moisture advection
should be enough however to keep the stratus moving north. The NAM
and RAP develop some weak isentropic upglide on the 280 and 285K
surfaces this morning and keep it persisting into the afternoon.
Because of this will maintain a mention of drizzle in the forecast
through the day. Weak large scale forcing and little or no deep
vertical motion to moisten the mid levels leads me to think
measurable precip is less than 20 percent through the day. Cloud
cover should prevent temps from warming much today, so have highs
generally in the mid 40s. Models continue to deepen a shortwave
tonight over NEB. As the wave deepens, models prog some decent PVA
and increasing Q vector convergence to overspread northeast KS. Mid
level lapse rates appear to be near the moist adiabat so there does
not appear to be much in the way of instability. Nevertheless the
increasing forcing and decent moisture already in place should lead
to some rain showers moving into parts of the forecast area late
tonight and through the early morning hours Monday. Have increased
POPs with likely chances for northeast KS and chances diminishing
further south where model progs of forcing are not as strong.
Southerly winds keeping dewpoints in the upper 30s combined with
overcast skies and no radiational cooling should lead to min temps
in the lower 40s for most areas.

.LONG TERM...(Monday through Saturday)
Issued at 233 AM CST SUN DEC 21 2014

Rain showers may linger across east central Kansas Monday as the
upper low slowly rotates over South Dakota. Amount of dry air aloft
differs between guidance and is based on the strength and track of
the upper low. Thinking the dry air intruding may be too progressive
with the NAM, so sided with the slower GFS/ECMWF solution and
therefore mostly cloudy skies for the afternoon. Warm air advection
in the lower levels warms temps to near 50 degrees ahead of the
front. As an upper jet dives southeast from the Rockies, it will dig
the southern stream wave further south and east into Texas while
gradually lifting the upper low northward through Tuesday. In
conjunction with a surface front arriving early Tuesday, embedded
areas of enhanced vorticity wrapping around the upper low may
produce light snow near the Kansas and Nebraska border. Otherwise
most areas remain dry through the afternoon with highs rising a few
degrees from morning lows into the 30s. Amount of stratus will once
again depend on the upper low position. It is possible southern areas
could see lesser cloud cover in the afternoon. In addition, strong
northerly winds are expected Tuesday afternoon between 15 and 25 mph
sustained from the northwest. Gusts near 35 mph are likely
especially for north central Kansas.

Airmass modifies as winds back to the south in advance of a lee
trough Wednesday and Christmas Day. Southerly winds between 10 and
15 mph carry warm, subsident air across the CWA, raising highs from
near 40 on Wednesday to upper 40s for Christmas Day. During this
time, a shortwave trough develops across the western CONUS, bringing
rain and snow to elevated terrain. As it enters the central plains,
questions still remain on the depth and track. Latest ECMWF today
exhibits a very different solution with an open short wave trough
impacting the central plains Thursday evening/Friday, similar to
what the GFS has advertised the past few days. Did not feel
comfortable completely removing pops given the large
inconsistencies, and will therefore leave slight chances until
better consistency is seen one way or the other. A cold air mass
behind the front is more likely, dropping highs Friday and Saturday
in the 30s. Forecast soundings suggest any precip would be in the
form of light snow.

&&

.AVIATION...(For the 12Z TAFs through 12Z Monday Morning)
Issued at 509 AM CST SUN DEC 21 2014

Satellite continues to show MVFR stratus advancing northeast, and
with southerly flow expected to maintain some moisture transport
north think the stratus will hang tough through tonight. Models
continue to show increasing isentropic lift through the afternoon
so drizzle is possible. Confidence in timing is low so opted to
keep VSBY forecast in the MVFR range. However if drizzle develops,
it will likely cause VSBY to be between 1SM and 3SM. Have also
leaned towards keeping CIGS above 1 KFT but there could be some
periods where CIGS drop below 1 KFT. Increasing large scale
forcing late tonight should lead to some -RA moving into the
terminals between 07Z and 09Z.

&&

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

&&

$$

SHORT TERM...Wolters
LONG TERM...Bowen
AVIATION...Wolters





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