Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 191118
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
518 AM CST Fri Dec 19 2014

...AVIATION UPDATE...

.SHORT TERM...(Today and Tonight)
Issued at 246 AM CST FRI DEC 19 2014

08Z water vapor imagery indicated there were a couple waves within a
somewhat slow split flow over the plains. The stronger wave was
lifting through the southern plains with some decent lightning noted
in eastern TX. A second weaker wave was noted over southeastern MT.
At the surface a high pressure system centered over the central and
upper MS river valley was nosing into eastern KS with a ridge axis
bisecting the forecast area.

For today and tonight, the better forcing from the shortwaves looks
to only glance the forecast area. Forecast soundings from the
RAP/NAM/GFS indicated a decent amount of dry air in the mid levels
and prog a westerly wind at 850 and above to continue advecting dry
air in from the west. So with the weak forcing unlikely to overcome
the dry air in mid levels, have maintained a dry forecast through
tonight. Really the main forecast challenge is the boundary layer
moisture and pesky stratus. All the models fall to mix out the low
level inversion and the boundary layer moisture. This seems to make
some since with the expansive stratus deck already in place and snow
cover limiting any insolation to warm surface temps. Therefore have
leaned towards an overcast sky through tonight. Isentropic surfaces
show only weak if any isentropic upglide and appear to focus this
mainly across MO, so concerns for drizzle are minimal today as well.
About the only uncertainty with the forecast is the NAM`s tendency
to over due the impact of the snow cover and keeping the boundary
layer to cool for to long. However with the GFS and RAP showing
similar solutions, think the low clouds scattering out is a low
chance occurrence. Highs today are expected to be in the mid 30s
with no real low level warm air advection and clouds holding on
strong. For tonight have kept skies cloudy, but if for some reason
we were to clear out, fog would become more likely. I don`t have a
lot of confidence in this happening. Nevertheless have added a
mention of patchy fog after midnight due to forecast soundings
showing the potential for some fog, especially across north central
KS. Lows tonight are expected to range from the mid 20 to around 30.

.LONG TERM...(Saturday through Thursday)
Issued at 246 AM CST FRI DEC 19 2014

Patchy fog is expected to linger through mid morning Saturday before
lifting to mostly cloudy stratus. A developing surface trough over
eastern CO will pick up winds around 10 mph, attempting to mix out
the stratus in the lower levels. Best chances for seeing peeks of
sunshine lie across central KS, with much of the CWA remaining
cloudy. Despite the warmer temps from guidance, believe the
lingering snow cover holds highs a few degrees cooler in north
central and far northeast KS where upper 30s are common. Areas with
little to no snow cover may reach the lower to middle 40s. Surface
trough begins to deepen on Sunday in response to the upper shortwave
trough coming onshore from the Pacific NW. Southwesterly winds
increase around 15 mph through the afternoon. A weaker lead trough
progresses over the northern plains Sunday morning, bringing a
chance for light drizzle. Freezing precip should not be a concern as
guidance is trending warmer near 40 degrees for morning lows.
Precip chances increase Sunday evening into Monday as the system
shifts east over the northern plains. Discrepancies remain on
guidance as the latest ECMWF is less amplified and impacting more
of the eastern CWA, similar to the GEM. In addition, the GFS is
more amplified from an upper jet streak rounding the southern edge
of the wave. Given this and the amount of saturation is relative
compared to previous systems, will continue with 30-40 pops until
more consistency is seen between runs. Bulk of the QPF is rain on
Monday as highs peak in the upper 40s. The freezing temps slide in
behind the departing wave where a rain and snow mix is possible
Monday evening. No accumulation is expected at this time.

An anomalous upper ridge builds eastward into the region Tuesday and
Wednesday giving the area a chance to clear out the stratus clouds.
Modified airmass in the wake of the system will only drop highs into
the low 40s for highs and lows in the upper 20s and low 30s. In
terms of Christmas Day, much uncertainty exists with the timing and
track of the next upper trough. Latest runs are trending slower with
the system, GFS being more progressive and impacting mainly north
central areas. Meanwhile the ECMWF is slower and places our area in
the dry slot. While confidence is below average, will maintain
forecast consistency with slight chances for a rain and snow mix.

&&

.AVIATION...(For the 12Z TAFs through 12Z Saturday Morning)
Issued at 518 AM CST FRI DEC 19 2014

Uncertainty hings mainly on what the CIGS will do. Have continued
with the prev forecast idea of CIGS gradually improving above 1
KFT this afternoon. Have timed this with the passage of the
surface ridge axis, thinking southerly winds around 5KT could aid
in boundary layer mixing and cause the CIGS to lift. Since none of
the forecast soundings mix out the low level inversion this
afternoon, think IFR CIGS are likely to return overnight.

&&

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

&&

$$

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





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