Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 302339

539 PM CST Fri Jan 30 2015

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Saturday)
Issued at 305 PM CST FRI JAN 30 2015

Water vapor imagery this afternoon depicts the main  southwest
upper trough rotating towards AZ while areas of vorticity maxima
and precipitation stretch further eastward towards CO and NM.
Across British Columbia, Canada, an additional shortwave trough
was tracking southeast, progged to impact our CWA later in the

In the meantime, focus turns to the areas of mid level moisture
increasing west to east as the upper trough slowly progresses
towards the central plains tonight. Observations combined with
short term guidance remain in agreement with areas of rain showers
lifting north and east, increasing in coverage and intensity by
sunrise Saturday. Onset of precip commences between sunset and
midnight tonight over north central Kansas where best chances for
accumulating rainfall are possible. After midnight, higher chances
spread towards east central KS. Profilers show ice growth
occurring in the dendritic zone while gradually warming at or just
above freezing within the lowest 3 kft from the sfc. For this
reason, rain may mix with snow especially from midnight through
mid morning Saturday as lows drop between 31 and 33 degrees. Any
snowfall is not expected to accumulate with the warmer ground
temps in place. Best area for this scenario occurring is across
north central KS where slick spots may be possible on elevated
surfaces early Saturday morning.

On Saturday, boundary layer winds increase from the south,
lifting warmer air back into the area. Forecast highs between
guidance continued to trend in the upper 30s with a few locations
near 40 degrees during the late afternoon. Main precipitation
shield arrives during this time where high confidence lead to
adding definite precip chances for the entire CWA. Lift remains
persistent during this time as rainfall efficiency maximizes with
PWAT values at 3 standard deviations above the normal for this
time of year. Widespread light to moderate rainfall may reach half
of an inch by late afternoon before the next wave and colder air
arrives from the northwest.

.LONG TERM...(Saturday Night through Friday)
Issued at 305 PM CST FRI JAN 30 2015

Abundant moisture advection continues to stream across the
forecast area Saturday evening and into the overnight hours into
early Sunday. Temperatures across the northern counties drop from
middle 30s early evening toward the upper 20s by midnight, while
counties in the southeast are likely to remain above freezing for
much of these same hours. Will carry a rain/snow mix NC with rain
to the SE, and may see a light accumulation in the NC counties in
by around midnight.

Best chances for any snow to accumulate still come in the 06-12z
window as the strong cold air advection brings a quick drop in
temperatures across the western 2/3rds of the forecast area and
generally north of I70. By this time, QPF values in colder areas
are generally less than a tenth of an inch, while warmer areas
southeast that stay in the rain may pick up another quarter inch
of rainfall. Moisture becomes scant after 12z for much of the area
and will only carry some light accumulations as the cold air and
its high snow/liquid ratio with what remaining moisture there is
makes a quick sweep through the eastern half of the area by the
early afternoon hours. Highs may start out overnight in the 20s
and 30s but fall throughout the day as the cold front comes in.
Lows fall into the teens to single digits into Sunday night.

Its worth noting that for much of this rain/snow event that there
may be only a few hours where the sounding is cold enough to
support snow making it to the surface, and have kept accumulations
in the northern counties generally around 1.5 to 2 inches. Farther
south along the interstate may see half an inch to an inch, but
for the most part the column remains too warm early on, then dries
out too quickly, to accumulate much in the southern areas.

Monday southerly winds make a return late in the day along with
some increase in cloud cover and should get high temperatures back
into the lower 30s. Nice recovery day on Tuesday as once again
another thermal trof sets up across our area ahead of the next
cold front, and mixes highs back up into the 50s. Strong front
comes in Tuesday night into Wednesday and may bring light snow or
a rain snow mix through as it passes. Highs currently forecast in
the 30s to low 40s but may end up lower if front comes south
faster as EC would suggest . Overnight lows forecast in the
teens, with highs on Thursday near 30 as colder high slides east,
warming to around 40 /near normal/ on Friday.


.AVIATION...(For the 00Z TAFs through 00Z Saturday Evening)
Issued at 539 PM CST FRI JAN 30 2015

VFR conditions are expected to transition to MVFR cigs and vsbys
after 08Z with IFR cigs developing in the 15Z to 18Z time period.
Also expect initial vsbys to be VFR with the -RASN and then lower
to MVFR from 11Z through the end of the period with -SHRA.




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