Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 230521
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1121 PM CST Thu Feb 22 2018

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Friday)
Issued at 330 PM CST Thu Feb 22 2018

Wintery precipitation has overspread the entirety of the forecast
area this afternoon as a shortwave lifts northeast across the
central Plains. A mix of freezing rain, freezing drizzle, and some
sleet have been the primary precipitation types with this system.
Temperatures have begun to warm in east central Kansas where
lingering precipitation this evening should transition over to
drizzle forced by isentropic ascent. Elsewhere (mainly areas north
of I-35) will continue to see freezing temperatures and
lingering, patchy freezing drizzle through late evening. Overall,
ice accumulations tonight should be minor with a Winter Weather
Advisory still in place for far northeastern Kansas where
additional accumulations up to one tenth of an inch may be seen.

The low clouds stick around tonight regulating low temperatures
overnight, which fall into the 20s and low 30s. Soundings indicate
the potential for some lower visibilities at the surface tonight,
so have opted to include some patchy fog until sunrise. As for
tomorrow, dry conditions are finally forecast during the day as
high pressure moves into the area behind the departing system.
Clouds will begin to clear from the northeast, although parts of
east central Kansas will stay overcast with clouds returning ahead
of the next system. Temperatures tomorrow will reach into the
40s.

.LONG TERM...(Friday night through Thursday)
Issued at 330 PM CST Thu Feb 22 2018

Focus on the longer term will be on yet another round of freezing
drizzle/rain early Saturday morning across portions of NE Kansas.

The longwave trough that has been the culprit for our multiple
rounds of wintry precipitation finally ejects from the Pacific NW
Friday night into Saturday morning. Surface high pressure slides
through during the daytime on Friday, but height falls ahead of the
approaching upper trough and lee cyclogenesis along the Front Range
lifts a stalled ARK-LA-TEX frontal boundary northward as a warm
front late Friday afternoon. Increasing 285-295K isentropic ascent
over the warm front coupled with strong low-level moisture advection
will fuel widespread light precip/drizzle Friday night into
Saturday. Forecast soundings from the GFS/NAM show another classic
FZDZ setup with all of the moisture confined in the warm nose and no
ice introduction aloft, coupled with surface wet bulbs in the upper
20s to around 30.

The depth of the moisture is high enough that some areas could
see FZRA, though the latest omega time-height plots are not all
that supportive of higher precip rates. Most, if not all, of the
Fg forcing will be south of the CWA, which will also keep QPF
amounts on the lower side. Precip looks to start SE of the
Turnpike before midnight on Friday night, spreading northward and
persisting through the day on Saturday. Increasing WAA in the BL
will change the precip type over to rain throughout all of NE Kansas
by 18Z Saturday. Some light snow is possible near the KS/NE border
before sundown on Saturday as increasing CAA behind the departing
cyclone cools the column below freezing. In east central Kansas, one
cannot rule out a stray elevated thunderstorm near the triple point
Saturday midday with the NAM in particular showing 300-400 J/kg of
MUCAPE above the warm nose prior to the passage of the cold front.

After this system departs on Saturday evening, little sensible
weather is forecast until mid-week. Surface high pressure builds
to the south as a more zonal upper level flow sets in. Increasing
H850 downslope flow Monday and Tuesday will push temperatures into
the 50s to low 60s. Confidence in the timing and characteristics
of the next system mid-week is on the low side with a modest
spread amongst the longer range guidance on the longwave pattern,
though there is some consensus on a blocking pattern setting up
towards the end of the week and next weekend, which would bring
dry weather and moderate temperatures to the region.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1114 PM CST Thu Feb 22 2018

IFR/LIFR ceilings are expected through late morning. There is
more uncertainty with the visibility although the chances for
dense fog appear low at this point. Models are showing slightly
drier air advecting southward and possibly just enough mixing in
the boundary layer to prevent dense fog. MVFR visibilities are
more likely. Late tomorrow morning the conditions look to improve
although the timing may need adjusting. As another system
approaches from the southwest ceiling begin to fill back in and
lower late in the period.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until midnight CST tonight for
KSZ008>012-020>024-034>038.

&&

$$

SHORT TERM...Heller
LONG TERM...Skow
AVIATION...Sanders


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