Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 212129
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
329 PM CST Wed Feb 21 2018

.SHORT TERM...(This evening through Thursday Night)
Issued at 328 PM CST Wed Feb 21 2018

A challenging and impactful weather system is in store for tonight
through Thursday evening, bringing a wintry mix of precipitation and
snow/ice accumulations across the entire outlook area.

This afternoon a broad mid-level trough was stretched across the
western U.S., and this trough will remain anchored there through
Thursday night. An embedded shortwave over the Texas panhandle will
continue to lift northeastward into Kansas tonight into Thursday
morning.  Increasing cloud cover has been streaming northward over
the area ahead of this advancing wave, which has kept temperatures
in the 20s this afternoon. As of 21Z, some light radar returns were
extending into central KS. These returns are associated with
increasing mid-level moisture advancing into the area, however model
soundings show we still have some low-level dry air to overcome.

Models show deeper saturation and increasing lift by early this
evening across portions of central to east central KS as that
shortwave approaches the area. As this deep layer of moisture and
lift spreads northward across the CWA, have PoPs quickly increasing
this evening with widespread precipitation expected through the
overnight hours into Thursday morning.  Model soundings are showing
plenty of lift and deeper moisture extending into the dendritic
growth zone this evening, thus supporting precipitation initially in
the form of snow.  However, as we progress through the evening
hours, the warm nose looks to become warmer and may be present over
a deeper layer. As a result, areas of snow will likely transition
over to and/or mix with sleet across central to east central KS this
evening, lifting northward to around the I-70 corridor between 10pm
and midnight. The next challenge with transitioning precipitation
types comes overnight through sunrise as we start to lose saturation
in the dendritic growth zone from south to north across the CWA.  As
a result, the areas of snow/sleet will likely transition over to
freezing rain and eventually freezing drizzle as we continue to lose
more mid-level moisture.  High temperatures for Thursday will be a
bit tricky as some locations across east central KS may rise above
freezing during the afternoon (with highs into the mid and possibly
even upper 30s).  While the amount of moisture and lift will be the
lowest during the afternoon hours, it still may be sufficient enough
to keep areas of freezing drizzle and drizzle/rain (in east central
KS) through the afternoon and early evening hours before this system
finally exits to the northeast.  So depending upon how far north
above-freezing temperatures extend during the afternoon hours, it
will have an impact on where that cut-off will be between freezing
drizzle and drizzle.  Models show slightly more lift late afternoon
into early evening as another weak shortwave quickly tracks over the
area.  As a result, have areas of drizzle/freezing drizzle
continuing into the evening hours and drying out from west to east
across the CWA by midnight. With regards to precipitation totals,
most locations should receive at least 0.10" of snow/sleet, with a
zone of 1-2 inches possibly extending from central KS into northeast
KS. With the freezing rain potential overspreading the entire CWA,
most locations may receive around 0.10" of ice accumulation, with
upwards of 0.20" to 0.25" ice accumulations into east central KS.

Surface high pressure will move into the region behind this exiting
system on Friday, keeping conditions dry during the daytime hours
with afternoon highs reaching into the low/mid 40s.

.LONG TERM...(Friday through Wednesday)
Issued at 328 PM CST Wed Feb 21 2018

A brief break in precipitation will be seen Friday before chances
for a wintery mix return Friday night as the mid-level trough swings
across the central Plains Friday night through Saturday night. The
GFS and NAM seem to be in decent agreement with the timing of this
system, with the best chances for precipitation late Friday night,
and moving out of the area by midnight Saturday.  Soundings indicate
things may start off as as drizzle and freezing drizzle through the
night, with better saturation of the column occurring after sunrise
transitioning drizzle over to rain or freezing rain. Fortunately on
Saturday, temperatures look to rise into the mid 40s in north
central Kansas and to the mid 50s in east central Kansas.  With
this, any frozen precipitation should transition over to rain by
the afternoon.  Added some slight chances for thunder in east
central Kansas as the GFS does show some weak instability in the
early afternoon.

Finally some calm weather is forecast from Sunday through Tuesday
with dry conditions expected as high pressure moves in Sunday.  Mild
temperatures are also forecast these days with highs in the 50s,
even reaching into the 60s by Tuesday.  More chances for
precipitation return Wednesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1142 AM CST Wed Feb 21 2018

For the 18z TAFs, a wintry mix of snow, sleet, and freezing rain
is expected this evening through Thursday morning across the TAF
sites. As this precipitation lifts northward toward the TAF sites
this evening, MVFR cigs/vis will overspread the area. There will
be the potential for some moderate precipitation at times, and if
that occurs over the TAF sites some periods of IFR visibilities
will be possible. As precipitation continues into the morning
hours, models show the cloud cover lowering to IFR conditions and
possibly even to LIFR conditions by the end of the TAF period.


&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon CST Thursday for KSZ008>012-
020>024-026-034>040-054>056-058-059.

&&

$$

SHORT TERM...Hennecke
LONG TERM...Heller
AVIATION...Hennecke



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