Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 200609

Area Forecast Discussion
National Weather Service Topeka KS
1209 AM CST Tue Feb 20 2018

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Tuesday)
Issued at 305 PM CST Mon Feb 19 2018

An upper level trough across the southwestern US will lift
northeast across the central plains on Tuesday. The surface
cold continued to push southeastward across southeast KS
into southwest MO. As the upper level trough begins to lift
out into the central and southern high plains Tonight, a lee
side surface low will deepen across southeast CO. This will
cause the front across extreme southeast KS and southwest MO
to become stationary and even lift northwest towards the
southeast counties of the CWA, so temperatures across areas to the
south of I-35 may warm into the 40s and even some 50 degree
temperatures across Anderson CO. Meanwhile the shallow cold
airmass across the central and western counties of the CWA will
only modify slightly and temperatures will remain in the upper 20s
to lower 30s. As 850mb winds back more to the south, we`ll see
deeper 850mb moisture advect north-northeast across the CWA. The
resulting isentropic lift and large scale ascent ahead of the H5
trough will cause rain and perhaps some elevated thunderstorms to
develop across south central KS, then expand northeast across the
eastern half of the CWA through the night. Areas at or below
freezing may see periods of freezing rain Toning, generally along
and west of a Holton to Council Grove line. The far northwest
counties may only see freezing drizzle as the ascent and moisture
may stay just east of the western counties of the CWA. I think
much of east central KS will see temperatures warm into the upper
30s north of I-35, which should keep precip in the form of rain
for TOP, LWC, and EMP. There may be enough instability for
elevated thunderstorms to develop along and southeast of the KS
turnpike Tonight.

Through the early morning hours the stronger ascent will shift
northeast and a surface low will develop across southern MN in
the vicinity of the left exit regions of the 90KT H5 jet max.
This will result in stronger CAA across SD and NE and bring a
strong push of arctic air southeast across the CWA during the
morning hours. The 12Z NAM is much colder with temperatures than
the other numerical models and would keep freezing rain going
through the night for areas along and northwest of the KS
turnpike. Other models modify the shallow cold airmass across the
CWA this afternoon and slowly warms all of east central KS above
freezing through the evening hours and into the night before the
stronger CAA shifts southeast across the CWA from 12Z through 18Z.
The NAM, RAP and ARW show temperatures dropping below freezing
along and west Oskaloosa, to Topeka, to Emporia line by 12Z TUE.
This area may also see the steadier stratiform rain which may
produce up to 0.2" of ice accumulations from western Jefferson
County, northern and western Shawnee, Wabaunsee and northern and
western Lyon counties. This may occur right during the morning
rush hour, so I will expand the current winter weather advisory
east by one row of counties, then southward against the ICT CWA.
I`ll keep the time the same in case temperatures do not warm above
freezing, there is still some uncertainty in temperature trends
and QPF. If any elevated thunderstorms develop in the areas that
remain below freezing, then ice accumulations in some areas may be
higher than forecasted.

Tuesday, as the lead H5 trough lifts northwest across the plains
into the upper midwest. A longer wave length trough will continue
across the western US. The freezing rain will shift east into MO
during the late morning and early afternoon hours. There could be
some minor glaze of ice across the remainder of the east central
KS during the mid and late morning hours before the precip ends.
Highs on Tuesday will only reach the upper 20s across north
central KS with lower to mid 30s across much of the remainder of
the CWA. The southeast counties may have morning highs in the
upper 40s to around 50 before temperatures fall back into the 30s
during the afternoon hours.

.LONG TERM...(Tuesday night through Monday)
Issued at 305 PM CST Mon Feb 19 2018

Tuesday night through Thursday, another upper level trough will
dig southeast into the southwestern US and lift northeast across
the plains on Thursday. Ahead of the H5 trough deeper 850mb
moisture will advect northward across the CWA which will result in
another round of freezing rain. The vertical temperature may
start out cold enough across north central KS for snow but the
snow will transition to freezing rain as a warm nose advects
northeast between 850-700mb. We could see periods of freezing rain
or drizzle lasting through Noon on Thursday before the precip
ends. Lows Wednesday night will be in the teens and 20s. Highs
late Thursday afternoon will be in the lower 30s across north
central KS with mid to upper 30s across the remainder of the CWA.

Friday, we`ll see drier weather with highs reaching the lower to
mid 40s. A third upper level trough will dig southeast into the
southwestern US.

Friday night and Saturday, The upper trough across the southwestern
US will lift northeast into the plains Friday night into
Saturday. There could be another round of freezing rain changing
over to sleet and snow as the H5 trough axis lifts northeast
across KS on Saturday. The precip should end Friday afternoon and
High may reach into the 40s if we see some insolation.

Sunday through Monday, the mid to upper level flow will become
zonal. A lee surface trough will deepen across the high plains
which will cause surface winds to become southerly. High
temperatures will warm into the 50s.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1205 AM CST Tue Feb 20 2018

Thunder freezing rain storms with hail are moving across the taf
sites. As these storms move northeastward there could be a lull
with freezing drizzle. Another round of freezing rain is expected
towards sunrise which will last until late morning. LIFR/IFR
ceilings are expected until late morning when the ceilings start
to improve and possible lift to VFR or scatter out.


Winter Weather Advisory until noon CST today for KSZ009>012-



LONG TERM...Gargan
AVIATION...Sanders is the U.S. government's official web portal to all federal, state and local government web resources and services.