Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 160847
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
347 AM CDT Wed Aug 16 2017

.SHORT TERM...(Today and tonight)
Issued at 347 AM CDT Wed Aug 16 2017

A mid level trough axis currently stretches from CO to ND and is
responsible for a cold front advancing southward through NE and
western KS this morning. Widespread convection developed along the
front last evening, which has evolved into a large scale MCS. The
mucape ahead of the MCS is around 2000 j/kg and a strong low level
jet has set up over central KS. A well established cold pool is also
supporting the eastward progression. An additional area of
isentropic lift and moisture convergence is aiding storm development
across southeast KS. This area of lift is expected to move
northeastward over eastern KS this morning, and storm coverage
should expand over the next few hours. The HRRR is resolving the
current MCS and shows it somewhat maintaining strength as it moves
across the forecast area through the remainder of the morning. Also,
the low level jet is expected to veer during the late morning hours,
which could continue supporting new convection above the cold pool.
Other 00z CAMs did not resolve the convection as well therefore are
struggling with the current trends. Brief periods of moderate rain
and gusty winds will be possible as the storms pass through
especially in north central KS.

The main question for today will be how much precipitation and cloud
cover lingers across the area before the front pushes through. As of
now a majority of the models are hinting at some clearing in the
early afternoon allowing for the environment to destabilize ahead of
the front. If an MCV from the current MCS were to move over eastern
KS the timing could be such that subsidence behind the wave could
aid in clearing skies. With the lower to mid 70s dew points in place
and modest mid level lapse rates mucape is forecasted to reach 2,500-
3,000 j/kg. With the mid level trough progressing over the plains
expect deep layer shear around 30-35 kt. This mid level trough could
also provide the lift along with the front needed to break any cap
in place. Model consensus for storm development would be around 3-5
pm mainly along a line from Abilene to Marysville. Initially the
storms may be discrete and supercellular, but given the deep layer
shear vector is parallel to the front storms will likely evolve into
a linear complex. Large hail will be the a threat early in storm
evolution, but damaging wind gusts will be the primary threat
through the late afternoon and evening. The threat for severe storms
seems to be supported by the WRF ensembles and HRRR time lagged
probabilities for decent updraft helicity, and 10 m gusts greater
that 50 kt. The low level directional shear is marginal at best so
the tornado threat is rather low as compared to the backed flow
across IA closer to the low pressure. Sufficient moisture will lead
to pwats approaching 2 inches so heavy rainfall will be possible
with these storms, with the better chances across the southeastern
half of the forecast area. Storms should depart the area between 10
pm and 1 am as the front advances eastward.

.LONG TERM...(Thursday through Tuesday)
Issued at 347 AM CDT Wed Aug 16 2017

Thursday surface high pressure will move into northeast Kansas
behind the cold front through the day. Expect mostly sunny skies as
residual clouds move out during the morning hours. Temperatures will
be below normal in the low to mid 80s. A ridge will be in place over
the northern Rockies with northwest flow across the Plains. Another
upper level wave will move southeast Thursday night and Friday
across the northern Plains and into the Great Lakes to the middle
Mississippi Valley by 12Z Saturday. This system will bring the next
round of showers and thunderstorms to the area as a warm front lifts
northeast by early Friday morning. Best forcing will be from
northeast Kansas northeast into Iowa Friday night. An upper level
ridge builds into the central Plains Saturday allowing the area to
dry out through Sunday. Sunday night into Monday return flow sets up
across western and central Kansas into Nebraska. Mid level
shortwaves move eastward through the Plains with models differing on
the placement with some solutions north across the northern Plains
with others further south across Nebraska. Main takeaway is that
there will be a small chance for showers and thunderstorms Sunday
night and early Monday morning. A frontal boundary is forecast to
move into southern Nebraska or northern Kansas Monday night into
Tuesday morning. Good moisture transport is forecast Monday night
into Tuesday ahead of the front and attendant waves moving through
the Central Plains.

.Solar Eclipse for Monday, August 21st...

Latest model guidance indicates that there is uncertainty with the
timing and placement of precipitation across northern Kansas and
southern Nebraska Sunday night into Monday. That said, there remains
a slight chance of precipitation for the area. Some drying is
forecast into the early afternoon hours behind departing wave with
decreasing cloud cover. Model fluctuations and changes to the
forecast will continue through the week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1149 PM CDT Tue Aug 15 2017

Isolated to scattered storms through the early morning hours may
become more widespread by 10Z and continue through 15Z. There may
be MVFR ceilings and visibilities with any thunderstorms. We may
see a breaks in the overcast through the late morning and early
afternoon hours. A line of thunderstorms may develop across the
terminals this afternoon and last into the early evening hours
along a surface front. Winds will switch to the northwest behind
the front.


&&

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

$$

SHORT TERM...Sanders
LONG TERM...53
AVIATION...Gargan



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