Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 231756
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
1256 PM CDT SAT APR 23 2016

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 305 AM CDT SAT APR 23 2016

07Z water vapor imagery shows an upper trough over the intermountain
west with an upper ridge over the Great Plains. At the surface, low
pressure in the lee of the central Rockies continues to gradually
deepen and a surface ridge axis stretched from the southern plains
to the upper Midwest.

For today there does not appear to be much in the way of forcing for
precip as the upper ridge remains over the area. Models do show some
weak theta-e advection in mid levels and some short range models
develop some hit or miss showers through sunrise over north central
KS. Although forecast soundings are rather modest with any mid level
moisture advection. Because of this think chances for measurable
precip are to low to include in the forecast. The pressure gradient
is progged to increase through the day today as the lee trough
continues to strengthen and move east into the plains. This should
lead to south winds gusting between 25 and 35 MPH today. Models also
show the thermal ridge setting up within the surface trough. So
highs in the upper 70s to around 80 appear to be on track as models
mix the boundary layer to around 850MB and warmer air setting up
just to the west of the forecast area.

By tonight the upper trough is progged to move across the central
Rockies to the northwest of the forecast area with increasing large
scale forcing moving into the central plains. The strongest dynamics
look to remain to the northwest of the forecast area. However there
are signs of increased vertical motion across north central KS along
with increasing moisture. Models continue to show the potential for
elevated showers and thunderstorm development before dawn across
north central KS as mid level lapse rates steepen up to around 7
C/km. There does not appear to be any obvious speed convergence
along the low level jet so have kept a chance POP at this point.
Lows should be somewhat warmer tonight due to increased mixing of
the boundary layer as well as mid level clouds increasing from the
west. So lows are forecast to be in the upper 50s and around 60.

.LONG TERM...(Sunday through Friday)
Issued at 305 AM CDT SAT APR 23 2016

Main focus in the extended remains the potential for severe weather
Sunday afternoon and again on Tuesday afternoon. Any residual
activity by Sunday morning should be focused over north central
Kansas, lifting east and dissipating as brief mid lvl subsidence
builds in behind the shortwave trough. Models remain in pretty
similar agreement with the setup of the dryline/Pacific Front over
central Kansas by 18Z Sunday. Sided closer to the GFS and Ecmwf
solutions in the official forecast as the NAM has been the outlier
with the upper low centered further north than consensus. A lead
vort max ahead of the parent trough is progged to shift eastward
over the CWA, while decent low level convergence develops
along/ahead of the dryline over central KS. Dewpoints near 60
degrees with highs in the upper 70s signal mixed layer cape values
in the 1500 to 2000 J/KG range. Effective shear values are overall
in the 40 to 45 kt range, sufficient for supercells to develop in
the late afternoon and early evening time period. Initially,
discrete updrafts are likely with the main hazards being large hail.
After 7 PM, low level jet veers winds towards the southwest,
enhancing the 0-1 KM bulk shear to 30 kts while LCL heights are
fairly low. If storm mode remains as discrete supercells in the
early evening hours, large hail, damaging winds, and tornadoes would
be possible. The more likely scenario is for cells to quickly
congeal into a line as they quickly race east through the area,
becoming primarily a wind threat. Precip should come to an end
overnight with the frontal boundary laying up from west to east over
southern Kansas. For Monday evening, kept a low end chance mention
for thunderstorms with the ECMWF and NAM guidance lifting the warm
front into the southern half of the CWA. A few isolated severe
storms may be possible during this time, being a large hail and
damaging wind threat.

For Tuesday`s system, in addition to the subtle differences in
guidance, main change to the ECMWF has shown trends of slowing and
more in line with the GFS with the upper trough over northern New
Mexico by 00Z Wednesday. This would also slow the upper forcing to
not arrive in northeast Kansas until the evening hours. The ECMWF
and GFS are still persistent in their own respects of the warm front
location, but are showing similar signals of precip focusing within
the warm sector towards south central KS at 00Z Wednesday. This
activity would lift northeast into our area through the evening as
the upper low phases and lifts northeast with the sfc low across
Kansas. All severe weather hazards are a possibility with these
storms as this setup still favors discrete supercells in the area.

The speed of the upper low exiting differs between guidance on
Wednesday with the possibility of showers and isolated thunderstorms
lingering into Wednesday afternoon towards the Nebraska border and
far eastern Kansas. Depending on how quickly the dryline moves
eastward by late afternoon, additional severe convection is possible
just east of the area in western MO. Thursday is the coolest day of
the week with readings in the upper 60s before the next upper low
dives southward towards the southwest CONUS before lifting northeast
into the plains Friday and Saturday. The system itself does not
appear as organized at this time however there is a chance for
seeing severe weather in this period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
Issued at 1239 PM CDT SAT APR 23 2016

For the 18z TAFs, winds will continue to be strong from the SSE
and gradually veer more southerly into the evening. An upper
trough continues to advance into the region overnight which could
bring about LLWS conditions. With boundary layer winds not
expected to calm too much tonight, have left out LLWS in the TAFs
for now. This will be something to monitor though and if winds do
calm then LLWS could be a concern from around 6Z to 13Z time
frames. Near KMHK there could be some morning elevated TS and have
handled this with VCTS for now as more widespread TS activity is
likely to hold off until Sunday afternoon.

&&

.TOP Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...Wolters
LONG TERM...Bowen
AVIATION...Drake



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