Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 151158

558 AM CST Mon Dec 15 2014

...Near-term storm update and aviation forecast discussion

Issued at 552 AM CST MON DEC 15 2014

A quick note about the near-term forecast. The line of convection
in the northeast and eastern sections of the surface low is along
a strong axis of shear instability with SW winds gusting to 30 kts
behind the convection and SE winds around 15 kts ahead of it. This
seems to be allowing enhanced vorticity to develop along the
boundary and under the convective updrafts. Have seen a few
instances of small areas of rotation along this boundary, and
would not be surprised if weak funnel clouds developed in this
northeast sector of the low this morning. A brief weak tornado
seems VERY UNLIKELY at this point. Outside of these areas of weak
rotation, the strongest updrafts may produce brief periods of
small hail around the size of peas.


.SHORT TERM...(Today and Tonight)
Issued at 413 AM CST MON DEC 15 2014

Early Monday morning, the center of surface low pressure was located
about 20 miles northwest of Wichita, and forecast to move northeast
to around Topeka by 8 AM or so. The center of the upper low was
almost directly overhead the surface almost perfectly
vertically stacked system at the moment. A strong cold front also
extended from the surface low center north to near Concordia and
then to Lincoln Nebraska. This front has been surging southeast a
bit faster than models had forecast, and with colder post-frontal
temperatures by a few degrees. The freezing line was well northwest
of the forecast area, near Kearney Nebraska, but was making steady
progress to the southeast.

After an early morning lull in precipitation, showers and some
thunderstorms have been developing once again near and to the
northeast of the low pressure center. Given the very cold mid level
temperatures with this system, MUCAPE (and even some surface based
CAPE) up to 500 J/kg is present near, north, and east of the low.
There is a fair amount of effective bulk shear and helicity in the
eastern quadrant of the surface low, and will need to at least keep
an eye on storms through this morning for any signs of organization
or mesocyclone development, but instability is likely to weak for
any severe threat. If anything, small hail will be possible with the
strongest updrafts given the cold core system. In the northwest
quadrant of the low, where the majority of convective activity is at
this time, parcels are elevated above the surface front, and the
flow perpendicular to this front seems to have encouraged the
enhanced coverage in this zone. The storm system and convective
tendencies as a whole are expected to be more or less steady state
as the system shifts to the northeast and exits the area by mid to
late morning.

On the back edge of this storm system, sub-freezing temperatures are
expected to come near Republic county this morning but PROBABLY NOT
enter the county. A warm nose just above the surface is expected to
keep all precipitation falling as rain through at least 10 AM, so if
the temperature falls colder than expected there could be some very
light freezing rain in the far NW corner of the forecast area.
Again...this appears unlikely. Deeper cold air will build into the
area by late morning into the afternoon, and would support a mix
with or change over to snow from northwest to southeast by this
evening. While temperatures would support this change over,
precipitation is expected to come to an end over all but far
northern Kansas before this cooling can occur. Areas near the
Nebraska border in particular could see a period of snow showers
today with little to no accumulation expected.

.LONG TERM...(Tuesday through Sunday)
Issued at 413 AM CST MON DEC 15 2014

By Tuesday a weak mid-level ridge will begin to advance into the
central U.S. with surface high pressure centered over the region.
While this surface high will keep conditions dry through mid-week,
the northerly surface winds will continue to advect cooler air into
the region, resulting in high temperatures dropping into the 30s and
low temperatures Tuesday night plunging into the 20s and possible
even upper teens near the Kansas/Nebraska border.

Significant model differences continue to exist with the possible
mid to late week systems.  This first system of note is an embedded
shortwave that both the ECMWF and GEM show lifting northeastward
into the forecast area Wednesday evening through Thursday. The GFS
and NAM, in comparison, show this shortwave being significantly
weaker and staying further south, resulting in dry conditions across
the forecast area. Have trended more toward the ECMWF/GEM solution
but have kept only low-end chance PoPs in for Wednesday night and
Thursday due to the model discrepancies.  With low temperatures in
the 20s and highs on Thursday only reaching into the mid 30s, expect
most of this precipitation would be in the form of light snow. The
second system of note is associated with the mid-level trough that
is expected to move onshore mid week and progress eastward into the
Central and Southern Plains by late week. By Friday the models
differ with how far south across the Southern Plains this trough
will dig, resulting in notable differences in the track of the
mid-level low and associated surface low pressure system. Both the
ECMWF and GEM have trended further south with this system with the
mid-level low tracking across Arkansas and the surface low remaining
along the Gulf coast. This ECMWF/GEM solution would result in the
system entirely bypassing the forecast area and would keep
conditions dry late week. The GFS on the other hand has the
mid-level low tracking across the forecast area with the surface low
skimming across Oklahoma and Arkansas, resulting in some
precipitation across the area Thursday night through Friday night.
Have once again trended more toward the ECMWF/GEM solutions, however
have only trended down a bit with PoPs as this system is still
several days out and want to wait for more run-to-run consistency
before entirely removing PoPs from the forecast. If this more
southern solution materializes, it would usher more cooler air into
the region. Even with the GFS solution, high temperatures stay in
the 30s with lows into the 20s so much of the precipitation would be
in the form of snow with a rain/snow mix possible by the afternoon
hours on Friday.

The models do agree in a weak mid-level ridge and a large area of
surface high pressure building into the central U.S. by the weekend,
resulting in dry conditions and temperatures remaining steady with
highs in the 30s and lows in the 20s.


.AVIATION...(For the 12Z TAFs through 12Z Tuesday Morning)
Issued at 552 AM CST MON DEC 15 2014

The TAF is complex this AM as the surface low will track almost
directly over TOP and FOE, and just south of MHK. The result will
be frequent wind shifts early in the TAF along with frequent and
sometimes temporary changes in ceiling height. TS is also possible
through around 15Z or so. A cold front shifts winds out of the NW
with gusts 20-30 kts from late morning through the rest of the
TAF. This front is expected to bring cigs to IFR or low end MVFR
before gradually improving to around 2500 feet by late afternoon.
Expect these MVFR cigs to persist through the remainder of the TAF.




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