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000
FXUS63 KTOP 150843
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
343 AM CDT Fri Sep 15 2017

.SHORT TERM...(Today and tonight)
Issued at 304 AM CDT Fri Sep 15 2017

Early this morning a mid level shortwave trough was located over
northern Utah and Colorado moving northeast into Wyoming at 08Z.
Additional energy in the mid levels was moving northeast into the
Texas Panhandle and southwest Kansas. A cluster of showers and
thunderstorms was occurring over southwest and west central Nebraska
with isolated convection near Amarillo. Latest regional VWP from
radars shows 40 to 50 kt low level jet across western and central
Kansas into southern Nebraska at 08Z. the RUC and HRRR develop
scattered convection this morning prior to 12Z in the theta-e axis
and within the low level jet across central Kansas which would then
move northeast in north central and parts of northeast Kansas this
morning. Have adjusted precipitation chances and area for convection
through mid morning. Convection is expected to decrease as low level
jet weakens through the morning. Temperatures will be warm once
again with thermal axis extending into north central Kansas with
good mixing down from 800 mb yielding highs in the mid 90s. Further
east temperatures will warm into the upper 80s.

Tonight the upper level trough is forecast to move across the
Rockies as a cold front slides southeast and extends from southwest
Kansas to northeast Nebraska by 12Z Saturday. Boundary layer will
remain mixed tonight with winds remaining in the 10 to 20 mph range
with some higher gusts. COnvection is expected to develop within the
theta axis across northeast Kansas within the low level jet.
Elevated instability around 1000 J/kg of cape along with moderately
steep lapse rates are forecast along with 20 to 25 kts of shear.
Will continue with chances of thunderstorms after midnight with best
chances expected after 3 AM.

.LONG TERM...(Saturday through Thursday)
Issued at 304 AM CDT Fri Sep 15 2017

Strong southwesterly low level jet Saturday morning in advance of
the approaching upper wave and cold front will provide scattered
convection Saturday morning. Mid level lapse rates are decent with
the potential for perhaps a few strong wind gusts and small hail
with the taller updrafts. Convection should wane in the afternoon
as the front approaches. Strengthening sfc pressure gradient ahead
of the front increases wind speeds between 15 and 20 mph
sustained with gusts as high as 30 mph. Capping inversion weakens
in the late afternoon/early evening time frame within the warm
sector. Model guidance still varies somewhat on the exact position
of the approaching cold front with the NAM being the outlier and
faster solution. ECMWF appears more middle of the road with the
GFS being near the Nebraska border by 00Z Sunday. Regardless,
expect convection to fire along and behind the front during the
evening and overnight period. Both the NAM and GFS have MUCAPE
values in the 2000 to 3500 J/KG range while shear values are
sufficient in the 30- 35 kt range, backing towards the southwest
around 40 kts post frontal. Therefore a few marginally severe
storms are expected with hail and damaging winds being the primary
hazards.

Front lifts back northward as warm front through the day Sunday with
scattered thunderstorms redeveloping in the afternoon and evening
hours. GFS exhibits high instability near the boundary (in excess of
5000 J/KG of MUCAPE) while shear values are decent around 40 kts.
Depending on if the atmosphere is able to recover after the morning
convection, there could be another round of strong to severe storms
on Sunday. Temperatures were lowered a few degrees with latest
guidance showing more cloud cover and convection around with
readings generally in the upper 70 to low 80 range. As the frontal
boundary stalls somewhere in the Kansas to southern NE area,
continued the chance pop mention through Monday.

Temperatures recover back into the middle 80s through Wednesday
before an incoming Pac NW upper trough pushes another cold front
through the region Wednesday. Thunderstorms are once again possible
during this period with coverage and available moisture varied
between guidance. Another strong upper trough follows the previous
wave by mid week, with much variance on how it affects precip
chances and temps for Thursday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday)
Issued at 1141 PM CDT Thu Sep 14 2017

Not much change in forecast thinking. The HRRR/RAP/NAM continue to
show potential for elevated showers and storms, mainly west of TOP
and FOE. Profiler data is also showing 925MB winds increasing with
some risk for LLWS. So have not made any significant changes to
the prev forecast. In general VFR conditions should prevail with
surface winds becoming gusty during the day Friday as the
pressure gradient increases.


&&

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

$$

SHORT TERM...53
LONG TERM...Prieto
AVIATION...Wolters