Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 162026

Area Forecast Discussion
National Weather Service Topeka KS
326 PM CDT Tue May 16 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 305 PM CDT Tue May 16 2017

Observational trends are on track this afternoon with a severe
weather event to occur across much of Kansas later this afternoon
and evening. Current visible satellite is showing towering cumulus
and first echoes developing over the Texas Panhandle. This is in
good agreement with short term models depicting around 4000 J/KG of
sfc CAPE in this region, stretching into south central KS with
minimal inhibition at the current hour. Dry line is entering
southwest KS and is expected to surge into western KS by 21Z today.
Convergence along and ahead of this boundary will likely trigger
more scattered convection in the late afternoon, quickly tracking
northeast and congealing into a bow echo mcs. Believe that the
capping inversion may weaken just enough over central and north
central areas for severe hazards to maximize in the 6 to 8 PM time
frame as the mcs enters north central Kansas. Low level shear and
subsequent helicity increases as you progress towards 00Z,
increasing the risk for an isolated tornado or two. If storm mode is
more of a cluster which is appearing likely, weak embedded tornadoes
along the leading edge of the line are possible. With a bowing line
segment, damaging winds in excess of 70 mph are going to be the
prominent hazard, along with large hail and heavy rainfall. Have
inserted categorical pops for north central KS after 7 PM, carrying
the mcs through much of the northern half of the CWA through 11 PM.
As the main upper trough lifts eastward, strong mid level lift and
decent instability within the region develops a secondary mcs,
lifting north and east into the CWA after midnight tonight. Given
the effective shear values increasing over 50 kts, may see a few
embedded severe storms within the cluster capable of damaging winds
and hail. The second MCS would likely impact the majority of the CWA
through Wednesday morning. Areas that experience both rounds of
convection may have a higher risk of flash flooding and river
flooding. Overall qpf totals average in the half to just over an
inch range.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 305 PM CDT Tue May 16 2017

The next several days each feature at least some element of severe
weather potential. From an overview perspective, Wednesday`s
weather will be driven by the movement of the strong negative tilt
trough northeast across eastern Nebraska while the trailing
dryline and front push east across the local area. The trajectory
of this system suggests that the unstable airmass will not be
pushed very far south of the area late Wednesday, and will return
into the area with a warm front on Thursday and advance of another
strong upper level low moving into western Colorado. A lead short
wave is well-predicted by all guidance to initiate widespread
storms late Thursday into Thursday night. Then by Friday into
Friday night the main upper trough makes a run across KS and NE
with the local environment likely to be in the unstable warm
sector, once again prompting a risk for severe storms. The
likelihood of multiple rounds of storms amidst strong moisture
influx over the period and occasional training potential suggests
that flooding (both river and flash) will be possible with the
threat potentially increasing over time as soils become
increasingly saturated. Details regarding each separate period of
severe weather potential follow:

Wednesday: On Wednesday, the main question will be the timing and
strength of low level forcing in conjunction with how well the
boundary layer instability recovers in the wake of overnight
storms. Upper level forcing with the incoming negative tilt trough
and cooling aloft will be pretty strong especially in northern KS.
Currently see potential for convective initiation in far northern
and far eastern KS by noon or shortly thereafter. There will be
ample shear and at least modest instability present so see some
potential for a few or a broken line of strong to severe storms to
develop with some supercell structures, but they may not mature
early enough to have an impact in the local forecast area before
moving off to the east. Regardless, will want to keep an eye on
this time frame given the strength of forcing and strong wind

Thursday: The warm front surges back north with instability
pooling near the boundary and a rather broad and conditionally
unstable warm sector. For now it appears that the warm sector will
remain capped for the majority of the day but CIN is not
particularly strong. Wind fields will strengthen throughout the
day as the upper trough approaches with ample deep shear available
by evening. The primary question on this day will be timing of
thunderstorm development once again as it could be another
instance where storms develop well to the southwest of the
forecast area and move this way through the evening hours. There
are also signals that inhibition does not become particularly
strong overnight as the lead upper short wave crosses the area so
could maintain a severe weather threat well into the night.
Supercell structures possibly morphing into broken line and bowing
segments should be expected.

Friday: Somewhat dependent on convective evolution and recovery
after Thursday night`s activity, see good potential for the
atmospheric instability to recharge during the day in advance of
the next strong upper wave. A broad warm sector can be expected
with moderate CAPE and strong wind fields including backed surface
winds. This is suggestive of the potential for supercell
structures including some tornado potential within the warm
sector...with the primary questions being how far north the warm
sector extends and how unstable it is able to become in the wake
of Thursday night convective overturning. For now, this is a
strong potential - low confidence forecast period.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1213 PM CDT Tue May 16 2017

VFR to start the forecast period as gusty south winds prevail
above 15 kts sustained through tomorrow. TSRA is expected to form
off the dryline and quickly race north and east into the area.
Initial, severe round is more likely to impact KMHK aft 01Z with
lesser confidence in TOP/FOE for this issuance so just have VCTS
mention. There may be a secondary round of TSRA that comes through
aft 06Z, clearing the terminals aft 14Z. Forecast soundings are
hinting at the potential for high end MVFR cigs aft 00Z this
evening, otherwise would not expect limiting categories with the
exception of being under TSRA.




LONG TERM...Barjenbruch
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