Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 172317

Area Forecast Discussion
National Weather Service Topeka KS
617 PM CDT Thu Aug 17 2017

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Friday)
Issued at 247 PM CDT Thu Aug 17 2017

Early afternoon water vapor imagery today depicted a progressive
synoptic pattern that will persist for tonight and into tomorrow
with a longwave trough over the central CONUS. One shortwave was
ejecting northeastward over the Great Lakes with a second impulse
digging southward along the upstream flank of the longwave.
Surface high pressure over southern Kansas will slide
southeastward this evening and facilitate southerly return flow
and theta-e advection across the High Plains. As the H500 wave
approaches, diurnal showers and storms along the Front Range are
expected to track eastward overnight, sustained by a 30 to 40 kt
LLJ. Model consensus in the timing and placement of these cells
has been less than ideal with even the 12Z GFS/EC showing breaks
in the their QPF fields and CAMs such as the HRRR/NSSL WRF/ARW/NMM
cores failing to bring widespread precip into the area prior to
sunrise. However, given the modest kinematic forcing, coupled with
1000 J/kg of MUCAPE in the RAP/NAM BUFR soundings and 20-40 kts
of deep shear, kept slight chance POPs across the western half of
the CWA through 10Z.

Some solutions hint at the redevelopment of precip over the Flint
Hills region around 12Z, possibly tied to the continued theta-e
advection on the nose of the LLJ. This elevated convection will
likely wane by late morning as the jet weakens. A dryline working
eastward with the complex will be the focus for peak heating
convection southeast of the Turnpike around 21Z tomorrow. MLCAPE
values of 1500-2000 J/kg coupled with 30-40 kts of deep shear would
support stronger storms, which could remain discrete given the
orientation of the mean flow perpendicular to the boundary. As with
yesterday`s complex, there are signals in the deterministic
solutions that initiation will be further east than previously
progged. Thus maintained only chance POPs across the SE for tomorrow

.LONG TERM...(Friday night through Thursday)
Issued at 247 PM CDT Thu Aug 17 2017

Convection ongoing late Friday afternoon continues to move
slightly faster eastward in model runs, with latest NAM depicting
more stout convection just east of the state line. Will carry
slight chance to low end chance and clearing after midnight.
Behind this wave, high pressure moves in for Saturday, and with
clear skies and sunshine may still reach near 90 although
dewpoints still hold in the 60s for one more day. A late night MCS
is progged to roll out of northwest Kansas or western Nebraska in
the LLJ regime for Sunday morning across the western counties,
but don`t anticipate it will make it across the east and have kept
PoPs out for the morning. Some discrepancies for Sunday afternoon
as flow aloft transitions to southwesterly and both GFS and EC
pepper low end QPF over the area, but think these chances are less

For the eclipse on Monday, uncertainty remains as to amount of
cloud cover and rain chances. GFS continues to generate overnight
convection across Nebraska along the warm front, then propagates
it east southeastward into Iowa and northern Missouri into the
early afternoon. Meanwhile mid and high level moisture continues
to stream northeast out of the Mexican plateau and desert
southwest, with mid level moisture coming northward off of the
Gulf. Whether this is enough for solid cloud decks or scattered
enough to see the sun will be the question. The EC is a little
farther north and east with the frontal convection, with a bigger
slug out of the southwest generally east of here out over the
high plains. Good news would be that there doesn`t appear to be a
large system over the area at the middle of the day, and the devil
will be in the details for cloud cover.

Front does appear to get pushed back southward through Tuesday as
we return once again to a northwesterly flow pattern over the
central states and a trof to our east. This would keep highs in
the 80s and potentially bring the dewpoints back down mid to late


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 614 PM CDT Thu Aug 17 2017

VFR conditions are expected through the period. Have kept the
mention for VCSH near 13-14Z for sites, although confidence in
this activity is decreasing. Will need to assess this potential in
next TAF issuance as convection continues to be monitored through
the evening.




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