Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 172330

630 PM CDT Fri Apr 17 2015

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Saturday)
Issued at 346 PM CDT FRI APR 17 2015

Upper low continues to spin over the Rockies this afternoon with an
upper level jet rounding the base of the upper low and moving over
New Mexico. Earlier showers and thunderstorms were moving out of the
northern counties at 20Z. Some clearing was occurring across the
southern and western sections of the cwa this afternoon. Latest meso
analysis shows surface based CAPE around 500 to 1000 J/kg with an
uncapped atmosphere. Expect scattered convection to develop in
southwest Kansas along the dry line. additional scattered storms may
develop in south west and south central Kansas per the latest runs
of the RAP and HRRR. Models suggest additional development this
evening across western and central Kansas moving northeast into
north central Kansas with the increase and veering of the low level
jet overnight. Models are in agreement with a lobe of energy working
it`s way northeast out of Oklahoma later tonight and Saturday
morning. May see a repeat of this morning with an area of showers
and embedded thunderstorms moving across the area. Expect a break
for a few hours in the afternoon, then chances increase again with
storms developing again in the afternoon in western and central
Kansas as upward vertical motion increases with the advance of the
upper trough into the High Plains. Dryline looks to set up across
western Kansas with the GFS the furthest east in central Kansas.
Shear and instability will be favorable for some of the storms to be
strong to severe with large hail and winds the main hazards in the
late afternoon hours mainly west of a Herington to Washington

.LONG TERM...(Saturday Night through Friday)
Issued at 346 PM CDT FRI APR 17 2015

Short range models are relatively consistent in moving surface low
and main piece of upper trough through eastern KS late Saturday
night and Sunday.  Ahead of this system Saturday night, increasing
thunderstorm chances are expected, with some potential for severe
weather, with the best chance in our forecast area over the  western
2/3.  Shear parameters are not very impressive and amount of
sunshine and associated surface heating Sat afternoon and evening is
also a little suspect so this is not a high probability thing.

As the low and front move through on Sunday, some isolated thunder
may continue in the east in the morning, but showers associated with
cold air aloft just behind the front will continue precip chances
into the afternoon hours.

After that, subsidence and cold advection behind that system brings
in dry conditions and cooler temperatures for Sunday night through
Tuesday, with lows dipping into the upper 30s many places and highs
in the low to mid 60s.

Precip chances return to parts of eastern KS on Wednesday when weak
low-level warm advection and a weak wave in northwest flow aloft
interact. Latest ECMWF and GEM would indicate that the cool air at
the surface is more entrenched in place than the GFS, thus have
gone cooler than guidance for highs on Wednesday.

Beyond Wednesday, considerable differences exist between 12Z GFS and
ECMWF in upper flow pattern and precip chances.  GFS and GFSEnsemble
places us in a more favorable pattern for a couple days of precip
for Thursday and Friday, while the ECMWF is slower in bringing a
shortwave trough out of the southwest U.S., and would give us the
better chances on Friday. Have gone with a general compromise
with 25 to 40 percent POPs for those days.


.AVIATION...(For the 00Z TAFs through 00Z Saturday Evening)
Issued at 625 PM CDT FRI APR 17 2015

VFR prevails through at least the first 6 hours of the forecast
period. Activity forming across western and southern Kansas is
expected to impact sites after 06Z. Forecast soundings denote
mostly showers with a few thunderstorms. After 09Z, coverage
increases across the area with rain saturating conditions to MVFR
through Saturday morning. Showers exit eastward as uncertainty
increases for the afternoon in timing of next round for thunderstorms.
Have a VCTS mention with improvement to VFR for the time being.




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