Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 010825
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
325 AM CDT TUE SEP 1 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 322 AM CDT TUE SEP 1 2015

A broad upper ridge extended from the southwest US, east-northeast
across the southern plans into the southern Great Lakes States. An
upper level trough was amplifying across the Pacific Northwest. IR
satellite imagery showed a band of mid-level moisture extending from
western Mexico, north-northeast across the NM into the central high
plains then northeast into the upper midwest along the western
periphery of the upper level ridge axis.

Early this morning a weak upper trough was lifting northeast across
northwest KS. The weak ascent combined with weak isentropic lift was
causing some elevated showers and thunderstorms from northwest KS
northward into western NE. The HRRR tries to move some elevated
showers towards north central KS this morning. However, as the
boundary layer mixes the isentropic lift should weaken enough that
these showers should dissipate.

The ARW run of the WRF model shows the weak H5 trough across
northwest KS slowly tracking east-northeast across north central KS
and central NE this afternoon. The ARW does show a few elevated
showers or storms developing across Republic and Cloud counties
after 21Z. I kept a 14 pop in for the far northwest counties in case
the ARW solution were to verify. Most of the area will see mostly
sunny skies though the mid-level moisture plume may shift east into
the western counties of the CWA which would increase the high and
mid level cloud cover this afternoon. Highs across north central KS
may only reach near 90 degrees with lower to mid 90s across the
remainder of the CWA.

Tonight, The NAM and GFS show a second minor H5 trough lifting
northeast across northwest KS into central NE, around periphery of
the broad upper ridge axis. Both models show some isentropic lift
developing after 3Z across the northern counties of the CWA and
combined with weak ascent ahead of the H5 trough there could be a few
elevated showers or thunderstorms. Forecast soundings show bases may
be around 10,000 feet with some weak upglide at the 310 theta
surface. An increasing LLJ may also help to provide some ascent for
parcels to reach their LFC during the late evening and early morning
hours of Wednesday across the western and northern counties of the
CWA.

Both the ARW and NMM WRF model solutions show no QPF developing
Tonight with the better ascent and isentropic lift shifting
northward across central NE. Due to the model solution discrepancies
I will only go with slight chance pops tonight for the western and
northern counties of the CWA. The best chances for elevated showers
and storms will be along the NE border. overnight lows will be
around 70.

.LONG TERM...(Wednesday THROUGH Monday)
ISSUED AT 322 AM CDT TUE SEP 1 2015

On Wednesday morning there will still be a slight chance of a
lingering shower or storm in north central KS as the mid-level
shortwave continues to track eastward over southern NE and northern
KS. Isentropic lift appears to be rather weak during this period,
but there may be additional lift from a weakening low-level jet that
veers over that area in the morning hours. Soundings show dry air in
the lower levels, which could enhance the downward momentum transfer
of the the low-level jet to the surface through evaporation. These
wind gusts would be sub-severe since the jet speeds are less than 40
mph. The remainder of the day should be dry with general subsidence
behind the departing shortwave. The surface pressure gradient is
forecast to increase across eastern KS through out the day so expect
wind speeds around 15 to 25 mph with gusts up to 30 mph. On Thursday
morning models are depicting a similar scenario for north central KS
although it is hard to discern any obvious shortwave in the models,
and the isentropic lift appears weak again. The pressure gradient
remains strong across the region so expect similar windy conditions
during the day Thursday. The pattern is not forecast to change much
with southwest flow aloft locked in place until next weekend. Later
this week a strong mid/upper level system will track over the
Pacific NW and eventually the northern Rockies. Long term models
lift the remaining energy from this wave over the northern plains
sometime early next week given some timing differences. This should
send a cold front towards the area bringing the better chances for
showers and storms. The GFS is the fastest and further east with the
track of the wave therefore advancing the front quicker. There could
be a brief slight cool down behind the front before the mid/upper
ridge builds back over the plains.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z Tuesday NIGHT)
ISSUED AT 1148 PM CDT MON AUG 31 2015

VFR conditions are expected through the period. Lower boundary
layer will remain mixed through sunrise so not expecting any
mist to form. Surface winds should average around 8kts through 14Z
with a gradual increase above the surface so not including any
LLWS at this time as low level jet will be stronger west of the
terminals. Winds increase to around 12kts by 16Z with gusts to
22kts, then decrease to around 8 kts after 00Z.


&&

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

$$

SHORT TERM...Gargan
LONG TERM...Sanders
AVIATION...53


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