Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 270456

Area Forecast Discussion
National Weather Service Topeka KS
1156 PM CDT Wed Jul 26 2017

Issued at 700 PM CDT Wed Jul 26 2017

The precip forecast remain a challenge for the evening and
overnight hours with very transient convective trends ongoing
across the central and eastern CWA. Both fine and broad-scale
guidance solutions been struggling to handle this forecast. Have
fine-tuned POPs/QPF values with this latest update to hit on the
new thunderstorm development along a convergence zone from
Washington to Jackson counties that is slowly propagating
eastward. Satellite trends in the SW CWA have shown little in the
way of agitation in the cloud shield, so haver trimmed back POPs
at least for the next few hours.


...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Thursday)
Issued at 335 PM CDT Wed Jul 26 2017

As of 20z, a pair of MCVs were traversing the CWA. The first was
virtually overhead of TOP, while the second was very near MHK. These
should allow moderate to heavy rainfall to continue along the
Interstate 70 corridor through the early evening hours. The
lingering showers and isolated thunderstorms have tempered
temperatures significantly this afternoon, only allowing temperatures
to reach the lower 80s. The much awaited cold front was situated
near Hays, KS northeastward to just south Omaha, NE. Mid and upper
level continues to remain zonal with weak embedded shortwaves,
contributing to enhanced lift for the ongoing convection.

For rest of the afternoon and evening hours: The ongoing
precipitation will exit the area near dusk. 12z KTOP sounding
observed 1.76 inches of PWAT, which has contributed to rainfall
rates as high as 1 to 1.5 inch per hour rates. Question marks still
arise for further development along the synoptic front. Scattered
showers and thunderstorms are developing along the front in portions
of east central and southeast NE. Given the environment to the south
has been turned over, the likelihood of storms maintaining through
the area is unlikely. That being said, the synoptic front is
expected to take more of an east to west orientation across far
northeast KS into northeast MO. A strong LLJ ~40 knots overnight
will provide lift for showers and thunderstorms, however the better
chances look to stay northeast of CWA. Given the cloud shield
overhead, temperatures are expected to remain mainly status quo
overnight with lows in the 70s. Any lingering shower activity will
exit by mid morning with high temperatures reaching the mid 80s
Thursday afternoon.

.LONG TERM...(Thursday night through Wednesday)
Issued at 335 PM CDT Wed Jul 26 2017

Mid and extended forecast remain with inherent uncertainties.  Upper
ridge remains anchored over the western CONUS into the Plains region
with a broad trough in the east.  Mean Westerlies generally reside
north near the Canadian border.  Monsoonal moisture remains over the
Desert Southwest into portions of the Rockies.  A couple periods of
small rain chances may prove to be the biggest challenge weather
wise mainly over western portions of the forecast area toward
north central KS. Overall confidence remains low in any case of
precip in the extended period as GFS/EC guidance keeps a mainly
dry atmosphere in place with little in the way of forcing with
semi-permanent surface ridge in place over northeastern and east
central KS. The Canadian model is really still the bullish
guidance responsible for any small precip chances at this point.
Have only kept mention of showers at this point due to atmospheric
sounding profiles suggesting rather warm mid levels in place with
weak lapse rates and rather disorganized and weak wind profiles.
With that being the case, any convection the models (mainly the
Canadian) develop and move east into the forecast area is likely
to develop over the upslope region of the Rockies and develop weak
convectively induced MCVs for the Sunday through Tuesday time
frames. General consensus is for these to weaken as they propagate
to the east probably remaining in the form of showers if they do
in fact make it into the forecast area. Eastward component to the
surface to H85 winds should tend to dry the region out a bit with
dewpoints in the lower 60s. This along with temps in the 80s will
result in more comfortable conditions heat- wise.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1153 PM CDT Wed Jul 26 2017

Showers and storms across portions of far eastern Kansas will
persist through the overnight hours with conditions falling to IFR
levels in the heavier rain. MVFR to IFR CIGS are expected to fill
in across the area overnight and persist through the morning
before lifting. Light winds tonight will become more established
from the north on Thursday.




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