Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 202346

Area Forecast Discussion
National Weather Service Topeka KS
646 PM CDT Tue Mar 20 2018

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Wednesday)
Issued at 330 PM CDT Tue Mar 20 2018

Clearer skies and warmer temperatures are forecast for tomorrow.

Afternoon upper-level water vapor imagery depicted a broad, low-
amplitude longwave trough centered across the CONUS with embedded
shortwaves propagating through the flow. One such wave was departing
the Central Plains while a second one was just upstream of the
region in the Dakotas and Nebraska. At the surface, an elongated
meridional ridge axis stretched from the eastern Dakotas to the
Texas Gulf coast. Widespread stratus has gradually broken down into
a more closed-cellular form this afternoon, but solar insolation has
been hindered enough to keep temperatures a few degrees lower than
originally forecast.

The backside of the stratus/stratocu has been slowly eroding over
the course of the day in north central KS and this trend is forecast
to continue for the remainder of the day and into tonight. The
combination of clearing skies, the passage of the surface ridge
axis, and antecedent moisture from rainfall yesterday will increase
the potential for fog development overnight. Plus, RH values will be
starting off higher owing to the dampening of today`s highs. High-
res guidance solutions vary widely on the potential for overnight
fog, but given the favorable synoptic setup, did insert patchy to
areas of fog into the forecast for tonight. The best potential for
fog will likely be confined to low-lying areas where decoupling and
moisture pooling are maximized.

The surface ridge pulls away Wednesday morning and allows return SSW
flow to become reestablished over the region. With the H850 ridge
axis not clearing the CWA until late in the day tomorrow, WAA will
not be terribly strong. H850 temps only rise from -1 to +4 C during
the course of the day. That being said, while many solutions have
backed down slightly on highs, leveraged the warmer BC grids for
highs tomorrow to account for the models` recent tendency to
under-forecast highs by several degrees on days with little cloud

.LONG TERM...(Wednesday night through Tuesday)
Issued at 330 PM CDT Tue Mar 20 2018

Multiple weather systems impact the region late in the week and
the weekend, with another round of warm weather between now and

Upper level ridging builds into the region for the remainder of the
week, pushing highs back into the 60s and 70s for Thursday and
Friday. A PV lobe makes landfall over the CA coast late Thursday and
ejects ENE into the Great Basin and the High Plains by late in the
day on Friday. A zonal band of baroclinicity increases eastward from
a developing Front Range lee cyclone--arching across much of the
Central Plains. Increasing 295-305K isentropic upglide and theta-E
advection may fuel elevated showers and storms Friday night along
this developing warm front, though forecast soundings from the
GFS show a stout cap in place and little in the way of elevated
CAPE. Furthermore, there remain modest differences between the
GEM/EC/GFS on the placement of the precip, which will be heavily
influenced on the exact low track.

This system quickly clears the forecast area Saturday morning,
but a second cyclone is progged to lift through the region on
Sunday. Longer range guidance is even less in phase with the
timing of this wave with the GFS and EC up to 24 hours off on the
timing of the surface features and the attendant precipitation.
Temperatures over the weekend look to be around normal for early


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 646 PM CDT Tue Mar 20 2018

Clearing of VFR stratus and impact on BR/FG potential is the main
challenge. Recent satellite data suggests a slower clearing is
taking place, and models are consistent with northwest winds
around 10kt not far off the surface through the night. Will keep a
BR mention at this point and keep an eye on trends for further




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