Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 112315
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
615 PM CDT Wed Oct 11 2017

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Thursday)
Issued at 241 PM CDT Wed Oct 11 2017

19Z water vapor imagery shows an upper trough over the Pacific
Northwest with a flat upper ridging along the Gulf Coast. This
leaves a dry west southwest flow aloft over the central plains. At
the surface, a ridge axis was sliding east of the area as high
pressure weakened.

The forecast for tonight and Thursday is for continued dry weather
as there is little or no forcing within the flow aloft and dry air
in mid and upper levels. The main concern is for some possible
ground fog. Some of the forecast soundings show the boundary layer
saturating overnight and there should be relatively good conditions
for radiational cooling. The question is whether there is enough
moisture in the boundary layer. The RAP and NAM show surface
dewpoints holding around 50 overnight. Except for areas where the
stratus has lingered, dewpoints have mixed out into the lower and
middle 40s. So am a little hesitant to buy into the forecast
soundings boundary layer moisture. Winds will likely be light, but
there should be enough of a gradient for winds to keep from going
calm. So at this point any ground fog looks to be in the typical low
lying areas near bodies of water. Lows tonight should fall into the
mid 40s. For highs Thursday, have trended them warmer. Models prog
pretty good low level warm air advection with 925MB temps warming to
around 21C across central KS. With good insolation, think highs will
be in the middle 70s to near 80.

.LONG TERM...(Thursday night through Wednesday)
Issued at 241 PM CDT Wed Oct 11 2017

Initial upper wave pushing east across the northern Plains settles a
cold front into the area late Thursday night, with all guidance
agreeing it will hang up across the area for the next few periods
as it becomes parallel to the mid- and upper-level flow. Initially,
the mid and upper layers are rather dry, but will need to watch
depths of the cloud layer and persistent low-level frontogenesis for
drizzle and perhaps a few showers behind the front in the
north and west Friday and Friday evening before moisture depths
rapidly increase, with PW values in the 1.5-2 inch range Friday
night into Saturday evening. Elevated showers and thunderstorms
will likely increase Friday night into early Saturday and play a
large role in severe weather potential for Saturday afternoon and
evening. Areas that stay in relatively clear air will likely see
ML CAPE values around 1200 J/kg and strong low- and deep-layer
shear, though mid-level lapse rates and low-level CAPE are not
impressive. Secondary front surges through Saturday night with the
remainder of the weekend looking dry. With the very high PW air
for this time of year and low-level baroclinic zone nearly
stationary for a period or two, there are ingredients in place for
heavy rainfall as well, though not too dissimilar to last
weekend, overall forcing for persistent ascent is not apparent.
The front`s location across the area also creates wide spreads in
high temperature potential for Friday and Saturday. Expect a much
tighter gradient than currently forecasted, with locations in the
north and west more likely to be cooler as opposed to warmer than
depicted.

Modified surface anticyclone settles in Sunday night and presents a
good environment for radiational cooling, though nature of this
airmass suggests anything more significant than a frost would be
unlikely. After a cooler Sunday, temperatures should modify into the
midweek as weaker zonal to northwest flow pattern builds overhead.
Differences increase in the pattern around Wednesday with models
struggling in how to handle energy in the fast jetstream over the
northern Pacific Ocean, but rich moisture availability is very
hard to come by locally and keeps the Monday to Wednesday periods
dry.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 612 PM CDT Wed Oct 11 2017

Have kept a VFR forecast going for the period. Some models
continue to pick up on radiational fog development tonight,
especially at TOP/FOE by early morning. For now, expect if
anything is to form it would be shallow and in low lying areas.
Southerly winds begin to pick up tomorrow after 18Z with gusts up
to 23 knots seen near MHK.

&&

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

$$

SHORT TERM...Wolters
LONG TERM...65
AVIATION...Heller



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