Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 161121
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
521 AM CST Tue Jan 16 2018

...AVIATION UPDATE...

.SHORT TERM...(Today and tonight)
Issued at 227 AM CST Tue Jan 16 2018

08Z water vapor imagery shows a closed upper low over the Great
Lakes with a trough axis rotating through the central plains.
Another closed low was noted over the Gulf of Alaska with a high
amplitude ridge between the two upper lows. At the surface, an
arctic high was centered over the Dakotas and cold dry air continued
to advect south.

For today and tonight, the cold dry airmass should preclude any
chance for measurable precip. Especially considering upper level
subsidence will be on the increase through the day as the upper
trough axis passes to the south of the forecast area. However there
have been a few isolated snow showers this morning with some reports
of a light dusting. Forecast soundings maintain dry adiabatic lapse
rates in the boundary layer with some saturation around 3 KFT. The
question is whether the saturation will be deep enough to squeeze
out some flurries. Will opt to not include a mention of flurries
since dry air advection should persist. Nevertheless the day shift
will want to monitor trends. Another concern will be how solid a
stratocu deck becomes. Since low level cold air advection will
likely persist through at least the morning, if insolation is
limited highs may not reach the teens. Model progs of low level RH
suggests scattered or perhaps broken clouds so am choosing to be
optimistic there will be some sunshine today. For now models suggest
the eastern counties may see more cloud cover. So have highs around
10 in the east and a couple degrees warmer over north central KS
where sunshine is more likely. Tonight the center of the surface
high should pass over the area. Clear skies and light winds should
help lows fall to around zero. For now think there is a reasonable
chance winds go calm with the boundary layer decoupling. However the
pressure gradient could strengthen before sunrise over central KS as
the surface high propagates south. If there is some wind, wind chill
values could approach 15 below.

.LONG TERM...(Wednesday through Monday)
Issued at 227 AM CST Tue Jan 16 2018

By Wednesday, mid-level troughing will shift into the eastern U.S.,
with northwesterly flow in place across the central U.S. through
Thursday. With surface high pressure sliding into the southeastern
U.S. Wednesday and remaining there into this weekend, the shift to
south/southwesterly surface winds will aid in temperatures
moderating through the latter half of the week.  As a result, expect
highs in the mid 20s to low 30s on Wednesday with temperatures
rising into the low 50s by Friday, which is at least 10F degrees
above the seasonal normals.

Models show a mid-level trough beginning to advance into the
northwestern U.S. on Friday, with this trough deepening as it tracks
over the Rockies Saturday/Saturday night.  This advancing trough
will help to push surface low pressure into western KS by Friday
night, with an associated front tracking into the CWA by Saturday
morning and likely stalling out over the area. However, there are
still some discrepancies with the exact location of this front over
the CWA, which will have an impact on temperatures as there may be a
high-temperature spread of roughly 10F degrees on Saturday.  As the
mid-level trough progresses east of the Rockies early Sunday morning
with a closed-low potentially developing over KS, models show the
surface low over the TX/OK panhandles shifting northeastward into
eastern KS. This tracking of the low would suggest the stalled
southwest-to-northeast oriented front would become more south-to-
north oriented over eastern KS before finally advancing east of the
area through the afternoon.  Some scattered light precipitation may
be possible Sunday morning, with the potential for the dry slot to
develop over portions of the CWA. However, some wrap-around
precipitation on the back side of the surface low may skim across
far north central to far northeast KS Sunday night before exiting
the region Monday morning. With this system still several days out,
it is difficult to fine-tune the timing, location, and precipitation-
type details.  However, at this time, model guidance suggests we may
have some dry-air aloft that will need to be overcome before enough
saturation is present in the dendritic growth zone to support
precipitation transitioning to snow.  Also, the location of the
pivoting front will impact the temperature spread across the
forecast area and, thus, the expected precipitation type.

This mid-level trough will quickly lift into the Great Lakes region
on Monday, with mid-level flow over the central U.S. becoming more
zonal.  At this time, do not expect much cold-air advection behind
this front due to this mid-level flow and westerly surface winds in
place on Monday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 521 AM CST Tue Jan 16 2018

Watching satellite trends has allowed confidence in MVFR CIGS
moving in to increase. And the RAP and to a degree the GFS support
the low clouds continuing to move south. With forecast soundings
maintaining dry adiabatic lapse rates in the boundary layer, there
could be some flurries. However OBS immediately upstream are not
showing much until you look back into central and northern IA. So
will not include a mention of flurries just yet and monitor
trends. The stratocu deck is expected to diminish towards the late
afternoon as the cold air advection diminishes and large scale
subsidence increases. This should lead to VFR conditions through
the night.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Wind Chill Advisory until noon CST today for KSZ008>012-020>024-
026-034>040-054>056-058-059.

&&

$$

SHORT TERM...Wolters
LONG TERM...Hennecke
AVIATION...Wolters



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