Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 061112
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
512 AM CST Wed Dec 6 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 359 AM CST Wed Dec 6 2017

A few mid level shortwaves embedded within the northwest flow aloft
are forecasted to track over portions of the northern plains and
upper Midwest today. One just north of the area will move southward
this morning resulting in a weak surface trough to veer the winds.
The more substantial wave is over southern Canada and is forecasted
to drop southward during the course of today. Moisture around 850 to
700 mb is expected to move into the area ahead of this wave. By this
afternoon deep boundary layer mixing results in steep level lapse
rates coinciding with this increased moisture in the dendritic
growth layer. This deep mixing will transfer higher wind speeds down
to the surface out of the northwest with gusts up to 30 mph. Later
this afternoon and evening the models are suggesting there could be
enough lift to produce some very light precipitation as the northern
wave dives over IA and northeast KS. There are subtle hits of a band
of 850 mb frontogenesis will support this brief period of lift. This
may also be reflected in a southward moving cold front that will re
enforce the modified arctic air mass currently in place. If any
precipitation is able to form it will encounter relatively dry
surface air and temps in the lower 40s so would expect the main
precip type to be sprinkles. Temperatures dropping into the mid to
upper 30s this evening could result in flurries. These precip
chances are highest along the KS and NE stateline and far northeast
KS. By later this evening cold air advection increases behind these
waves, saturation is lost, and the lift weakens. The boundary layer
appears it will be mixed overnight allowing the transfer of strong
wind speeds to the surface. Low temperatures are expected to drop
into the teens with single digit wind chills by tomorrow morning.

.LONG TERM...(Thursday through Tuesday)
Issued at 359 AM CST Wed Dec 6 2017

By late week, the strong mid-level trough will still be stretched
across the eastern U.S., resulting in generally northwesterly flow
aloft across the central U.S.  Despite several embedded shortwaves
developing within this northwest flow, models show this mid-level
trough remaining anchored over the eastern CONUS through the weekend
and even through much of next week.  The strongest shortwave trough
developing within this mid-level pattern looks to slide across the
outlook area on Thursday, bringing another surge of cool Canadian
air into the region.  As a result, expect the coldest conditions
Thursday and Thursday night with highs only reaching near the
freezing mark and overnight lows plunging into the teens.
Temperatures late week into the weekend will rebound back toward the
seasonal normals with highs in the 40s and lows in the 20s. Slightly
warmer conditions are possible Monday as the broad mid-level trough
flattens out ahead of the next embedded shortwave trough coming out
of Canada.  As a result, more of a westerly wind component is
expected, which will aid in temperatures being a few degrees warmer
into the upper 40s/low 50s.  While precipitation from the first
embedded shortwave coming out of Canada may just skim past the CWA,
models show another wave moving in immediately behind it, with both
the GFS/ECMWF showing the potential for some light precipitation
across northeast KS Tuesday morning. While there is still plenty of
uncertainty in the amount of available moisture and the exact
tracking of this wave this far out in the forecast period, any
precipitation that fell could start as snow before transitioning to
rain with the warming daytime temperatures.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 508 AM CST Wed Dec 6 2017

VFR conditions expected through the taf period. Wind will be out
of the northwest today and increase later this morning to around
10 to 20 mph with gusts up to 30 mph. This evening the winds will
decrease, but there may enough mixing to keep it above 10 mph and
occasional gusts.

&&

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

$$

SHORT TERM...Sanders
LONG TERM...Hennecke
AVIATION...Sanders



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