FXUS63 KTOP 162120

Area Forecast Discussion
National Weather Service Topeka KS
320 PM CST Sun Dec 16 2018

.SHORT TERM...(This evening through Monday)
Issued at 320 PM CST Sun Dec 16 2018

Aside from the chance of fog in valleys tonight, expect continued
quiet and seasonably warm conditions.

Early afternoon water vapor imagery depicted a shortwave trough
diving southeastward through the Central Plains along the
downstream flank of a longwave ridge situated over the Rockies.
High clouds had pushed well east of the area, leaving clear skies
over northeast Kansas. Little in the way of upstream cirrus was
noted until western South Dakota, but these clouds should stay
mostly north and east of the forecast area tonight with the H500
ridge axis building eastward into central Kansas.

A 1028 mb surface high pressure cell centered over western
Nebraska slides eastward tonight in tandem with the upper
tropospheric ridge and will be centered over the forecast area
tonight. Lower tropospheric moisture has actually been on the rise
today ahead of the ridge with dewpoints 10-15 degrees higher than
this time yesterday at many locations along and north of I-70.
This moisture, coupled with the light winds under the ridge axis,
should allow for the formation of fog tonight in favored river
valley locations. For now have kept patchy wording in the
forecast, but there is a modest chance that fog could be more
widespread if temperatures cool off faster than forecast.

Surface high pressure lingers well into Monday, with return flow
starting to increase in central and western Kansas by the
afternoon hours. With little in the way of CAA associated with
this surface high, H850 temps will only change a few degrees over
the course of the period, with WAA commencing Monday afternoon.
High clouds may start to increase Monday afternoon with a region
of DCVA ahead of a weak negatively-tilted wave working through
Southern Plains along the subtropical jet.

.LONG TERM...(Monday night through Sunday)
Issued at 320 PM CST Sun Dec 16 2018

Other than a slight chance of rain in east-central Kansas on
Wednesday, little sensible weather is forecast for the rest of the
week into next weekend.

Multiple PV lobes embedded within a broader longwave trough
affect the area from Tuesday into Wednesday, with the primary
longwave amplifying on Wednesday, ushering a frontal boundary
eastward across the forecast area. The timing of the return
moisture will be key to the areal extent of precipitation in east-
central Kansas on Wednesday as the boundary moves through. Enough
kinematic forcing may phase with the weak baroclinicity along the
lower-tropospheric boundary to fuel scattered rain showers, but
overall the threat for organized rainfall appears quite low.

The pressure gradient tightens over the central CONUS on Thursday
as the aforementioned upper level trough digs into the Southern
Plains and cyclogenesis takes place over the Ark-La-Miss region.
The push of CAA accompanying this pattern shift only lingers into
Friday morning before upper level longwave ridging amplifies for
Friday into Saturday. Model solutions diverge quickly on how the
pattern evolves beyond Saturday as the ridge breaks down. Aside
from the 24 hours from midday Thu to midday Fri, the overall
airmass undergoes little change and temperatures should remain at
or above normal for this time of year.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1120 AM CST Sun Dec 16 2018

VFR conditions are expected for today with the possibility of
patchy fog in low-lying areas tonight, clearing out after
sunrise. Winds will predominately be out of the north, becoming
variable overnight.




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