Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 092323
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
523 PM CST Sun Dec 9 2018

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Monday)
Issued at 300 PM CST Sun Dec 9 2018

19Z water vapor imagery shows an upper closed low spinning over
Nebraska. A ridge was located over the Great Basin ahead of a deep
trough moving toward the Pacific Northwest coast. The closed low
over Nebraska will drop southward tonight moving directly over the
area, but will have very minimal impacts on conditions. Surface
winds will remain light tonight under mainly clear skies. Patchy
fog, especially near river basins, is possible again tonight.
Temperatures will drop into the teens so areas that experience fog
could see a minor glazing of ice deposit on ground.

Surface high pressure will dominate conditions in the area tomorrow.
The high will slide southeast with time and surface winds will shift
to more of a southerly direction by late in the day. After a cold
start, temperatures are expected to warm to near normal in the low
40s under mostly sunny skies.

.LONG TERM...(Monday night through Sunday)
Issued at 300 PM CST Sun Dec 9 2018

Progressive disturbances embedded in fast mid/high-level flow
branches of a multi-stream pattern aloft will prevail into next
weekend. Related short-duration return-flow episodes will serve to
negate any prospects for appreciable moisture return in advance of
multiple surface boundaries crossing the region in association with
the progressive pattern aloft.

On Tuesday, surface lee troughing over the central High Plains will
be enhanced by modest differential cyclonic vorticity advection
preceding poorly phased midlevel vorticity maxima extending from the
northern Plains to the Desert Southwest. The accompanying tightened
surface pressure gradient peripheral to this surface feature will
support gusty south-southwest winds across the region Tuesday
afternoon, supporting warm-air advection. Ample dry air through the
lower troposphere coupled with enhanced-wind-induced boundary-layer
turbulence will correspond to deepened vertical mixing, with high
temperatures on Tuesday expected to reach into the upper 40s to
lower 50s. Readings into the middle 50s cannot be ruled out Tuesday
afternoon in east-central KS in proximity to a low-level, downslope-
flow-enhanced, warm-thermal ridge emanating from the High Plains.
Should warmer temperatures be realized, in association with deeper
mixing and a drier boundary layer, some potential for surface RH to
fall into the 30s in combination with the breezy winds could exist.
As a result, locally elevated fire-weather conditions cannot be
ruled out given adequately dry fuels in east-central Kansas on
Tuesday -- and this potential will be highly conditional upon the
evolution of the low-level thermal profile. If high clouds were to
spread across the area ahead of the trough reducing diurnal surface
heating/mixing, and given the lack of an even warmer antecedent air
mass, the fire-weather potential would be considerably mitigated.

A component of the lee trough will develop northeastward across KS
through Tuesday evening/night, with a southwestward-trailing cold
front tracking across the region. The passage of this boundary will
be accompanied by winds shifting to the west/northwest along with
the initiation of modest cold-air advection. Compared to Tuesday,
slightly cooler temperatures are expected on Wednesday with highs
expected to reach the lower/middle 40s.

For late this week, medium-range model guidance continues to suggest
amplification, and perhaps some phasing, of the mid/upper-level
pattern, with a strongly-deepening cyclonic perturbation embedded
within the southern component of the aforementioned multi-stream
pattern. The latest multi-model consensus is suggesting that the
most likely trajectory of the evolving strong cyclone will be
generally eastward from the southern Plains toward the southern
Atlantic Coast. This will keep the forecast area on the cool side of
the baroclinic zone along which the cyclone tracks, with little
opportunity for significant precipitation chances owing to the lack
of any influx of appreciable theta-e accompanying the cyclone-
attendant warm conveyor belt. Nevertheless, sufficient ascent will
exist across north-central KS for Thursday morning ahead of the
midlevel trough for a chance of light snow/rain, while the
developing deformation zone of the maturing cyclone could glance
parts of east-central KS Thursday afternoon. The latter scenario
should mainly be accompanied by light rain, though pockets of
light snow could mix with the precipitation owing to lower-
tropospheric cold advection northwest of the surface low center --
yielding descending wet-bulb-zero heights. Precipitation amounts
for Thursday are presently forecast to be too minimal for
substantial impacts.

Growing dispersion among model solutions into Friday and Saturday
casts increasing uncertainty regarding the upper-air pattern over
the CONUS. Nevertheless, precipitation chances are presently minimal
for Friday and Saturday owing to the combination of limited
predictability regarding any salient boundaries and their probable
lack of phasing with adequate moisture. Temperatures are presently
forecast to be near normal for Friday into Saturday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 519 PM CST Sun Dec 9 2018

For the 00z TAFs, VFR conditions are expected through the period.
There is the potential for some very patchy fog to develop
overnight into Monday morning, however confidence in any MVFR
visibilities remains low.

&&

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

$$

SHORT TERM...Teefey/Cohen
LONG TERM...Cohen/Teefey
AVIATION...Hennecke


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