Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 152052
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
252 PM CST Fri Dec 15 2017

.SHORT TERM...(This evening through Saturday)
Issued at 252 PM CST Fri Dec 15 2017

Northern branch upper jet remains to the north of the central
Plains, with southern branch from southern Texas into the
southeast states with an upper low over southern Baja. High cloud
was spilling southeast ahead of a shortwave trough digging
southeast toward the Pacific Northwest, reaching the northeastern
horizon at times. Southwest winds behind the surface ridge to the
south helping push temps back into the upper 40s to lower 50s.

Temperatures are the main challenge tonight and Saturday. A stout
low level jet will develop not far off the surface with the
potential for a very strong inversion materializing as 850mb
temps warm 5-7C overnight. Mixing of this jet under clear skies
will likely bring a wide range in temps depending on local
elevation. As the upper wave to the northwest splits to the north
and southwest Saturday afternoon, a weak front pushes southeast
into the area during the day, but south to southwest winds ahead
of it and continued clear skies should allow for a noticeably
warmer day. Wend on the warm side of guidance with little cold air
advection with the front and the stronger overnight WAA to bring
highs in the mid 50s to lower 60s.

.LONG TERM...(Saturday night through Friday)
Issued at 252 PM CST Fri Dec 15 2017

Most locations should see their best chance at wetting rains in
quite some time late Saturday night into the day Sunday as the
Baja wave is eject northeast across Oklahoma and eastern Kansas
by the oncoming wave. Temperature profiles and increasing cloud by
early evening keep nearly all if not all of this precip as rain,
with far northwestern locations of the area seeing the greatest
(still small) potential for other precipitation types. This area
will be on the northwest extent of the precipitation, where there
is better potential for radiational cooling in the evening, and
temps/moisture amount aloft are not as warm/high. Have leaned
closer to the warmer GFS with the surface inversion on the NAM
seeming much too strong. South to southwest winds follow this wave
Sunday afternoon into Sunday night, keeping the lower layers
rather saturated in southern and eastern locations. Forcing for
ascent is weak at best, but will mention a small chance for light
rain into the evening.

Models do vary somewhat into the mid-week with the secondary wave
cutting off to various levels over the southwest, but upper flow
to the north does become more zonal for a warmer few days for at
least Monday and Tuesday. The 12Z ECMWF is slower and farther
north with the wave coming out around Wednesday with some chance
for rain into east central Kansas, but there is little agreement
in this scenario from the GFS ensembles.

There remains fairly good agreement with a pattern change into the
late week with upper heights building off the western Canadian
coast for a much colder regime to build into the central Plains.
An upper wave looks to rotate through the region with an
associated cold front for some chance for precipitation around
Thursday, with rain changing to snow as the cold air deepens,
though the model spread on timing of this wave, the lack of a vast
upstream snow field, and the character of the flow into Friday
for too much confidence in how fast and how cold temperatures will
get for the Thursday and Friday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1140 AM CST Fri Dec 15 2017

VFR conditions expected in a dry lower troposphere. Models
continue to trend toward low level wind shear development in a
strong inversion in the 02Z- 14Z period and will go ahead with
inclusion. FOE in particular could see stronger surface winds with
its higher elevation in this inversion for less shear.

&&

.FIRE WEATHER...
Issued at 252 PM CST Fri Dec 15 2017

Little change from previous forecast with elevated fire weather
concerns on Saturday. South winds increase in the afternoon, south
of a cold front that will slowly work through the area later in
the weekend. Strong inversion above the boundary layer keeps
extreme value of wind and humidity in check, keeping Very High
levels expected mainly south of Interstate 70 where winds are
stronger.

&&

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

$$

SHORT TERM...65
LONG TERM...65
AVIATION...65
FIRE WEATHER...65


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