Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 170859

Area Forecast Discussion
National Weather Service Topeka KS
259 AM CST Sun Dec 17 2017

.SHORT TERM...(Today and tonight)
Issued at 258 AM CST Sun Dec 17 2017

Early this morning an upper level trough was lifting northeast
across north central OK and south central KS. The PV anomaly max
extended from northwest of ICT, southeast to TUL. Ahead of the PV
anomaly there was stronger ascent moving northeast across the
southern counties into east central KS. A band of light rain has
developed and at 2 AM extended from north of TOP, southwest to east
of SLN. This band of rain will move northeast across the eastern half
of the CWA through the morning hours. As the upper trough lifts
northeast across eastern KS, the stronger ascent will shift
northeast of the CWA by 18Z and we should see our rain chances come
to an end. East central KS may see 0.10 to 0.20" of rainfall this
morning with much lesser amounts across the western counties. If
light rain or sprinkles make northward into north central KS then
there is a chance that some of the rain may mix with a bit of snow
along the NE border from 12Z through 15Z.

A weak cold front will move southward across the central counties of
the CWA but frontolysis will occur and the front should become less
defined during the late afternoon hours into Tonight. Expect the
eastern half of the CWA to remain mostly cloudy Today with slowly
decreasing cloud cover across the western counties during the late
afternoon hours. Highs will only reach the lower 50s across east
central KS with mid 40s across north central KS.

Tonight, A few of the numerical models show some weak isentropic
lift developing across eastern KS this evening. This may result in
patchy drizzle or some very light rainfall. Temperatures will be
above freezing if any drizzle were to occur. Since the QPF will be
only a trace I kept any POPs out of the forecast. Late Tonight
temperatures will drop off into the lower to mid 30s across east
central KS with mid 20s across north central KS as skies clear from
west to east.

.LONG TERM...(Monday through Saturday)
Issued at 258 AM CST Sun Dec 17 2017

Any chance for significant sensible weather changes in the long
term forecast will have to wait until the Thursday day and evening
time frame.  In the meantime, upper confluent type flow regime sets
up over the central Plains region.  This along with broad low
amplitude mid level ridging will allow for warmer than normal temps
to be the story.  Highs Monday through Wednesday should be quite
pleasant generally in the 50s and possibly low 60s over northeast
Kansas.  Meanwhile lows only dip into the 30s at most locations with
the lowest lying areas seeing upper 20s.

Thursday into Friday will see the pattern change and hinges on the
evolution of an Aleutian Low pressure system as it slams into the
Pacific Northwest region of the CONUS.  At this time, 17.00Z
EC/GFS/Canadian solutions seem to be coming into better agreement
that the upper pattern will essentially split once again as the
previously mentioned low advances into the Northern Rockies.  Some
energy remains with a portion of the northern PFJ and a portion
dives south into the Desert Southwest.  Eventual solutions show a
deep positively tilted trough extending from central Canada into the
southern Plains with the trough broadening into the Christmas Eve
time frame with reinforcing shots of cold dry Arctic air moving into
the northern and central Plains.  Precip chances for Thursday are
still much in question with a low level frontogenetical response
moving through the area (best upper forcing remains northeast and
south of the forecast area).  But, the consistent theme is to keep
best rain/snow chances generally north of I-70.  Amounts still very
hard to know, but the hint is only light amounts may be the eventual
result.  Again, cold enough air being entrenched in the region for
all snow is unlikely at this point.  Temps might be the biggest
story in the end with this frontal system.  There remains a large
spread in outcomes at this point amongst the models in exactly how
much cold air gets pulled in Thursday night with strong CAA and then
subsequent periods.  The higher confidence outcome will result in
below normal temps though with highs struggling to reach into the
mid 30s and low temps plummeting into the low teens and possible
single digits by Christmas Eve.  So, while it may not be a white
Christmas, it will likely be a cold one.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1128 PM CST Sat Dec 16 2017

VFR expected through 09Z then a transition to MVFR cigs thereafter
as shra moves into or develops over the terminals. Models suggest
precipitation should end in the 15Z-18Z period with mvfr to vfr
cigs expected through the end of the period.




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