Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 110534
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
1134 PM CST Sat Dec 10 2016

...AVIATION UPDATE...

.SHORT TERM...(This evening through Sunday)
Issued at 321 PM CST Sat Dec 10 2016

On Saturday afternoon, fast zonal flow was dominating the mid and
upper level flow pattern with embedded vorticity maxima crossing
mainly the northern Plains with weaker impulses farther south. A lee
surface low was strengthening today with increasing low level
southerly flow across the Plains states. Moisture was beginning to
increase from north Texas into Oklahoma, and this deeper low-level
moisture will continue to stream toward eastern Kansas tonight.
Persistent isentropic upslope flow and moisture advection into the
area will result in a deepening stratus deck, and should eventually
see some drizzle squeezed out of these low clouds...most likely
between 3 AM and Noon. While temperatures may drop below freezing
this evening, warm advection overnight should result in increasing
temperatures after midnight and any drizzle would very likely
coincide with temperatures above freezing. Clouds will persist much
of the day on Sunday, especially in eastern KS, limiting
temperatures in the 40s despite the continued warm advection. By
afternoon, a cold front will begin to cross the forecast area with
cold advection keeping highs in north central KS in the upper 30s.

.LONG TERM...(Sunday night through Saturday)
Issued at 321 PM CST Sat Dec 10 2016

Quasi-zonal to northwest flow aloft continues through early next
week. A strong shortwave will track over southern Canada, which will
push a cold front through the region Monday night into Tuesday. The
cold front is expected to be dry, but the air mass will be much
colder. Highs on Monday will generally be in the 40s while on
Tuesday they stay in the lower to upper 20s. Surface high pressure
will dominate the northern half of the US into mid week. Towards the
end of the week the shortwave activity over the Pacific northwest
will increase. As one of the waves moves over the central Rockies
the flow aloft becomes more southwesterly. Warm air advection
pattern will set up across the plains as the high pressure retreats
eastward. As the mid level moisture advects eastward into the region
isentropic lift will increase over the cold dome. In response to the
waa snow may develop mainly across far northern KS, but only a small
amount of QPF is possible. Also, the snow will have to fight a deep
dry air mass near the surface. Into Friday low level moisture
finally reaches eastern KS with temperatures below freezing. There
will be no ice present in the cloud so depending on the strength of
the lift freezing drizzle may be possible. The wave over the Rockies
could force a warm front northward causing temperatures to rise
above freezing at some point. Unfortunately the models begin to
diverge on where these surface features may end up not to mention
how to handle the wave train over the western US. There does appear
to be another reinforcing shot of cold air. Whether there is precip
during this time frame is uncertain as well as the precip type,
which could even go through several transitions. Models do agree
that the QPF amounts are not that high at this point.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1134 PM CST Sat Dec 10 2016

Low level moisture is beginning to move north through central OK.
Forecast soundings from the RAP and NAM have consistently shown
stratus advecting back into the terminals before daybreak. Biggest
uncertainty is how low the stratus will be. Most OBS upstream have
the CIGS around 2 KFT but forecast soundings suggest IFR and
possibly LIFR CIGS. Not sure I have that much confidence in LIFR
thinking decent mixing of the boundary layer may prevent CIGS from
getting to low. In any case, have included a tempo for IFR CIGS
and -DZ. Will be monitoring the stratus as it moves north.

&&

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

$$

SHORT TERM...Barjenbruch
LONG TERM...Sanders
AVIATION...Wolters



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