Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 182323
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
523 PM CST Sat Feb 18 2017

...AVIATION UPDATE...

.SHORT TERM...(This evening through Sunday)
Issued at 246 PM CST Sat Feb 18 2017

Weak return flow has been established across the area today as an
upper level system tracks over the southwest US. The main forecast
issue will be the potential for stratus and fog. This morning the
stratus and fog was located in northern OK, but has since mixed out
into southeastern OK. Later tonight the approaching upper level
system will allow the low level jet to increase, but focus over the
high plains. Regardless the low level winds will increase allowing
the moisture to spread northward across the entire area. There may
be the potential for fog before and after the stratus arrives.
Surface wind speeds will be relatively light and maybe some high
clouds are possible. Stratus is not forecasted to arrive until after
midnight, which could allow some time for radiational cooling. The
current dew points along and south of interstate 70 are in the lower
to mid 40s. Temperatures are expected to reach the lower to mid 40s
by sunrise, which supports the possibility of restricted visibility.
Ahead of the stratus it would most likely be more ground fog, but
once the stratus arrives the fog may dissipate or improve. At a few
locations it may mix down from the cloud base due to the advection
especially at higher elevations. The dew points are not expected to
increase much from the current state, and the boundary layer should
not fully decouple for widespread dense fog to be a big concern.
Tomorrow the models struggle with mixing out the stratus like what
is occurring is OK today. Some models are also indicating an
increase in the depth of moisture ahead of the Pacific system, which
could inhibit mixing. Although the consensus is for highs tomorrow
to reach the upper 60s to lower 70s. If clouds were to hang around
most of the day temperatures may only reach the lower 60s.

.LONG TERM...(Sunday night through Saturday)
Issued at 246 PM CST Sat Feb 18 2017

The mid/long term forecast remains largely unchanged from previous
shifts/days as model consistency in the mid-term details remains
relatively strong, and consistency in the long-term big picture is
also quite good. The main points continue to be that much warmer
than normal conditions will persist into Thursday, with an influx of
colder air likely after that time. Two storm systems will impact the
region in the coming week, the first late Sunday into Monday, and
the second late Thursday into Friday...with at least some indication
of a continued stormy pattern beyond the extent of this forecast.

Regarding the warmer-than-normal conditions, the early week storm
system has very little cold advection associated with it, and sunny
skies in its wake will keep temperatures plenty warm. Beyond that
point, upper ridging quickly takes over with neutral to warm
advection through the week. Based on recent forecast/model
verification, have gone markedly warmer with Min/Max temps from
Monday night through Wednesday, leaning heavily on the warmer side
of MOS guidance for highs and on the warmer side of operational
model guidance for lows. Thursday could be warmer as well, but will
depend more on the eventual storm track and warm sector location by
that time.

Precip chances with the first storm system Sunday night into Monday
remain fairly high especially in eastern KS, but it still appears
that not everyone will receive rain. The moisture influx into the
region is quite impressive but the mid/upper level forcing during
this period continues to appear less impressive overhead. There will
be periods of weak instability, and this along with enhanced lift in
embedded short wave troughs may bring the best chance for precip
early Monday morning although scattered showers are possible both
before and after that period. The NAM is a distinct outlier and
seems to over-moisten the boundary layer ahead of a slower upper
trough, resulting in a scenario suggestive of scattered convection
Monday afternoon...but this again is an outlier and is probably
overdone and unlikely to occur.

The second storm system late Thursday into Friday is forecast by all
operational guidance to be much more dynamically impressive locally,
but with a fair amount of uncertainty in how quickly the system will
evolve among various ensemble members. What we continue to see is a
very strong jet streak entering the central Plains by Thursday with
rapid positive feedback cycle of cyclogenesis and deepening of the
upper low. While a handful of ensemble members keep this as an open
wave, it seems equally or perhaps more likely that the system will
close off and take on a negative tilt. This will probably depend on
the speed of the trough in comparison to the translation of the jet
streak...which seems to have at least loose ties to the evolution of
a wave over the northeast Great Lakes region by mid week. As always,
it`s a complex evaluation. Current forecast focuses on the
likelihood for a strengthening system to track over KS/NE during the
period with distinct warm and cold sectors. This would suggest
potential for widespread rain and even thunderstorms within the warm
sector and widespread snow...possibly heavy and accompanied by
wind...on the cold side. Currently, snow chances increase sharply
with northwestward extent, and several model solutions suggest
snowfall in portions of north central KS...but with the qualifier
that the storm track remains quite uncertain.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday)
Issued at 523 PM CST Sat Feb 18 2017

Models continue to show low level moisture advection increasing
overnight. As a result, Some fog and stratus is forecast to impact
the terminals by the early morning hours Sunday. The forecast is
based off of the model consensus and so timing of the onset of BR
and lower CIGS may need adjustment by an hour or two once the
restricted conditions become more apparent. The RAP and NAM are
showing 925MB RH remaining high well into the afternoon implying
the stratus may be slow to scatter out. Because of this, have held
onto MVFR CIGS through the afternoon.

&&

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

$$

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



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