Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 191738
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1138 AM CST Fri Jan 19 2018

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 357 AM CST Fri Jan 19 2018

The midlevel trough that will impact our weather this weekend is
currently located just off the west coast of CA and is forecasted to
cut off from the main flow as it deepens over the Four Corners
region. Ahead of the approaching trough westerly flow aloft is
supporting the lee-side trough, which has resulted in an increase in
the lower tropospheric pressure gradient. A low level jet centered
around 925 mb with an axis bisecting the forecast from west to east
has kept the boundary layer from fully decoupling. This nocturnal
mixing has moderated the temperatures this morning therefore lows
have been adjusting accordingly. Today highs will vary based on the
relatively deeper snow cover which still exists across portions of
central KS and extending into far southeast NE. These areas will
remain in the 40s while remaining locations are able to reach the
50s given the return flow in place.

.LONG TERM...(Saturday through Thursday)
Issued at 357 AM CST Fri Jan 19 2018

By Saturday morning surface high pressure over the southeastern US
should progress far enough eastward to allow gulf moisture to spread
northward towards the area. There is some model agreement regarding
the moisture timing and quality although models can tend to be
too fast with the arrival. As of now this anomalously high
moisture could arrive in the form of stratus and or fog sometime
early Saturday. Although given the wind speeds decided not to
include fog in the forecast. Lee-side cyclogenesis occurs in
southeast CO as the deepening midlevel low pressure ejects out of
the Rockies. An inverted surface trough develops across eastern
KS, which will set up a modest baroclinic zone in the forecast
area by Sunday morning. With the boundary layer moisture in place
any lift could result in drizzle or freezing drizzle in the
morning, but by the afternoon temperatures warm above freezing.
Surface low pressure begins to lift northeast as the midlevel
tracks over KS and NE. Models are showing a modest EML that could
prevent any precipitation despite that large scale lift. The
potential for fog may increase Saturday night as winds within the
inverted trough axis become light. Also, model soundings indicate
stratus could be somewhat discontinuous and therefore radiational
cooling becomes a possibility as well.

Towards Sunday afternoon the EML dissipates in response to the
midlevel low pressure, which introduces the chance for rain
showers and possibly thunder. Steep midlevel lapse rates could
exist just ahead of the synoptic dry punch and become co-located
over the mid 50 dew points over far eastern KS resulting in MUCAPE
upwards of 200 j/kg. The most likely scenario is that if showers
and storms initiate along the synoptic cold front/dry line in far
eastern KS they will quickly race northeastward. There is a low
probability for these storms to become strong with sufficient deep
layer shear in place. On Sunday evening the southern edge of a
developing deformation zone tracks over north central KS on the
backside of the low pressure. Temperatures should already be close
to freezing on the poleward side of the inverted trough so snow
should be the dominate precipitation type once the lift increases.
How far this deformation zone wraps around the system will dictate
the eastward extent of the snowfall. As of now accumulations
appear to be minor and confined to north central and far northeast
KS. Temperatures moderate back to near normal values next week
with highs in the 40s and lows in the 20s. Another midlevel system
looks to possibly track over the western US and central Rockies
towards the end of the week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1137 AM CST Fri Jan 19 2018

VFR conditions are expected through early morning. Reduced
ceilings will move in from the south near 12-14Z as a stratus deck
moves into the area. While some soundings indicate accompanied
lower visibilities, believe that with the gusty winds continuing
through the evening, stratus will prevail. Kept ceilings at MVFR
for now, but IFR may be seen by the very end of the period.

&&

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

$$

SHORT TERM...Sanders
LONG TERM...Sanders
AVIATION...Heller



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