Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 201119

Area Forecast Discussion
National Weather Service Topeka KS
619 AM CDT Tue Mar 20 2018

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 403 AM CDT Tue Mar 20 2018

There is a midlevel shortwave trough currently located over central
NE and it is tracking southeastward towards northeast KS. Slight
upper-level potential vorticity advection and midlevel differential
vorticity advection seems to be the forcing responsible for light
rain showers across the forecast area this morning. Given the
strength of this shortwave the temperature advection has been rather
minimal, but the low-level pressure gradient in place is forcing
temperatures in the mid 30s southward into portions of northern KS.
The current cloud cover and partially mixed boundary layer is
inhibiting temperatures from dropping any lower. Given the shallow
low-level melting layer some snow has mixed in with the rain showers
in far northern KS. The amount of QPF expected this morning is minor
so impacts from any snow should be minimal. The rain becomes focused
across far eastern KS late this morning as the shortwave continues
progressing southeastward.

Most of the precipitation should end around mid day. The HRRR is
showing steepening low-level lapse rates with some residual moisture
still present, which could result in some instability showers during
peak diurnal heating later today. The RAP and HRRR are also trending
to keep the stratus around much longer than previously thought.
Current satellite shows stratus stretching back towards Rapid City
and winds continue out of the northwest all day. So unless daytime
mixing or dry advection can erode some of this stratus it could
continue through this evening. Portions of central KS have the
highest chances of scattering out while far northeast KS looks to
remain entrenched. As a result highs today have been lowered into
the mid to upper 40s, but may need to be dropped a few more degrees.
Surface wind gradually diminish through out the day as a surface
ridge moves into the area this evening. As the clouds scatter out
this evening winds go light to calm, which could set the stage for
radiation fog tonight. Although winds just above the surface are not
forecasted to decrease as much so this could disrupt the boundary
layer decoupling. Lows tonight should drop to around 30 degrees for
most locations.

.LONG TERM...(Wednesday through Monday)
Issued at 403 AM CDT Tue Mar 20 2018

By Wednesday, models finally show the northwesterly flow aloft from
the mid-level trough over the eastern U.S. shifting further east of
the CWA as a mid-level ridge begins to build into the central U.S.
With surface high pressure gradually shifting east of the area
through the day on Wednesday, the combination of dry conditions with
mostly sunny skies and light southerly winds will support afternoon
high temperatures warming into the 60s.

A large closed mid-level low looks to slide into the Pacific
Northwest by Thursday, with a broad mid-level trough developing
across much of the western U.S. by Friday and continuing to deepen
through the weekend.  As this trough deepens over the western U.S.,
it will help to push an area of surface low pressure eastward into
Kansas, resulting in a decent pressure gradient setting up with
breezy southerly winds, so have increased winds a bit Thursday into
Friday. This southerly flow will support continued WAA through the
end of the week with high temperatures Thursday and Friday soaring
into the 70s.  Models show the surface low progressing eastward
across Kansas Friday and Friday night, with a warm front progged to
gradually lift northward over the CWA before the associated cold
front tracks to the east on Saturday.  While models continue to come
into better agreement with the timing and tracking of this surface
low Friday into Saturday, the GFS continues to be the most robust
with precipitation development over the CWA. In contrast, the
ECMWF/Canadian remain predominantly dry across the CWA with any
precipitation chances remaining focused near the KS/NE border.  As a
result, confidence remains low with the location and coverage of any
precipitation development Friday into Saturday. However, if
precipitation is able to develop, conditions would be conducive for
some elevated thunderstorm development. As this system continues to
progress eastward over the area on Saturday, there is the potential
for a north-south temperature gradient to develop due to wrap-around
precipitation potentially near the KS/NE border with drier
conditions into central KS. Despite winds shifting to the northwest,
the advection of cooler air will lag well behind this system. As a
result, Saturday highs still look to range from the low 60s to mid
70s with Sunday highs dropping into the 50s/60s.  Models show
another embedded shortwave within this advancing broad trough moving
into the central U.S. late weekend into early next week, however
there are significant model discrepancies with the timing/tracking
of any precipitation associated within this next wave.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 609 AM CDT Tue Mar 20 2018

MVFR/IFR ceilings have been slow to move over the taf sites. The
trend may be to keep MVFR going until this afternoon then it
scatters out this evening. There is a slight chance for ground fog
late tonight as the skies clear and winds go calm.




SHORT TERM...Sanders
LONG TERM...Hennecke
AVIATION...Sanders is the U.S. government's official web portal to all federal, state and local government web resources and services.