Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 111714

Area Forecast Discussion
National Weather Service Topeka KS
1214 PM CDT Wed Oct 11 2017


.SHORT TERM...(Today and tonight)
Issued at 253 AM CDT Wed Oct 11 2017

Surface high pressure currently stretches across central KS in the
wake of the mid level low pressure system. Dry air has worked into
the area with dew points ranging from the lower 30s to lower 40s
with the lowest values within the ridge axis. Clear skies and calm
winds have allowed temperatures to dip into the mid 30s. Across
portions of eastern KS low level moisture in the form of stratus
remains in place. Current satellite imagery depicts very slow
eastward progression of the western edge of this stratus deck. The
consensus of model guidance is to clear the forecast area by late
this morning. Temperatures will likely stay in the mid 40s under
this cloud deck so there will be a very sharp temperature gradient
somewhere near highway 75 in the predawn hours. The vertical wind
profile is still showing 925 mb wind speeds around 25 kt, which
could be enough for partial mixing. Down in the valleys it appears
the boundary layer has fully decoupled so temperatures may be
slightly cooler and efficient for frost.

Modification of the post frontal air mass will take place today with
the aid of sunny skies and light southerly winds. Highs should reach
the lower to mid 60s. Boundary layer moisture will advect back into
the area today as the high pressure center gradually retreats into
MO. By this evening and into tonight portions of eastern KS will be
situated along the western periphery of the high which is usually a
favorable location for the development of fog and it appears that
the model guidance agrees with at least patchy fog. Further into
central KS a weak pressure gradient is expected to set up. This
along with the lack of appreciable moisture return will likely
inhibit fog. Lows tonight will only drop into the lower to mid

.LONG TERM...(Thursday through Tuesday)
Issued at 253 AM CDT Wed Oct 11 2017

Thursday through Friday, An upper level trough across the
Pacific northwest will amplify as it digs southeast across
the western conus. A downstream upper level ridge will amplify
across the the eastern conus. Increasing southwesterly mid
and upper flow across the plains will cause a lee surface trough
to deepen across the central and southern high plains. The
resulting pressure gradient will cause southerly winds to increase
across eastern KS. The resulting WAA will help high temperatures
to warm int the mid to upper 70s on Thursday, with highs in the
mid to upper 80s across much of the area on Friday. A surface cold
front will push southward across western KS as the lee cyclone
deepens across southeast CO and northeast NM during the day on
Friday. The front may move southeastward into the northwest
counties of the CWA during the afternoon hours on Friday. At this
time a stronger EML will advect across the warm sector, thus there
should be a strong enough cap to prevent surface based convection
along the surface front Friday afternoon.

Friday night through Saturday night, The 00Z NAM model shows
a stronger push of shallow cold air southward across central
high plains. If the NAM solution were to verify the front may
push southward into northern OK late Friday night. But as the
H5 trough approaches stronger ascent will overspread the central
plains and combined with isentropic lift north of the front will
cause showers and elevated thunderstorms to develop late tonight
and through the early morning hours. The 00Z GFS and 00Z ECMWF do
not show as strong of a southward push on the boundary and has it
stalling out early Saturday morning across central and southern
KS. The GFS and ECMWF show the front lifting back northward as
warm front into southern NE by Saturday afternoon. If both of
these model solutions were to verify then the stronger isentropic
lift will shift northeast of the CWA during the mid and late
morning hours of Saturday and we could see a break in the showers
and thunderstorms into the early afternoon hours. As the H5 trough
across the central Rockies shift east into the plains late
Saturday afternoon and into the night, a surface front will push
southeast across the state of KS. The surface front will move into
central KS during the afternoon hours where surface convergence
ahead of the front combined with the larger scale ascent ahead of
the approaching H5 trough will cause showers and thunderstorms to
develop. Deeper gulf moisture will already be in place across the
plains and mid-level lapse rates should be steep enough for MLCAPE
to be in the 1500-2500 J/KG range. Given a southwesterly jet max
at H5 of 50 to 60 KTS, 850mb winds from the south-southwest at 40
KTS and southerly surface winds there will be enough vertical
windshear combined with adequate CI for severe thunderstorms,
possibly supercell thunderstorms if they initially remain discrete
but linear forcing will increase along the front through the late
afternoon hours and will cause the discrete storms to congeal
into a line of thunderstorms. This line of storms could be severe
with damaging winds and any embedded supercell structures in the
line could produce large hail. The line of strong to possibly
severe thunderstorms will push southeast across the CWA during the
evening hours. Post frontal showers and thunderstorms will
continue through Saturday night as the H5 trough moves east across
the plains. Highs on Saturday afternoon will be dependent on how
far the warm front shifts northward during the morning hours. At
this time both the ECMWF and GFS show the front lifting north of
the NE border by 18Z SAT. If we get some insolation during the
afternoon hours, highs could reach the lower to mid 80s. At this
time I`ll keep the 80 degree readings across east central KS with
70s across the remainder of the CWA.

Sunday, The post frontal showers will linger into the morning
hours but after 18Z SUN the H5 trough will shear out as it moves
east into MO and northeast OK, so the rainshowers should shift
east of the CWA by noon on Sunday. Skies should clear from west
to east across the CWA Sunday afternoon. Highs will cool back i
into the lower to mid 60s.

Monday through Wednesday, The upper flow will become zonal with
the stronger mid level jet max remaining across the northern US
and Canada. Highs will gradually warm into the lower 70s on Monday
with mid 70s Tuesday and Wednesday.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1214 PM CDT Wed Oct 11 2017

RAP and NAM forecast soundings continue to show radiational fog
developing overnight. However their progs show dewpoints being
around 50 when there is still quite a bit of dry air over the
region and nothing very close to advect in. Additionally there
should be some wind overnight. Am not confident in the forecast
soundings and think if there is some fog it may be more along the
lines of shallow ground fog in the river valleys. So will not
include a mention for now and monitor boundary layer moisture
through the afternoon for hints on likelihood of radiational fog.
Otherwise VFR conditions should prevail.




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