Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 140437
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1137 PM CDT Wed Sep 13 2017

...AVIATION UPDATE...

.UPDATE...
Issued at 1045 PM CDT Wed Sep 13 2017

Have updated the forecast to spread 20 to 30 percent POPs further
east for the overnight hours and into Thursday morning. Models
continue to show a mid level warm air advection pattern and now
more solutions are developing isolated to scattered showers
generally between 09Z and 15Z. forecast soundings suggest there
could be as much as 500 J/kg of elevated CAPE. So there may be
some late night rumbles of thunder.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 314 PM CDT Wed Sep 13 2017

This afternoon a mid-level ridge stretched from the southwestern
U.S. into the central U.S., with water vapor imagery showing
increasing cloud cover over the Pacific Northwest from an advancing
mid-level trough.  Models show this trough deepening across the
western U.S. through Thursday, which will help to push surface low
pressure currently near the CO/KS border further east into Kansas.
This advancing low pressure will cause an increasing pressure
gradient overnight and through the day on Thursday, with short-range
guidance showing winds beginning to increase by sunrise. Models
continue to show the potential for some weak embedded shortwaves to
develop within the flattening ridge axis in southern NE.  While
there looks to be modest isentropic lift present overnight into
Thursday morning (primarily across north central KS), expect
cloud bases around 10,000ft with very dry air beneath it.  Most
models show a very shallow mid-level saturation layer, with the GFS
being an outlier in showing a deeper saturated layer.  All-in-
all, while a stray shower/isolated cannot entirely be ruled out,
confidence is low in precipitation being able to develop and reach
the ground through the deep dry layer.  For overnight into Thursday
morning, have kept low-end slight chance PoPs across far north
central KS where the better isentropic lift is focused.  With
increasing mid-level cloud cover expected from these weak embedded
shortwaves and with steady/slightly-increasing southerly winds
likely overnight, short-range guidance shows temperatures over north
central KS becoming nearly steady near sunrise, which should keep
lows a bit warmer in the mid 60s with lower 60s expected over far
eastern KS.

These southerly winds will quickly increase through the morning
hours with gusts of 25-35mph likely. Expect decent warm-air
advection through the day, with afternoon high temperatures rising
into the mid 80s to mid 90s from east to west across the CWA.  Model
soundings show the deep layer of dry air remaining in place through
the day with dewpoints staying in the 50s, resulting in afternoon RH
values plunging into the mid/upper 20% range across north central
KS.  These dry conditions combined with gusty winds could result in
elevated fire danger conditions across that area.

.LONG TERM...(Thursday night through Wednesday)
Issued at 314 PM CDT Wed Sep 13 2017

By Thursday night, a positively tilted mid-level trough digs into
the Pacific Northwest while a closed low (the remnants of Irma)
located over the northeast CONUS progress eastward.  At the surface,
a surface low begins to develop in eastern Colorado early Friday
morning into Saturday increasing the pressure gradient across the
area both these days.  Expect the stronger southerly winds to be
Friday with gusts up to 30 mph possible, and up to 25 mph on
Saturday.  Both these days look to be a bit warmer than climatology,
with highs reaching into the lower 90s.

As the main upper level trough works its way over the north central
US Saturday,  a surface cold front transverses the area Saturday
afternoon and evening.  Showers and thunderstorms are expected to
develop along this front.  As for severe potential, the NAM looks
the most robust with both CAPE and shear parameters, with 0-6 km
shear values near 30kts in north central Kansas.  GFS/ECMWF remain
less enthusiastic with severe parameters, and for now, organized
severe weather looks unlikely. Precipitation may linger into early
Sunday morning.

For early next week, on again off again storm chances look likely as
models are still a bit different on the overall synoptic pattern.
The trend for warmer than normal highs continues into next week with
the upper 80s expected each day through Wednesday.  Lows will be in
the 60s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday)
Issued at 1137 PM CDT Wed Sep 13 2017

Based on updated discussion above, have included a VCTS in the
forecast for the most likely window for elevated storms. Still
looks like VFR conditions will prevail. The one exception may be
if a TS moves overhead and VSBY briefly drop down.

&&

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

$$

UPDATE...Wolters
SHORT TERM...Hennecke
LONG TERM...Heller
AVIATION...Wolters



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