Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 141134
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
634 AM CDT Mon Aug 14 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 335 AM CDT Mon Aug 14 2017

Convection continues across north central Nebraska this morning near
a frontal boundary and in an area of deep moisture flux convergence.
Also noted on watervapor was a small circulation across northwest
Nebraska moving southeast. The latest CAMS show the convection
decreasing and diminishing by the time it moves into north central
Kansas early this morning. Will continue with low precipitation
chances in the north until sunrise. The frontal boundary from
northwest Nebraska into southwest Nebraska at 08Z should drift
southward through the day today into southern Nebraska late this
afternoon. Convergence along the front along with ample moisture and
instability, around 3000 J/kg of MUCAPE and about 20 to 30 kts of
shear. Convection may develop in the late afternoon or early evening
across southern Nebraska with storms then moving slowly southeast
into northern Kansas. Any strong storms will be capable of hail and
strong wind gusts as well as locally heavy rainfall. Moisture
transport vector forecasts show good moisture flux into northeast
Kansas this evening then diminishing after 09Z as the low level jet
weakens. The front in southern Nebraska is forecast to lift back
northward after 06Z in response to the upper level trough moving
into the Rockies and mid level ridge moving eastward across
northeast Kansas. Latest 06Z NAM and 00Z ARW and NMM scale back on
the convection late in the night while the GFS and ECMWF keep
precipitation over much of central and eastern Kansas. Will keep low
end chances going tonight. Highs today warm up to near 90 in central
Kansas with mid and upper 80s across the rest of the area. Lows
tonight in the mid to upper 60s.

.LONG TERM...(Tuesday through Sunday)
Issued at 335 AM CDT Mon Aug 14 2017

By Tuesday, a weak mid-level ridge will be shifting east of the area
as a mid-level trough deepens over the Pacific Northwest.  Models
continue to be in good agreement in having this trough deepen
southeastward across the Rockies through Tuesday night before the
base of the trough pivots northeastward into the north central U.S.
Wednesday into Thursday.  As the trough deepens toward the Rockies
on Tuesday, it will help to push an area of surface low pressure
over CO eastward into KS.  While models show an associated warm
front lifting northward across the CWA and further into NE on
Tuesday, there are some minor discrepancies in the timing of this
frontal passage.  This passing warm front, along with a few weak
embedded waves within the mid-level flow ahead of the trough, may
aid in the development of some scattered showers and thunderstorms
Tuesday and Tuesday night, however there are discrepancies in the
coverage of this precipitation.  As a result, have only slight to
chance PoPs into Tuesday evening.  However, have increasing PoPs
overnight into Wednesday morning and through the day on Wednesday as
the advancing trough pushes surface low pressure further eastward,
with an associated cold front tracking into north central KS by
Wednesday morning.  Models show the front slowly tracking
southeastward across the CWA through the day and finally exiting the
area Wednesday evening.  Decent southwesterly flow ahead of this
frontal passage will aid in advecting more moisture into the region,
with dewpoints reaching into the low/mid 70s across eastern KS.
Model soundings show the cap eroding away during the afternoon with
steep enough mid-level lapse rates to support 2000-3000 J/kg of
CAPE. However, models seem to be trending a bit weaker with 0-6km
bulk shear, with values reaching near 30kts.  Regardless, these
parameters may be enough to support the development of some
organized convection Wednesday afternoon into Wednesday evening.
While some strong to severe thunderstorms may be possible, this
severe potential may be very dependent upon how the atmosphere is
affected by the Tuesday night/early Wednesday AM convection. Some
locally heavy rainfall will be possible as PWAT values of at least 2
inches are expected.  As the cold front and mid-level trough
progress east of the area, expect dry conditions on Thursday before
additional scattered chances for showers and storms potentially
return for Thursday night through the weekend. There are significant
model differences in the depiction of the mid-level pattern, so have
low confidence in the PoP forecast beyond Friday night.

Despite the mid-week frontal passage, temperatures look to remain
fairly steady with highs in the mid/upper 80s with low temperatures
in the mid 60s to low 70s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 634 AM CDT Mon Aug 14 2017

IFR cigs have formed with low level moisture return this morning.
Expect the cigs to gradually lift to MVFR by 16Z-17Z then VFR
after 18Z. Convection expected to remain to the north of the
terminals this morning and confidence is low in timing later
tonight so left mention of TSRA out of forecast for now. Winds
south near 10 kts.

&&

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

$$

SHORT TERM...53
LONG TERM...Hennecke
AVIATION...53



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