Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 212338
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
638 PM CDT Mon Apr 21 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Tuesday)
Issued at 349 PM CDT MON APR 21 2014

Water vapor imagery showed the mid-level trough associated with
today`s passing system progressing east of the area toward the Ohio
River valley with a mid-level ridge developing over the Rockies. At
the surface, the cold front that had tracked southeastward over the
region today was situated over far southeast Kansas at 20z. A few
scattered showers that were still developing across eastern Kansas
behind the front within a narrow band of low-level lift, but this
activity is expected to diminish and exit east of the area by late
this afternoon. Surface high pressure situated across the High
Plains was quickly advancing into the area behind the exiting
system, resulting in a bit of a pressure gradient setting up over
central Kansas, which contributed to northerly winds gusting upwards
of 20-30mph this afternoon. This advancing surface high was also
resulting in cloud cover quickly diminishing behind the front across
most of western and central Kansas, with afternoon highs peaking
into the mid/upper 70s over north central Kansas. Lingering cloud
cover over far east central Kansas kept temperatures a bit cooler in
the upper 60s/low 70s.

Winds will quickly diminish this evening as the surface high
progresses further eastward across the region, with models showing
the surface high centered over the cwa by Tuesday morning. In
addition to light winds, this advancing surface high will also result
in mostly clear skies and decent radiational cooling with low
temperatures dropping into the 40s.

The mid-level ridge will continue to track eastward into the central
U.S., which will help to push the surface high east of the area and
cause winds to gradually veer toward the east and southeast through
the day. Soundings show a few mid-level clouds developing through
the day, but otherwise conditions will be mostly sunny with
afternoon high temperatures reaching into the low/mid 70s. Dry
conditions are expected through the day with dewpoints in the 30s to
low 40s. As a result, RH values may drop into the mid-20 percent
range over north central Kansas, but winds should not gust more than
15-20mph across that area during the afternoon, so do not anticipate
any fire weather concerns at this time.

.LONG TERM...(Tuesday Night through Monday)
Issued at 349 PM CDT MON APR 21 2014

Tuesday Night and Wednesday Morning, An intense upper level trough
across the western conus will move into the high plains late
Wednesday afternoon. A lee surface cyclone will deepen across
eastern CO through Wednesday afternoon. The tightening pressure
gradient at both 850 MB and the surface will transport deeper
moisture north across the southern and central plains. As the
deeper moisture advects northward into central KS...isentropic
lift will cause scattered elevated thunderstorms to develop across
the CWA after midnight Thursday. The stronger isentropic lift
ahead of the deeper moisture return will shift northeast of the
CWA during the mid an late morning hours of Wednesday.

Wednesday Afternoon and Wednesday Night, The warm sector on
Wednesday afternoon will probably remain capped for much of the CWA.
As the H5 trough moves east into the high plains a surface front
and dryline will move east into western KS. Surface convergence
ahead of the surface cold front moving southeast across northwest
KS and the dryline moving east across west central and southwest
KS, along with stronger ascent ahead of the H5 trough, will cause
numerous thunderstorms to develop along the the cold front and
southward along the dryline by 20Z WED. It looks like the gulf should
reach equilibrium by Wednesday but the true deep gulf moisture
will only reach central TX. Modified Gulf moisture...with dewpoints
in the mid to upper 50s will advect northward across central KS
during the day. MLCAPES look to be around 1500-2000 J/KG across
west central KS and given that temperature and dewpoint
temperature depressions will be about 25 to 30 degrees, higher
based storms should develop. The Effective vertical wind shear
between 0 and 6 KM will increase to 30 to 50 KTS across central KS
late Wednesday afternoon. Initially thunderstorms may develop as
high based discrete supercells with a large hail and damaging wind
hazard. The higher LCL`s may preclude tornado development with any
supercells across central KS. As the cold front occludes the
dryline and the ascent ahead of the H5 trough increases the
isolated to scattered supercell thunderstorms will congeal into a
squall line during the late afternoon and evening hours and push
east into north central KS. A squall line or QLCS will cause
damaging wind gusts, hail and brief heavy rainfall. The line of
storms will move east across the remainder of the CWA after
midnight. The MUCAPE looks to drop to 500 to 1000 J/KG across the
central and eastern CWA. The main hazard may be strong gusty
winds, which may reach 60 MPH in some locations along with nickel
to quarter size hail and brief heavy rainfall. The vertical
windshear may increase as the LLJ increases across the western CWA
after 00Z. If the QLCS is intense enough while moving through the
western counties of the CWA during the evening hours, then
mesoscale vortices may develop along the line and enhance the RIJ
or perhaps even cause a few small brief rain wrapped tornadoes
within the line of storms.

Highs on Wednesday will warm into the upper 70s to lower 80s ahead
of the line of storms. South winds will increase to 20 to 35 MPH
with gusts of 30 to 45 MPH during the late morning and afternoon
hours.

Thursday, the cold front will move southeast of the CWA during the
morning hours. Lingering showers and thunderstorms will push
southeast of the CWA by early afternoon. Skies will clear from
northwest to southeast across the CWA during the afternoon hours.
Northwest winds will bring in a slightly cooler airmass with highs
in the lower to mid 70s.

Friday, An upper level trough will amplify across the Great Lakes
States and cause a stronger cold front to move southward across the
Central Plains. The front will begin to move south across the
northern counties of the CWA during the early afternoon hours. Highs
along the NE border may only reach the upper 60s, while highs across
the southern counties will reach the mid to upper 70s with southwest
to westerly winds ahead of the surface cold front. The front will
move southward across the CWA as a dry front to to a lack of
moisture and an upper level ridge amplifying across the plains.

Friday Night, the cold front will stall out across southern KS as
a lee surface cyclone deepens across southeast CO. Southerly 850
MB winds will advect deeper gulf moisture northward into eastern
KS. Isentropic lift over the surface front will cause elevated
thunderstorms to develop. These elevated storms may become severe
late Friday night as southwest flow aloft increases to 30 to 40
KTS and the LLJ increase to 40 KTS. The resulting vertical
windshear combined with increasing MUCAPES near 1,000 J/KG may
cause some of the elevated thunderstorms to rotate and produce
large hail during the morning hours of Saturday.

Saturday will be an interesting day across the southern plains. A
strong negative tilt H5 trough will lift northeast out of the four
corners region. The surface front along the KS and OK border will
begin to lift north as a warm front. The warm front should remain
south of the CWA through Saturday afternoon as the surface low
moves east-northeast across south central KS. Supercell
thunderstorms will most likely develop from the triple point near
Medicine lodge...southward along the dryline across western OK.
The stronger shear and moderate CAPE may cause tornadic supercells
to develop in this area. However, storms north of the warm front
across the CWA will be elevated and may cause large hail as the
vertical windshear north of the warm front will be strong enough
for rotating elevated updrafts. Some of the area may see heavy
rainfall, especially if elevated thunderstorms train over the same
areas.

Saturday night into Sunday, the intense upper level trough will
lift northeast across the plains. The 12Z ECMWF shows the surface
low and warm front moving northeastward across east central KS
during the night. The GFS and GEM show more of vertically stack
system with the surface low remaining stationary across southeast CO
and a cold surface ridge building southward across the the mid MS
river valley which will cause the boundary across southeast KS to
push southward a s warm front. Both models show the best chance for
elevated thunderstorms to be north of the boundary. If the ECMWF
were to verify the better rain chances will be across the the
northern counties of the CWA. The GFS and GEM would have good
thunderstorm chances across the entire CWA. The ECMWF looks to have
the higher MUCAPES and vertical windshear, which would provide a
better chance for severe elevated thunderstorms Saturday through
Sunday morning. Some areas of the CWA may have flooding problems
with a prolong period of heavy rainfall possible. The Thunderstorm
chance should end Monday afternoon as the 850m

Sunday, A strong cold front will move southeast across the CWA.
Thunderstorms may redevelop along the cold front to the southeast of
the CWA. Light rain will continue north of the cold front through
into Monday. Highs will cool into the 60s on Sunday and 50s on
Monday. If skies clear Monday night, there may be a chance for frost
and or a hard freeze.

&&

.AVIATION...(For the 00Z TAFs through 00Z Tuesday Evening)
Issued at 637 PM CDT MON APR 21 2014

VFR conditions anticipated in quite dry airmass working in from
the north. Main issue is winds which will slowly veer through the
period. Some higher resolution models suggest north winds around
30 kts developing in the 500-1000 ft agl layer for much of the
first portion of the forecast and will monitor trends for possible
wind shear inclusion.

&&

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

$$

SHORT TERM...Hennecke
LONG TERM...Gargan
AVIATION...65





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