Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 191659
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1159 AM CDT Fri May 19 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 334 AM CDT Fri May 19 2017

An intense upper level trough was located over western CO with a
trough axis extending southward along the AZ and NM border. This
upper level trough will lift northeast across western KS this evening,
then north-northeast into southeast SD by Saturday afternoon.

At 2 AM, a surface analysis showed a nearly stationary cold front
extended from extreme southeast NE, southwest across the CWA,
from just east of Sabetha, to east of Manhattan to north and west
of Wichita. An outflow boundary was located along OK and KS
border, south of Wichita and extended east-northeast across
extreme southeast KS.

Today and Tonight, most high resolution models show this OFB lifting
northward through the mid and late morning hours to north of I-70
and the stationary front may shift slightly west to the south of I-
70. As the southerly 850mb winds strengthen, deeper gulf moisture
will advect northward across the southern and eastern counties of
the CWA, to the southeast of the surface stationary front. The
HRRR and WRF models show a broad area of elevated thunderstorms
developing across southeast KS during the mid and late morning
then tracking north-northeast across the southern and eastern
counties of the CWA. This cluster of thunderstorms, if they
develop, may become strong to severe with the primary hazard being
large hail and heavy rainfall, and if they become surface based a
damaging wind gust potential. This cluster of storms may shift
northeast of the CWA by 20Z. The HRRR shows there could be enough
outflow to shift the OFB back to the south, just south of the CWA
by 22Z. Discrete supercell thunderstorms may begin to develop
across south central KS along the front and to the north of the
OFB. The OFB may then surge back northward across the southeast
counties, while discrete supercell thunderstorms across south
central KS congeal into line segments or a larger QLCS and move
northeast along the stationary surface front. The 6Z NAM, 6Z RAP
and 00Z GFS show between 1500-2500 J/kg of MLCAPE along and
southeast of the stationary front, generally along and southeast
of the KS turnpike then northeast into Jefferson county. Strong
southwesterly mid level flow of 50 to 60 KTS will result in the 0-
6km effective shear to be in the 40 to 50 kt range, sufficient
for updrafts with mid-level rotation, given the instability
forecasted. The big question will be the mode of convection. If
discrete supercells can remain scattered and move northeast
parallel along the stationary cold front then there may be a
better chance for isolated tornadoes, especially for areas
southeast of the KS turnpike, where 0-1 KM SRH will be in the
150-200 J/kg range. If the boundary shifts southeast across east
central KS during the late afternoon, like the 06Z NAM suggest,
then the better chances for isolated tornadoes will be across the
southeast counties of the CWA. If storms congeal into line
segments or QLCS, then the risk for tornadoes is smaller unless
meso vortices develop within the QLCS and the better chances for
this to occur will be along or southeast of the surface front. The WRF
solutions show a larger QLCS developing across the central
counties of the CWA during the early evening, then spreading east
across the northeast and east central KS during the remainder of
the evening hours. The primary hazard will be damaging winds and
large hail in any embedded updrafts rotate. Heavy rainfall with
an additional 1 to 3 inches will be possible Today and Tonight. I
will keep the flash flood watch going through 12Z SAT for the
entire CWA. Though the best chance for flash flooding will be
across the eastern two thirds of the CWA.

.LONG TERM...(Saturday through Thursday)
Issued at 334 AM CDT Fri May 19 2017

Saturday will dry with cooler temperatures in the upper 50s across
north central KS to the mid 60s across east central KS. Skies will
begin to clear from northwest to southeast across the area.

An upper trough will dig Southeast across northern high plains into
the southern plains Sunday through Tuesday. There may be enough
residual moisture return ahead of a surface front for showers and
thunderstorms to develop Sunday afternoon into Sunday night. There
may be shower and elevated thunderstorm chances behind the surface
front through Tuesday as the upper level trough amplifies across
the plains and phases with an upper low across the upper midwest.
Highs may warm slightly into the lower 70s on Sunday but cool into
the mid to upper 60s by Tuesday.

The remainder of the week will be dry as northwesterly mid-level
flow becomes zonal by next Friday. Highs will warm into the 70s on
Thursday with near 80 degrees by Friday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1158 AM CDT Fri May 19 2017

Ceilings have been varying widely this morning, although MVFR/IFR
have been predominating over TAF sites. A line of thunderstorms is
expected to move through sites mainly between 19-23Z, before
scattered showers and storms continue through the evening hours.
Conditions do not improve much by morning with precipitation
ending near 12Z, but MVFR ceilings lingering until the end of the
period.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Saturday morning for KSZ008>012-
020>024-026-034>040-054>056-058-059.

&&

$$

SHORT TERM...Gargan
LONG TERM...Gargan
AVIATION...Heller



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