Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 250851
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
351 AM CDT MON APR 25 2016

.SHORT TERM...(Today and Tonight)
Issued at 344 AM CDT MON APR 25 2016

08Z water vapor imagery shows an upper closed low over eastern SD
slowly lifting northeast. A second upper trough was moving into the
southwestern U.S. At the surface, a low pressure system was located
over eastern SD with a trailing boundary through eastern NEB and
into south central KS. Although there isn`t a lot of cold air behind
the boundary as obs show temps are still in the lower 50s behind the
front.

For today the forecast area is expected to remain in between the
upper low of SD and the deepening upper low over NV. Models show a
shortwave ridge gradually moving over eastern KS today. So there
should not be a lot of large scale forcing for precip today. However
the surface front is likely to stall over the area and become more
diffuse through the afternoon with a moist airmass remaining over
east central KS. Models continue to show some very light QPF to the
southeast of the front, and think this is more a result of the
saturated boundary layer than any forcing or lift. Because of this
have gone with a dry forecast through the day today and keep the
stratus over east central KS through much of the day. Think
afternoon temps will be cooler as a result of the moisture and
expected cloud cover over eastern KS and have lowered highs to keep
them in the lower 70s. Areas that see some sunshine (north central
and parts of northeast KS) should warm into the mid and upper 70s as
models mix the boundary layer to 850MB.

Models show a low level warm air advection pattern developing
tonight with the low level moisture returning back north. This is in
response to the upper low over the southwest approaching the central
Rockies and surface pressure falling in the lee of the Rockies. have
continued with some small POPs late in the evening and overnight
mainly because of the warm air advection pattern. Although forecast
soundings show much of the moisture being confined in the low
levels, mid level lapse rates remain fairly steep above the low
level moisture so it would not take much lift or convergence for
some possible convection to develop. Also have added a mention of
patchy fog to the forecast after midnight. Think it would not take
much moisture advection for low levels to saturate. With dewpoints in
the mid 60s already moving north through central TX and the SREF
showing reasonable probabilities for visibilities of 3 miles or
less, feel like chances good enough to add a mention. Lows tonight
should be very mild depending on how clouds and moisture move north.
So have mid 50s right along the NEB state line and lower 60s across
southern portions of the forecast area where clouds may never
scatter out.

.LONG TERM...(Tuesday through Sunday)
Issued at 344 AM CDT MON APR 25 2016

Confidence is increasing for an outbreak of severe storms across
portions of central and eastern Kansas Tuesday afternoon and
evening. Details on changes to the previous forecast follows.

Upper trough is beginning to come onshore this morning, progged to
deepen into a closed low later this evening over the Four Corners
Region. By Tuesday morning, the warm front is draped over northern
Kansas with Gulf moisture continuing to advect sfc dewpoints into
the lower 60s. Isentropic lift evident on the 300K to 310K surfaces and
overcast stratus may result in light rain showers during the early
morning, dissipating in the early afternoon as the upper trough
approaches the region. Subtle differences in the track of the upper
low remain due to the variances with a vorticity maxima wrapping
around the backside of the low over the Inter Mountain West. This has
an effect on the position of the sfc low and subsequent dryline,
now a bit further west by late afternoon. GFS at 00Z is the faster
version of advancing the dryline towards north central Kansas in
the late afternoon, triggering scattered convection initially
before expanding coverage of storms throughout the CWA through the
evening. The ECMWF exhibits feedback issues with overdoing the QPF
amounts Tuesday morning, however is similar in track with the GFS.
The NAM has trended the slowest of guidance, maintaining a strong
capping inversion over the area until shortly after 00Z before
convection develops over north central Kansas. Despite the subtle
differences, the dynamics of the system coupled with the amount of
sfc based CAPE (in excess of 3000 J/KG), minimal inhibition, and
optimal low level shear values to create an environment conducive
for severe storms. Current thinking is to see supercells form off
the dryline in the late afternoon over central Kansas before
quickly racing northeast into the area. 0-1 KM helicity values
increase to near 200 m2/s2 by 00Z enhancing the threat for
tornadoes, a few perhaps strong, in addition to the large hail and
damaging wind threat. As cells move eastward into the evening,
supercells converge into an MCS transitioning the threats to
damaging wind, large hail, and flash flooding especially in areas
that received rainfall the previous evening.

Severe threat comes to an end near midnight while the dry slot moves
in from west to east. Thunderstorms may still linger for eastern and
far northern portions of the area through Wednesday near the upper
low over southern Nebraska. Highs Wednesday drop from the middle 70s
to the upper 60s by Thursday as northwest winds advect cooler air
into the region. Shortwave ridging comes to an end by Thursday
evening as the next expansive trough over the southwest CONUS
gradually lifts pieces of energy and precipitation into the
region. Best chances for thunderstorms during this time is
currently Friday evening into Saturday as the warm front bisects
the area while the parent wave lifts overhead. Much uncertainty
still exists on locations of heaviest rainfall between guidance,
although it does appear portions of our area could see periods of
heavy rainfall.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday Night)
Issued at 1150 PM CDT SUN APR 24 2016

Cold front will be nearing the terminals in the next several hours
and bring light winds. At this point it appears the boundary will
remain north of most locations but this will allow moisture to
push northeast and will likely form MVFR cigs toward 12Z. Latest
trends seem less pessimistic with duration of cloud and with
boundary perhaps nearing area will trend this way. Could see
redevelopment by the end of this forecast but too much uncertainty
for inclusion yet.


&&

.TOP Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...Wolters
LONG TERM...Bowen
AVIATION...65



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