Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 281142
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
642 AM CDT Thu May 28 2015

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 353 AM CDT THU MAY 28 2015

Convective complex that began over western Kansas this afternoon had
recent central portions of the state early this morning. System is
making decent eastward progress and duration of heavy and then
lighter precip are not long, helping keep heavy amounts in check.
Precip will likely be waning in next few hours and expect the Flash
Flood Watch to expire, if not be cancelled early. Another somewhat
stationary complex has taken shape over southwest Kansas over the
past few hours, perhaps from gravity wave from MCS to its south.
Even the rapidly updating models are struggling with these smaller
scale systems, leading to a rather low confidence forecast.
West-southwest flow remains aloft with at least three shortwave
troughs over the western states evident on water vapor imagery.

HRRR and RAP continue to be slow with the current complex in the
CWA, and seem to attempt to congeal the SW KS system into the current
one over the next several hours. Going with radar trends, expect a
decreasing trend in the west with eastern areas seeing the current
bands move through early this morning. A general downtrend in
activity is then expected into the afternoon with next better chance
for convection coming in the late evening and overnight as the upper
wave over Utah early this morning swings through. With persistent
but modest warm air advection into the region and outflow
boundaries, gravity waves, and other mesoscale forcing mechanisms
likely passing through, at least small precip chances exist
throughout the day and night. Elevated instability tonight looks
somewhat greater than today with a similar though more veered low
level jet. Along with PW values around 1.5", will again need to
watch for heavy rains, but confidence is too low to support a Flash
Flood Watch with wide spread in where and even if precip will occur.

.LONG TERM...(Friday through Wednesday)
Issued at 353 AM CDT THU MAY 28 2015

By Friday morning the main mid/upper level trough stretches from
eastern WY up to MN, while several shortwaves swing over the central
and southern plains. These waves will likely dictate where showers
and storms develop and or track during the day Friday. A cold front
will then approach the area from the west bringing higher dew points
in from the south. Both the NAM and GFS are suggesting dew points
reach the mid to upper 60s with a few 70s possible. Decent lapse
rates in the southwest flow aloft yield cape on the order of
2500-3500 j/kg with little inhibition. The deep layer shear is
around 20 kts, and the vertical profile seems mostly unidirectional.
Given this type of environment both ahead and along the front do not
expect any supercells. If any of these waves or MCSs pass over
during the morning hours than subsidence could inhibit diurnal
development. The cold front should begin to slide through beginning
Friday evening and during the overnight. Showers and storms are
possible along the front, but the instability should be on the
decrease and shear remains low. So again do not expect any well
organized severe storms overnight. Also, the models are not in good
agreement on the 0-3 km bulk shear magnitudes and directions, so not
sure if there will be any organized wind threat. Although, given the
cape there is a marginal risk for hail during the afternoon and
evening hours.

The front should clear the area by 12Z Saturday, but the problem is
the mid level trough is still back over central KS and eastern NE.
The trough is forecast to progress eastward during the day Saturday.
This along with 925 mb frontogenesis could provide enough lift
within some residual low level moisture for light post frontal
precip. Confidence in these precip chances are not high therefore
kept the area mostly under slight pops. Cooler and drier air moves
in on Sunday as an upper level ridge builds across the southern
Rockies. The models have now kept the energy that moves over
Saturday closed off over the southern MS valley preventing the ridge
from building too far north. Meanwhile more mid level troughing
moves over the Pacific northwest and northern Rockies by mid week.
Southwest flow aloft will soon follow as more shortwaves begin to
drive the weather.

&&

.AVIATION...(For the 12Z TAFs through 12Z Friday Morning)
Issued at 641 AM CDT THU MAY 28 2015

Precipitation should slowly subside over the next few-several
hours with wave pushing off to the ENE. Next best chance for
convection comes after 03Z with another complex of TSRA possibly
moving through from the west. Will maintain VCTS only at this
point given continued uncertainty.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH until 7 AM CDT this morning FOR KSZ008-009-
020>022-034>037.

&&

$$

SHORT TERM...65
LONG TERM...Sanders
AVIATION...65





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