Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 280849
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
349 AM CDT Thu Aug 28 2014

.SHORT TERM...(Today and Tonight)
Issued at 345 AM CDT THU AUG 28 2014

Upper trough was progressing across the Rockies this morning. A lead
shortwave was moving across south central Nebraska while another was
rounding the base of the trough and moving into southeast Colorado.
Water Vapor Satellite loop shows plume of moisture from the eastern
Pacific into the Central Plains feeding the MCS ongoing in Nebraska.
Showers and isolated thunderstorms have developed in the moisture
axis from south central Kansas into north central Kansas.
Precipitable water values continue to be near 2.00 inches from
central Kansas into southwest Iowa and remain in place through
tonight. Short term models indicate that scattered thunderstorms
will continue across much of north central into northeast Kansas
through mid morning gradually spreading eastward and weakening
through late morning. Expect a lull in precipitation from late
morning into early afternoon, then increasing through the afternoon
and evening hours as forcing for ascent increases as the upper
trough moves out into the Central Plains. Frontal boundary across
western Kansas will gradually work its way into north central Kansas
late tonight. Expect scattered thunderstorms this afternoon to
become more widespread tonight across the CWA. Good moisture
transport will lead to high rainfall rates. The heavy rainfall may
lead to localized flooding or flash flooding tonight, especially in
areas of far northeast Kansas. Clouds will limit warming today with
most areas in the north only reaching the mid 80s while areas
southeast of the turnpike will be in the lower 90s. Tonight lows
fall into mid 60s in north central Kansas to around 70 in northeast
and east central Kansas.


.LONG TERM...(Friday through Wednesday)
Issued at 345 AM CDT THU AUG 28 2014

An unsettled weather pattern will persist through much of the
extended forecast as several systems are expected to track across
the region.

By Friday morning, the mid-level trough that is currently located
over the Rockies will have progressed eastward, becoming centered
over the Northern and Central Plains. This advancing trough will
help to push the area of low pressure currently over the High Plains
eastward, with the associated cold front progged to move into
central Kansas by Friday morning. Latest model runs are in fairly
decent agreement with each other in having this trough transition
from a closed low to an open wave, which will slowly track eastward
over the region Friday and Friday night before lifting northeastward
toward the Great Lakes region. With this slow-moving system, the
cold front is not expected to exit east of the forecast area until
Saturday morning. The combination of modest frontogenetical forcing
and good moisture advection should help to produce more widespread
showers and thunderstorms Friday and Friday night. There may be
upwards of 1000-2000 J/kg of CAPE in place, however 0-6km bulk shear
values look to remain low at 25kts or less. As a result, severe
weather is not expected but cannot rule out some strong gusty winds
with the strongest storms. The primary concern with this activity
though will be the potential for locally heavy rainfall as PWAT
values range from 1.6-1.9 inches. Some locations across the forecast
area (particularly across portions of north central and far northern
Kansas) have already received several inches of rain from recent
scattered thunderstorm events, so these locations may be more
sensitive to localized flooding concerns as well. Models are in good
agreement in having the trough well northeast of the area by
Saturday morning, so have gone with a dry forecast for Saturday.
Have continued to trend a bit cooler with temperatures on Friday
(highs in the mid 80s) due to the extensive cloud cover and the
effect of rain-cooled air from the widespread precipitation.
However, with this precipitation expected to end by Saturday with
skies becoming mostly sunny, have trended warmer for Saturday high
temperatures (mid/upper 80s).

Surface high pressure will move into the region on Saturday behind
the exiting system. However, the dry conditions will be brief as
models show another mid-level trough moving into the Pacific
Northwest by Saturday and quickly deepening across the northern and
central Rockies on Sunday. This advancing trough will help to push
another cold front through the forecast area Sunday night into
Monday morning. Ahead of this front, weak embedded shortwaves are
expected to develop across Kansas and Nebraska Saturday night into
Sunday and will be accompanied by a strengthening low-level jet.
Collectively these ingredients will help to support scattered
thunderstorm activity with better precipitation chances focused near
the Kansas/Nebraska border by Sunday. PoPs increase Sunday night
into Monday morning with the frontal passage as additional
widespread showers and thunderstorms are expected. With modest
instability and decent 0-6km bulk shear in place, some of these
storms may be strong to severe. Locally heavy rainfall and localized
flooding will be a concern once again with this system as PWAT
values may be upwards of 1.8-2.0 inches. Models are in decent
agreement in having the precipitation end from west to east through
the day on Monday. However, they suggest that the front may get hung
up just south of the forecast area and potentially lift further
northward Tuesday into Wednesday, which could support the
development of scattered showers and thunderstorms north of this
boundary Monday night through Tuesday night. However, there is still
a great deal of model uncertainty this far out, so kept PoPs low.
With regards to temperatures, expect a brief warm-up (near 90
degrees) on Sunday ahead of the frontal passage, with slightly
cooler temperatures through the first half of next week as highs
drop into the 80s and lows cool into the 60s.

&&

.AVIATION...(For the 06Z TAFs through 06Z Thursday Night)
Issued at 1144 PM CDT WED AUG 27 2014

Will continue with a dry and VFR forecast for TAFS but also
kept VCTS with the terminals in the 08Z-13Z timeframe as the
North Central KS MCS passes/backbuilds just north of the area.
Will steadily veer winds from easterly to southeast by 10z and
leave thru the day with the expectations that an outflow boundary
will keep somewhat of a more easterly component to the winds
through the day.


&&

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

$$

SHORT TERM...53
LONG TERM...Hennecke
AVIATION...63






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