Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 281149

Area Forecast Discussion
National Weather Service Topeka KS
649 AM CDT Fri Apr 28 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 308 AM CDT Fri Apr 28 2017

Mid level shortwave trough is currently lifting over northwest KS and
southwest NE with the axis extending over the forecast area. Showers
have developed as a response to this increased lift, which is also
aided by a strong low level jet. It appears there is enough moisture
and steep lapse rates for some isolated thundershowers to develop.
The latest RAP forecast shows an area of up to 600 j/kg will spread
northeastward through late morning. It is possible that a few of
these storms may be capable of producing small hail. By late morning
the lift will most likely move north of the area as the trough
rotates back towards the Rockies, and therefore most locations dry
out. A weak surface low pressure has developed over southwest KS and
it will migrate across eastern KS later today. As a result a warm
front sets up somewhere in between I-70 and the NE state line. Winds
south of the front will shift to the south, but during the evening a
cold front pushes through behind the departing surface low pressure.
North of the warm front easterly flow keeps the stratus in place
while mixing south of the front may allow for some breaks in the
clouds. As a result high temperatures today range from the lower 50s
in far northern KS to near 70 along and south of I-70. Late tonight
a strong mid level low pressure begins to lift out over the southern
plains. Convection is expected to develop along and north of the
front that pushes through the area during the evening. Model
consensus is that this surface front reaches far southeast KS or
northeast OK before becoming quasi-stationary. Expected an area of
rainfall to spread over the area late tonight with the highest
amounts falling in southeast KS. This rainfall looks to continue
after sunrise tomorrow morning. With the impressive moisture
transport northward elevated instability may build over east
central KS so thunder will be possible with better chances closer
to the surface front.

.LONG TERM...(Saturday through Thursday)
Issued at 308 AM CDT Fri Apr 28 2017

Focus is on the anomalous upper trough and associated impressive
synoptic set up for heavy rains across the region over the
weekend. 00Z models that show best clustering remain the ECMWF and
UKMET along with the GFS which all suggest that deep convection
will occur in the vicinity of the sfc boundary across northeast
OK and southwest MO. Fri night into early Saturday and that is the
scenario we still expect to develop. The NAM is the odd model out
with little in the way of deep convection along the sfc front and
instead it focuses precip along the 850mb boundary which is over
northeast KS. The NAM also suggests a stronger small scale 700mb
circulation across KS which in turn causes higher rainfall amounts
across eastern/central KS as compared to the global models. We
have to also mention that the GFS has displayed a subtle trend
northwest with the axis of heavy rains over the past couple of
days and given the very strong upper ridge which will develop
across the eastern US it would make sense that the stronger
moisture transport could become focused northward into parts of
southeast and east central KS Sat into Sat night. Bottom line...a
slow moving intense storm system will bring the potential for
widespread 2-3 inch rains to the area beginning early Saturday and
lasting through Sat night. By Sunday as the upper system
approaches and continued upper divergence and increasing dynamic
lift develop expect the deformation zone precip to become
established across central/northern KS with a potential dry slot
across the rest of the area. At this time we still believe that
the axis of heaviest rains i.e. more than 4" should remain
southeast of the CWA but trends need to be watched for any
continued NW shift of heaviest rains.

The upper trough will drift over the area Sunday night keeping
the deformation precip ongoing across central and north central
KS. There could be some wet snow mixed in for a time across far
north central KS Sun night but do not expect any accums or impacts
from snow at this point. Any severe weather threat should also
remain southeast of the CWA with this system on Sat. This appears
to be a heavy rain event with potential impacts to area
creeks/rivers which could end up in flood come Sunday into early
next week.

If there is any good news related to the extended forecast it is
that the risk for heavy rains will not return through next week
with troughing across the central U.S. through mid week with some
low chcs for scattered precip followed by dry and mild conds for
the end of the week.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 627 AM CDT Fri Apr 28 2017

Scattered showers are expected to continue for the next few hours.
Each shower may cause the ceilings to lift to VFR otherwise the
ceilings should be borderline IFR. Later today mixing and heating
should cause the ceilings to lift, but these heights are
uncertain. Also, the latest RAP soundings are showing the clouds
may scatter out for a brief period this afternoon. Stratus is
expected to build later this evening behind a surface low
pressure. Another sound of showers moves in mainly after midnight.




SHORT TERM...Sanders
AVIATION...Sanders is the U.S. government's official web portal to all federal, state and local government web resources and services.