Area Forecast Discussion
Issued by NWS Topeka, KS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KTOP 052049
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
349 PM CDT Tue May 5 2015

.SHORT TERM...(This Evening through Wednesday)
Issued at 347 PM CDT TUE MAY 5 2015

High cloud rather plentiful across the Central Plains into the Great
Lakes today, downstream of an upper trough rotating northeast out of
the Southern Rockies. Light to moderate showers rather have been the
rule in western portions of the state with thunderstorms quite
limited with very poor mid level lapse rates. Isolated showers and
thunderstorms have developed in daytime heating to the south and
east and a few of these could impact adjacent areas of the CWA in
the next few hours.

Rainfall still anticipated to translate north and east with time this
evening into Wednesday morning as the primary forcing aloft pushes into
central and eastern Oklahoma and moves on northeast into increasing
PW airmass of around 1.5" (near record levels for early May).
Instability quite hard to come by as lapse rates change little,
though low levels will be well fueled by 850mb south winds around
50kt and dewpoints in the 10-12C range. Have backed off thunderstorm
expectations and not quite as concerned about heavy rains. Any
focusing of higher rates near yesterday`s swath of rain will need to
be monitored, but flash flood guidance in around 1"/hr and 2"/6hr
seems unlikely to be met. There remain some differences on timing of
both onset and end to this precip, and this of course impacts
Wednesday afternoon`s expectations. Currently expect some drying to
occur in western locations by early afternoon though how much
insolation can occur is uncertain as south winds increase for
continued moisture influx. Storms may fire in southwestern portions
of the state in the afternoon as another wave rotates into this
area, and there is some potential for these to reach the north
central Kansas in subsequent hours. CAPE/shear parameters could be
enough to support severe weather but not much confidence in timing
or destabilization.

.LONG TERM...(Wednesday Night through Tuesday)
Issued at 347 PM CDT TUE MAY 5 2015

Models continue to generate precip Wednesday night when it appears
the longer wavelength trough is lifting north into NEB. Conceptually
one would expect subsidence behind the wave and an end to precip.
However the models have been consistent in showing convection
redeveloping Wednesday evening mainly along the NEB state line.
There appears to be a subtle wave in the 700MB pattern along with a
weak PV anomaly that lifts from the TX panhandle into northeast KS
through the evening. So there may be some energy that wraps around
the back side of the upper wave that helps to generate precip
Wednesday evening. The NAM is strongest with the forcing than the
other models, hence it`s better signal for precip in the QPF prog.
Nevertheless with some consistency in the signals, have trended POPs
along the NEB boarder up while keeping a chance further south. Deep
layer shear and instability do not look all that impressive and
given a lack of surface feature to focus rainfall, excessive
rainfall appears to be a low probability through the night. Think
Thursday may see a break in precip as this forcing lifts northeast.
However left some likely POPs in across far northeast KS to account
for any lingering morning activity and to blend with neighboring
offices. Lows Thursday morning should be very mild on account of a
strong pressure gradient keeping the boundary layer well mixed and
skies likely remaining overcast. Winds are expected to remain in the
15 to 25 MPH range overnight, so have lows in the lower and mid 60s.
Highs are forecast to be in the mid 70s based on the model progs of
850MB temps. However is the sun is able to break out, temps could be
a little warmer.

Think Thursday night and Friday morning may be a better time for
convective rainfall and possible flash flooding as the models bring
a weak boundary into the area. This should provide some focus for
low level moisture convergence and persistent deep moist convection
as another vort max lifts out from the southwest. The boundary is
not very strong and forecast to move through slowly increasing the
likelihood that heavy rain is able to setup over a location for an
extended period of time. Confidence is about average since the
forecast is based on smaller scale details that have a tendency to
be variable. There should be more of a gradient in temps for Friday
with a wind shift and weak cold air advection moving into north
central KS. Therefore have lows ranging from the mid 50s in north
central KS to the lower 60s across southeast KS. Highs are likely to
be held down by cloud cover and northerly winds across the north
where lower 70s are forecast. East central KS may hang onto a
southerly wind so highs are expected to be a little warmer in the
mid 70s.

Heading into the weekend, there looks to be a very good chance of
convection each day as the upper level closed low over the Desert
Southwest finally deepens and begins to rotate out into the
Southern and Central Plains by Saturday night. Saturday looks to
have the better ingredients for the overall severe weather threat
with the negatively tilted trough over the southwest KS into OK.
With good WAA and bringing in higher theta-e values along with
better shear and CAPE this could be the last main threat this
particular system brings to the area. Both the EC and GFS are in
close agreement to this point. Into the day on Sunday and into
Monday morning there seems to be the largest spread on timing with
the two solutions. The EC wants to absorb the upper level low into
the northern branch of the polar front jet as it lifts into
Nebraska. The GFS, on the other hand, wants to attempt to do the
same, but is slower to do so and wants to occlude the system into
the longer wave trough over the Northern Plains. If this scenario
plays out, it could cause some lingering precip over the northern
parts of northeast KS, but shouldn`t last long into Monday if this
is the case.

&&

.AVIATION...(For the 18Z TAFs through 18Z Wednesday Afternoon)
Issued at 1245 PM CDT TUE MAY 5 2015

Have attempted to provide more detail on expectations, but
confidence in timing and impacts is not high. Could easily see
visibilities drop to IFR in heavier convection but well too much
uncertainty in timing that. Winds will likely diminish a bit around
01Z at TOP and FOE.


&&

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

$$

SHORT TERM...65
LONG TERM...Drake/Wolters
AVIATION...65






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.