Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 042344
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
644 PM CDT Mon May 4 2015
...Update to aviation forecast discussion...
.SHORT TERM...(This Evening through Tuesday)
Issued at 334 PM CDT MON MAY 4 2015
Subtle upper level waves continue to impact the forecast, with at
least one feature centered over central Nebraska early this
afternoon. Appears recent line of convection in MHK vicinity
resulted from lift with this wave. Front remains rather stationary
from near GCK to near FNB with pressure rises and falls flanking it
per 19Z objective analysis though convergence along it rather weak.
Dewpoints to around 60F and decent mid level lapse rates leading to
little convective inhibition for surface-based storms with CAPE near
1500 J/kg on the warm side of the front.
Short-range models again struggling with precip timing/location,
though not terribly surprising in this complicated regime.
Frontogenesis rather weak and not much obvious increasing mechanism
leads to lower than normal confidence in widespread convection along
the front. Could even see radar trends diminishing near it in the
next few hours as the Nebraska wave slowly moves off. Bottom line to
next few hours is a mid-range PoP forecast and will need to watch
for development across much of the area along and N of I-70 with
hail up to 1.5" and winds gusts near 60 mph the main concern in
modest shear. Model soundings rather similar with CAPE toward
"skinny" variety with mean flow vectors along the front for some
training/heavy rain potential. For overnight trends, south flow
taking hold well into the Northern Plains should help mix the front
north tonight, though short-range models have also been similar with
outflow sinking south into east central Kansas into the evening.
Have spread small PoPs south in kind with decreasing trends after
06Z. Drier air in the mid levels remains to be anticipated for the
central lesser concern for another day of elevated precip. There
remains a small indication for isolated storms into east central
Kansas where capping falls off in the afternoon and ahead of the
next wave in the west.
.LONG TERM...(Tuesday Night through Monday)
Issued at 334 PM CDT MON MAY 4 2015
Models continue to show a wet pattern for Tuesday night through
Sunday, and so there is little change from the previous forecast
in that there are chances for showers and thunderstorms through
the weekend. The better chances looks to be late Tuesday night and
Wednesday morning. There is good agreement in a well defined
shortwave lifting out across the central plains. This forcing
combined with little inhibition to deep moist convection is
expected to generate widespread precip. Initially Wednesday
morning deep layer shear is on the weak side with modest
instability. Therefore the main impact expected from these storms
is localized heavy rain. If skies can clear out and insolation
increase instability, the shear is progged to increase later in
the day. However think if this is to occur, it is more likely to
be along the dry line across southwestern KS.
Precip chances persist Wednesday night through Saturday as
southwest flow continues to bring vorticity maximum across the
area. Timing these features is a bit tricky so it is hard to get
to excited about raising POPs. Generally have kept chances for
rain in the 40 to 60 percent range.
Saturday night and Sunday may see the next better organized wave
lift out with the closed low. There remains some differences in
the model solutions with the track of the upper low and how much
energy comes out from the southern plains or whether the bulk of
vorticity remains to the west of the forecast area. With the
models showing deep layer shear increasing with the wave, there is
the potential for some organized severe storms. However this is
still a ways out and confidence in the details, especially the
timing of when storms are more likely, is low.
Finally the closed low kicks out Sunday night with cooler and
dryer air moving in for Monday. This should be the first
opportunity to begin drying out.
With little change in airmass, temps are expected to remain fairly
persistent through the weekend with lows around 60 and highs in
the mid 70s to near 80. The main question with temps is whether
there will be a period of insolation that allows temps to break
out or if cloud cover and precip keep temps cooler. Wednesday
still looks like the cooler day of the week anticipating clouds
and precip for much of the day. Temps trend cooler Sunday night
and Monday as cold air advection increases from the northwest.
.AVIATION...(For the 00Z TAFs through 00Z Tuesday Evening)
Issued at 636 PM CDT MON MAY 4 2015
Ongoing thunderstorms look to persist for the next few hours and
possibly linger as late as 06Z. The coverage near MHK is much
greater than the TOP/FOE area therefore kept VCTS at TOP/FOE and
TSRA at MHK as prevailing for now. There could be brief periods of
MVFR/IFR within the heavy rain cores. The rest of period should
remain VFR after the storms tonight.