Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 152047
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
347 PM CDT Wed Apr 15 2015
.SHORT TERM...(This Evening through Thursday)
Issued at 347 PM CDT WED APR 15 2015
20Z water vapor imagery shows a closed low over eastern UT. A weak
vort max was rotating north into the NEB panhandle while a second
vort max moved across northern AZ. Additionally the elongated area
of vorticity responsible for the light showers this morning across
far eastern KS continues to lift north and east of the area. At the
surface, an area of low pressure has remained nearly stationary over
the CO high plains while high pressure remains over the Great Lakes.
This pattern favors the continued moisture advection from the
southeast as dewpoints have gradually risen today.
For tonight, models hint at the vort max over AZ lifting north
through western KS. In response the low level jet briefly increases
theta-e advection with some isentropic lift. Mid level lapse rates
steepen up to around 8C/km. With this in mind think there is a
chance for elevated convection late tonight. This activity could
develop to the west of the forecast area and move into north central
KS prior to dawn. Since deep layer shear is fairly weak, I don`t
anticipate storms being much more than regular thunderstorms. The
ECMWF is not quite as ambitious with the elevated precip as the NAM
and GFS are. Therefore POPs are only in the 40 to 50 percent range.
Lows tonight are not expected to fall very much due to southeasterly
winds continuing to advect low level moisture into the area. This
moisture advection is expected to lead to a stratus deck expanding
across the region helping to keep lows generally in the lower 50s.
Think there could be some scattered showers and storms ongoing
Thursday morning. Am not sure how far east the precip could move as
the better forcing appears to be mainly across western and central
KS. But this activity should diminish by the late morning and early
afternoon as the vort max lifts north along with the forcing.
However models show another wave lifting towards the state late in
the day Thursday. As it does, instability is progged to increase to
around 2000 J/kg with not much inhibition. Deep layer shear remains
rather weak with values around 15 to 20 KTS. So think chances for
precip should be on the increase late in the afternoon. Isolated
storms may briefly be strong, but it is hard to see an organized
severe risk due to the weak shear. Models show the boundary layer
mixing out the low level moisture possibly leading to partly sunny
skies. With some insolation, think highs could reach the mid 70s as
925MB temps warm to around 19C. Have temps a little cooler across
north central KS where precip in the morning could help keep clouds
in place a little longer in the day.
.LONG TERM...(Thursday Night through Wednesday)
Issued at 347 PM CDT WED APR 15 2015
Thursday night could bring the most potential for severe weather
into the area, though it still looks rather low. Storms forming to
the south and west near and along the dryline in the late
afternoon could persist into the night as a moderate low level jet
develops and moisture continues to stream north into Kansas. At
this point would expect the boundary layer to stabilize before
storms could reach this far but elevated lapse rates could be high
enough to support some large hail. With the better forcing and
moisture to the west, have trended higher pops to this area.
Models becoming increasingly agreeable on the upper low`s timing
east east through Kansas in the Friday night to Sunday period. Would
anticipate the better large scale lift with this to be in the Friday
night and Saturday periods and have highest overall pops here,
though still not categorical. Could see drier air make its way into
central Kansas by late Saturday morning for a drying trend there.
Other details remain to be worked out including timing of waves of
precip and how much destabilization can take place between them if
they occur peak heating, with lapse rates aloft continuing to
weaken. Deep shear could be enough to support some stronger storms
if all elements come together.
Saturday night thru Sunday looks to be the best chance of spotty
rain and thunderstorm chances during the extended period. The upper
level cut-off low is expected to move and fill more rapidly to the
East/northeast as the main polar front trough amplifies and merges
with this system as they move into the middle and upper Mississippi
Valley together. There could be enough isentropic lift and
destabilization in the form of a cold pool aloft and just enough
MUCAPE to cause brief thunder. However, most areas will likely
stabilize into the evening as not much Sun during the day is
expected to aid with any destabilization. There may be another
brief window for showers and thunderstorms into the day early Sunday
and early afternoon, before the cold front finally moves through the
area providing weak CAA.
Monday thru Wednesday are expected to be generally dry before we
see a trough dig into the Great Basin and Central Rockies region
by Wednesday bringing small chances for rain on Wednesday mostly
later in the day as a weak shortwave may be ejected out ahead of
the main trough.
High temperatures throughout the period look to remain in the 60s
with the weak CAA and possibly some areas seeing patchy areas of
frost into the morning Tuesday.
.AVIATION...(For the 18Z TAFs through 18Z Thursday Afternoon)
Issued at 1212 PM CDT WED APR 15 2015
Am pretty confidence that CIGS will remain above 2 KFT this
afternoon. However they could bounce around 3 KFT for some time.
Satellite starting to show clouds thinning with the boundary layer
deepening per MHK latest OB. Think this is likely at TOP and FOE,
so have a VFR forecast prevailing this afternoon. Low level
moisture advection persists through the night. Because of this
think there is a reasonable chance for MVFR stratus to return.
However I don`t have enough confidence in the MOS prog of IFR
conditions to include in the forecast at this time. There may be
some elevated showers and thunderstorms Thu morning, but the
better forcing may end of staying west of MHK and the probs
appear to low to mention in the forecast.