Area Forecast Discussion
Issued by NWS Topeka, KS

Home | Current Version | Previous Version | Graphics & Text | 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

FXUS63 KTOP 231151

Area Forecast Discussion
National Weather Service Topeka KS
651 AM CDT Fri Mar 23 2018

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 248 AM CDT Fri Mar 23 2018

The forecast for the next 24 hours has several components of
uncertainty, both in terms of cloud/temp trends today and
thunderstorm chances tonight.

Early morning water vapor imagery showed a longwave trough off the
Pacific coast with an attendant shortwave ejecting ENE into the
Great Basin. At the surface, lee cyclogenesis was underway along the
Front Range with a broad surface trough/developing baroclinic zone
arching ENE into central Kansas. Mid to high level clouds were
streaming over the H500 ridge and into the Central Plains, with
lower-level stratus slowly forming across far eastern KS and into
MO. An expanding swath of lower stratus marked the leading edge of a
return moisture plume moving northward in northern Texas.

The lee cyclone pulls eastward by midday and tracks into western KS
by 00Z, crossing the KS/MO border by 12Z Sat. The broad warm front
looks to lift northward to near the KS/NE border as the low
approaches. The question for temperatures today hinges on how
quickly the Southern Plains stratus can reach the CWA. Current
extrapolation trends do not bring the stratus into the area until
mid-afternoon, as hinted at by the RAP/HRRR. As a result, there is a
15-20 degree spread in forecast highs today amongst the various
guidance solutions. Given the ongoing trends, have pushed highs
today closer to the high end of the temperature envelope. Some
locations in the SW CWA are forecast to hit 80 degrees as the warm
sector becomes more established ahead of the low and H850 temps
reach +15 C.

The next issue of the forecast revolves around the timing and
location of precipitation later today. Increasing theta-e advection
in the warm sector may lead to the generation of drizzle or showers,
but confidence in this precip is quite low given the uncertainty in
how soon the return moisture arrives. As the upper wave approaches
and isentropic upglide increases, elevated showers and thunderstorms
are forecast to develop along and north of the warm front tonight.
Convection will need to overcome a +12 to +15C cap in NE Kansas and
despite modest height falls near the border, there remains a large
degree of uncertainty as to if the forcing will be strong enough to
cool the profile. Should storms manage to fire, steep lapse rates
and 30-40 kts of effective shear would be enough to support stronger
cells capable of producing hail. One possibility is that convection
fires further west where the inhibition is less (though still
appreciable) and then rolls east along the KS/NE border.

The low pulls eastward and drags a weak cold front along its
southern flank late in the night. Have increased POPs with the
passage of this boundary early in the morning before the system as a
whole departs by sunrise.

.LONG TERM...(Saturday through Thursday)
Issued at 248 AM CDT Fri Mar 23 2018

On Saturday the departing midlevel shortwave trough continues
eastward over the mid MS valley allowing cooler and drier
continental air to filter into the forecast area. The diurnal
temperature swing will be minimized by this advection and a
possible stratus deck. Highs will range from the upper 40s is far
northeast KS to the upper 50s in central and southeast KS.
Residual low-level saturation should keep the stratus reinforced
into Sunday so highs remain in the 50s. A longwave trough begins
to deepen over the western US supporting the return of 850
moisture. The NAM and ECMWF are quite aggressive with this
moisture advection and widespread isentropic lift during the day
Sunday. Despite this moisture the MUCAPE will be limited due to
marginal midlevel lapse rates. As a result the chances for rain
increase into the afternoon with perhaps some embedded thunder.
The isentropic lift continues Sunday night as a plume of steep
lapse rates spreads over the plains in association with the
western trough. Thunderstorm coverage should increase during the
overnight with the elevated cape possibly reaching 1000 J/kg. In
fact a majority of the GEFS members show a modest increase in
MUCAPE between 06-12z Monday. Given the instability and shear
elevated storms capable of producing large hail can not be ruled

By Monday morning the longwave trough tracks over the eastern
Rockies with several embedded shortwave troughs. At the surface a
warm front will try lo lift through eastern KS while a low pressure
and dry line moves toward central KS. It appears a shortwave will
track over the Northern Plains which will force a cold front
southward that will eventually take over the dry line. It is still
uncertain how much of the warm sector will cover the area. With
clouds and precipitation during the morning it is unknown how much
the warm sector can destabilize. If any instability can be realized
and storms form along one of these surface features then perhaps a
few could be strong. Given the deep layer shear is nearly parallel
to the surface boundary a linear convective mode would be
favored. The cold front sags southward through the area Monday
night. Therefore precipitation could linger into Tuesday morning.
The model guidance is beginning to agree that the heaviest axis of
rainfall will be around southeast KS and the MO Ozarks. The
forecast area should begin to dry out on Wednesday. As the
longwave trough lifts over the region on Thursday precipitation
could clips portions of southeast KS.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 645 AM CDT Fri Mar 23 2018

Marginal LLWS will continue through the mid-morning before mixing
out. Easterly winds will gradually veer to the S/SE this afternoon
and evening. An area of low pressure moves through between
midnight and 6am, causing winds to switch to the NW in its wake.
MVFR to IFR stratus is forecast to overspread the area this
afternoon and tonight, through confidence in the timing of the
stratus is on the lower side. Showers and thunderstorms are
possible, primarily along and north of I-70 tonight. LLWS may
return between 03-09Z Fri night/Sat morning, though confidence was
not high enough to mention in the TAFs.




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