Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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 KEAX 200908

408 AM CDT Sat Sep 20 2014

Issued at 408 AM CDT SAT SEP 20 2014

Water vapor imagery this morning shows a flat pattern in place
across the Nation with a broad, low amplitude, trough moving east
through the Northern and Central Plains. Resulting lee-side
troughing has helped develop and push a cold front from the Northern
Plains into central Nebraska. The troughs progress east today will
continue to push the front south, though with the troughs neutral
axis tilt and the Pacific origin of the surface airmass behind the
front, the push will be slow. This will leave eastern Kansas and
Missouri well in the warm sector ahead of the cold front through the
day. This should make for a warm --in the 80s-- and breezy Saturday
in late September.

Ongoing convection, occurring along and just ahead of the front in
eastern Nebraska through central Iowa, is progressing south early
this morning thanks to the cold pool the rain is putting down.
However, persistent south winds overnight from a tightening pressure
gradient should inhibit the cold pools southerly progress and by
extension the progress of the storms. Have trimmed POPs a little
this morning on our northern border as a result, though keeping
isolated POPs for the errant activity that might effect our northern
border this morning.

As the front settles slowly south today pre-frontal warm air
advection will provide decent MLCAPE, with values bubbling up into
the 3000 J/KG range by this afternoon. This is coincident with 0-3KM
shear values in the 20 to 30 knot range, though deeper layer shear
of 0-6KM is a bit more promising with 40 knots. So, any storms that
can get going will have some potential for sub-severe to marginally
severe weather, with the primary threats looking to stem from hail
and damaging winds. However, models continue to not be optimistic
about the overall potential for storms as the upper level dynamics of
the trough and associated jet structure remain a bit farther north,
and surface convergence in the pre-frontal trough, or along the
front, are weak at best. This leaves the best kinematics somewhat
disconnected from the best thermodynamics. This doesn`t preclude
storms today, it just makes them a little harder to get going and
organize. Think the potential for some strong to marginally severe
storms will be there, especially this afternoon during peak heating;
but overall the lack of forcing will likely limit coverage. Still,
enough confidence is there now to warrant bumping POPs a touch in the
late afternoon to early evening hours into the likely range;
generally along and south of the Missouri River. Recent hi-res models
this morning back up this idea by advertising a scenario where
convection pushing south ahead of the front fades this morning, but
the out flow boundary progresses south into Missouri providing a weak
boundary to focus on for storm development during the mid to late
afternoon hours. Otherwise, expect storms to settle south tonight as
the front pushes in and to the south.

Sunday on...temperatures will be a little cooler, though thanks to the
Pacific origin of the air behind the cold front, temperatures wont
take to much of a dive over the next 7 days. Continue to expect
readings in the 70s for much of the next work week. Though, this
will come with another round of on-again-off-again rain chances as a
cutoff circulation --currently spinning off the coast of
California-- moves into the Plains only to bump into a persistent
surface ridge that will be in place across the eastern CONUS.
Intermittent storms and cloud cover could lead to more cool days.


.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
Issued at CDT FRI SEP 19 2014

Confidence in IFR/LIFR categories is starting to dwindle a bit as the
boundary layer remains rather mixy with southerly winds persisting
around 7 to 10 kts. Expect these winds of around 5 to 10 kts to
persist through most of the night, which will mitigate fog potential.
Given how moist the air mass is and temperatures dropping through the
night, still think some light VSBY restriction is in order through
sunrise. Regarding the stratus, even less confidence in that
occurring, as model soundings and guidance indicate that low level
stratus will have a hard time forming, especially with mid level
clouds currently gliding through the area. Will keep the mention for
stratus in the forecast for now, but will need to monitor closely and
amend as necessary, should the stratus not form. VFR expected after
sunrise, however thunderstorms are possible along an advancing cold
front Saturday afternoon and evening. Coverage will be isolated to
scattered, so exact timing of heavy rain and gusty winds at the
terminals is unclear at this time. Gave a window of most likely
precipitation for each terminal using VCTS group.




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