Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 010010

710 PM CDT Tue Sep 30 2014

.SHORT TERM:  (Through Late Tonight)
Issued at 300 PM CDT Tue Sep 30 2014

Cu field on vis satellite marking the front quite well and currently
extends from through southwest Iowa to just north of St. Louis
into southern IL. The front may sag a tad south over eastern MO
into IL tonight as the surface winds back to more east-southeasterly,
but the portion of the front in our area is largely expected to
remain unactive. Further west/northwest however the LLJ shifts
eastward from the Plains overnight and becomes focused in the
vicinity of the front across northwest MO into southwest Iowa
favoring the highest shower/thunderstorm potential. Lows once
again tonight coolest from the eastern Ozarks through southern IL.
May once again see some patchy radiational fog as well.


.LONG TERM:  (Wednesday through Next Tuesday)
Issued at 300 PM CDT Tue Sep 30 2014

Active weather unfolds Wednesday and especially in the Wednesday
night into Thursday evening time. Multicellular convection is
expected to evolve on Wednesday afternoon across northwest MO and
progress into central and northeast MO during the late afternoon.
High temperatures will remain above average.

Thunderstorms are expected to really get going on Wednesday
night. At least one disturbance in the southwest flow aloft will
traverse northern MO Wednesday night, and this combined with a
veering and strengthening southwesterly LLJ will provide favorable
convergence/lift for convection across northern MO into west
central IL - especially along and north of a Jefferson City to
Litchfield line. Repetitive convection and some locally heavy rain
is certainly within the realm in this region. Thunderstorms remain
likely Thursday and Thursday night with the potential for some
strong-severe storms. This potential will probably be intimately
controlled by mesoscale features. Showers and thunderstorms are
expected to be ongoing Thursday morning across northern MO into
central IL with a convective outflow boundary likely to their
south. This boundary along with a pre-frontal convergence zone
will dictate to some degree the best instability and low-level
shear. Otherwise the advancing cold front and attendant short wave
trof will provide deep large scale ascent, and deep layer shear is
favorable for organized severe during the afternoon and evening
with the orientation suggestive of a linear mode. The vast
majority of showers and thunderstorms should be located well into
Illinois by 06z Friday and east of the CWA by daybreak Friday.

Friday is looking more and more like a typically blustery fall day
with much cooler temperatures and gusty northwest winds. A deep
long wave trof, which has become progressively stronger in the
latest model runs, will dominate the eastern half of the nation
from the weekend into early next week. This will result in below
average temperatures for most of that period.



.AVIATION:  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 650 PM CDT Tue Sep 30 2014

The backdoor cold front that pushed into the area this morning
continues to slowly work SSW. It currently stretches from sthrn
IL NW thru ern into n cntrl MO and on into wrn IA. This bndry is
fcst to stall this evng and then begin lifting north overnight as
the assoc sfc low over the Dakotas lifts into sthrn Canada by
Wednesday. Therefore winds should be ESErly overnight bcmng SSErly
during the day tomorrow...staying aob 10kts. By Wednesday
aftn...a bndry extending south from the original low in Canada to
a new sfc low...that is fcst to form overnight across the cntrl
high plains...will approach cntrl MO Wednesday aftn. This should
be the focus for at least isld/scttrd convection for cntrl and NE
MO and possibly as far east as w cntrl IL. Not confident enough on
the coverage/timing to include attm. Precip coverage becomes
greater after the valid time of this fcst. Other than the clouds
assoc with the convection late in the prd...can expect diurnal cu
and some cirrus.

Specifics for KSTL:

VFR fcst with ESE wind bcmng SSE Wed mrng as a frontal bndry moves
north of the terminal. There is the potential for convection late in the
prd...after 00Z Thu...but late enough in the fcst and enough
uncertainty in timing/coverage not to include attm.





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