Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 200235

935 PM CDT Tue Aug 19 2014

Issued at 856 PM CDT Tue Aug 19 2014

The convection has shifted east of the forecast area with little
if any clouds left this evening. Still expecting convection to
develop over eastern Nebraska and southwest IA late this evening
and overnight on nose of swly low lvel jet over the Plains and
drop southeastward along and north of a subtle cold front
extending nw to se from around MCI southeast through STL area to
southern IL. The latest 00z Wednesday run of the NAM only
generates light qpf across northeast MO late tonight, while the
HRRR model is much more robust developing convection into
northeast MO shortly after midnight then ramps it up southeast
towards the St. Louis metro area by early morning. Will also
likely have patchy fog across east central MO and southwest IL
late tonight due to light surface winds, high surface dew points,
and little cloud cover in this area until early morning.



.SHORT TERM:  (Through Late Tonight)
Issued at 309 PM CDT Tue Aug 19 2014

Morning and early afternoon convection associated with a mid/upper
level shortwave has moved east of the CWA. Cold front approaching
from the northwest is sparking a few thunderstorms across extreme
northeast Missouri. Will watch this convection over the next hour
and decide how far south to forecast thunderstorms this evening
with the front.

Front is expected to settle into a northwest to southeast
orientation overnight from near Kansas City area to southern
Illinois. Model guidance is not as enthusiastic with convection
developing overnight - but with front in vicinity and low level
jet can`t rule out elevated convection. Have maintained chance
POPs for now and will let evening shift determine need to increase
or decrease by NOWCast.


.LONG TERM:  (Wednesday through Next Tuesday)
Issued at 309 PM CDT Tue Aug 19 2014

Story will be the HEAT and HUMIDITY. It`s finally going to feel
like summer with the first real heat wave beginning tomorrow. Have
decided to hoist an Excessive Heat Warning for the urban zones of
the Greater St. Louis Metropolitan Area. Temperatures will be in
the middle 90s tomorrow and rise into the upper 90s through at
least Sunday. The long duration of afternoon/early evening heat
index values around 105 degrees will cause life threatening
conditions for those that do not have access to air conditioning.

Outside of the urban areas, the heat will increase, but not reach
advisory levels until Friday. Will let later shifts access the
need for additional heat headlines.

There is still a chance, albiet slight, for thunderstorms to
develop on Wednesday as the warm front lifts through the area.
After that, I`m not sure we will see any rain until next week when
a front moves south and stalls somewhere across the Midwest. If
the front does not make it far enough south - the heat headlines
will likely have to be extended into the next work week.



.AVIATION:  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 655 PM CDT Tue Aug 19 2014

A weak cold front was draped from northwest IL thru northern MO
early this evening and was producing very little in the way of
clouds and no rain. This front is expected to move thru our region
uneventfully this evening and early overnight, before stalling out
and eventually retreating to the north as a warm front late. When
this does happen, scattered convection is expected to break out
along the front as it pushes thru the TAF sites thru mid Wednesday
morning. Have added VCSH for now for timing purposes but there
will also be a threat for thunder as well, but can escalate later
this evening. Some fog is also expected, especially at SUS and
CPS, but will be in a narrower window than last night due to the
expected clouds and convection firing along the warm front. VFR
conditions are then expected for the remainder of the TAF period
from late Wednesday morning on as the entire area moves into a
warm sector setup. Surface winds will become S-SW as the warm
front moves thru.

Specifics for KSTL: VFR conditions outside of rain are expected
thru the period. A small window early Wednesday morning for rain
is anticipated as a warm front moves thru. An outside chance for
some VSBY reductions in mist late tonight as well, but small
enough to preclude mention in the TAF at this time.



MO...EXCESSIVE HEAT WARNING from 1 PM Wednesday to 7 PM CDT Sunday
     FOR St. Louis City MO-St. Louis MO.

IL...EXCESSIVE HEAT WARNING from 1 PM Wednesday to 7 PM CDT Sunday
     FOR Madison IL-St. Clair IL.



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