Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 200410
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1110 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 06z TAFs through 06z Wednesday Night)
Issued at 1110 PM CDT Tue Aug 19 2014
A weak cold front was draped from central IL thru northern MO late
this evening and was producing very little in the way of clouds
and only one cell just to the east of UIN. This front is expected
to move thru our region uneventfully for the next few hours 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 upgraded to
VCTS mention, but southern extent looking a bit more iffy if front
does not work its way far enough south as originally expected. 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.