Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 030008
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
708 PM CDT Tue Sep 2 2014
.SHORT TERM: (Through Late Tonight)
Issued at 355 PM CDT Tue Sep 2 2014
A weak area of high pressure was centered over northeast KS and
attempting to push some drier air into our region currently.
Dewpoints have slipped into the lower 60s across northern MO but the
drier air has been less effective elsewhere where dewpoints remain
near 70. An expansive area of low stratus clouds existed this
morning but has since dissipated.
Clouds are expected to continue to exit or dissipate heading into
the evening hours and with the weak area of high pressure building
in and minimal continued dry air advection once the winds become
near calm, we are expecting fog to develop over the still wet to
nearly saturated ground for many locations in southwest IL and
extending back up the I-70 corridor into MO.
It still looks like nocturnal convection will get going with
development of the low level jet, but will be well west of our area
and will take much, if not all, of the night to get close to central
MO. Backed off on PoPs as a result thru 12z/Wed.
Favored the cooler MOS temps due to anticipated fog development at
.LONG TERM: (Wednesday through Next Tuesday)
Issued at 355 PM CDT Tue Sep 2 2014
What does develop tonight still looks on track to eventually advance
eastward into our region on Wednesday but will probably weaken and
redevelop to some extent with the heating of the day as it slowly
progresses thru. Backed off on timing a bit with most areas
probably seeing their best chances for rain on Wednesday afternoon
versus the morning.
Lessening chances for rain will then be seen heading into Wednesday
night, especially into MO, as the leftover convection from the
daytime limps into IL.
Thursday through Friday still on track to be well above average for
temps, with Thursday looking increasingly likely it will need a heat
headline and this may extend into Friday. Friday will depend on how
fast an approaching cold front, and its associated rain, work into
Best chances for rain rest of the week look to be what develops
along this late week front: Friday afternoon and night.
Behind the front, we are still looking at a nice period of below
average temps for Saturday thru Monday with dry wx. Temps will
rebound some with rain chances returning on Tuesday.
.AVIATION: (For the 00z TAFs through 00z Wednesday Evening)
Issued at 643 PM CDT Tue Sep 2 2014
SFC bndry now well to the south along the KS/OK and MO/AR border
and on into the OH valley. Skies should clear this evening with winds
become lght/vrb after sunset. SFC high pressure will drift overhead
tonight. With the rain from last night allowing for a moist bndry
layer...expect widespread fog to form after midnight due to favorable
radiational cooling conditions. VSBYs may be lower than currently
indicated...will have to monitor trends overnight. Left mention of
fog out of KUIN due to limited precip. Fog should dsspt tomorrow
mrng with diurnal cu forming. Guidance indicates that convection
should dvlp overnight across ern KS on the nose of the LLJ as it
intersects the SFC bndry. This activity is expected to slide east
into MO Wednesday morning, weakening as it does so. There is some
question as to how far east the precip will make it before dssptng.
The bndry is fcst to work back north tomorrow aftn...possibly
bringing another chance for SHRA/TSTM activity. The chance for
aftn convection partially depends on what happens with the earlier
precip and assoc cloud cover. Due to the uncertainty...opted to
leave out for now.
Specifics for KSTL:
Clearing skies this evng and light winds overnight will allow fog
to form after midnight. Unsure how dense it will become at the
terminal, so opted to leave it MVFR for now but, trends will need
to be monitored overnight. Fog should dsspt tomorrow mrng with
diurnal cu forming. There is a chance for either late mrng and/or
aftn SHRAs/TSTMs as a bndry lifts north thru the area. Due to low
confidence on coverage...decided not to include in the TAF attm.