Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 022055
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
355 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
most locations.

TES

.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
the area.

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.

TES

&&

.AVIATION:  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1226 PM CDT Tue Sep 2 2014

Celings across the area have been slow to improve today, and while
KUIN has gone VFR, MVFR ceilings are still affecting KCOU, KSUS,
KSTL, and KCPS. Expect improvement early this afternoon within an
hour or two of TAF valid time, with ceilings becoming scattered
VFR and then clearing after sunset this evening. With clear skies
expected overnight, attention then turns to potential fog
development. Currently, it looks like metro TAF sites as well as
KCOU have a better chance to see fog, given extra available
boundary layer moisture due to recent rainfall. Have introduced a
few hours of MVFR fog for the aforementioned locations for the
late overnight/early morning time frame, and a brief window of IFR
for KSUS. Otherwise, northwesterly winds today will become light
and variable overnight, and then become southerly on Wednesday as a
front lifts northward through the area. Showers/thunderstorms are
possible area-wide on Wednesday afternoon as well, though
uncertainties in timing/coverage preclude mention in the current
TAF.

Specifics for KSTL:

MVFR ceilings are expected to improve to scattered VFR within an
hour or two of the valid TAF period this afternoon, and then clear
after sunset later this evening. Given clear skies and ample
boundary layer moisture, have included mention of MVFR fog for
several hours during the late overnight/early morning time frame.
While 12Z models indicate the potential for some IFR fog
development, mainly right around daybreak Wednesday, have not
mentioned in the TAF at this time, and will defer to later shifts
to make the call if model trends are maintained. Northwesterly
winds this afternoon are expected to become light and variable
overnight, and then become southerly on Wednesday, and while
showers and thunderstorms are possible on Wednesday afternoon,
uncertainties in timing/coverage preclude mention in the current
TAF.

JP

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX




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