Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 030434
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1134 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 06z TAFs through 06z Wednesday Night)
Issued at 1119 PM CDT Tue Sep 2 2014
The main fcst concern for this pkg is the fog threat overnight.
VSBYs have dropped to IFR at several stations across the area,
just not at any of the the TAF sites...yet. A moist bndry layer
coupled with good radiational cooling should lead to widespread
fog dvlpmnt overnight. KSUS and KCPS will likely have the densest
fog due to their river valley locations with other terminals
optimistically remaining MVFR. Did not include VSBY restrictions
at KUIN due to lack of rainfall last night. Trends will have to
monitored overnight for updates. Convection has already initiated
across KS this evng. This activity will work ENE overnight and
should stay north of KCOU and will dsspt before making it as far
east as KUIN. A weak SFC bndry will lift north thru the area
tomorrow aftn and is fcst to initiate TSTM dvlpmnt. Due to low
confidence on the coverage of the convection...did not include
mention in the TAFs.
Specifics for KSTL:
Light winds and clear skies overnight will allow for at least
MVFR fog to dvlp towards sunrise. An update may be needed if the
fog forms sooner or is more dense than anticipated. The fog
should burn off by mid mrng with diurnal cu forming shortly
thereafter. There is the chance for some aftn convection...but
questions about the coverage precludes mention in the fcst attm.