Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 130826

Area Forecast Discussion
National Weather Service Saint Louis MO
326 AM CDT Fri Oct 13 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 324 AM CDT Fri Oct 13 2017

With surface ridge to our east, will see southerly winds return to
the region. This will allow temperatures to warm up well above
normal once again. Highs today will be in the upper 70s to mid 80s.

In the meantime, will see patchy fog persist, mainly along and east
of Mississippi River through mid morning. There could be areas of
denser fog, so will keep eye out for updates as needed.

By tonight, will see increasing mid and high clouds ahead of next
weather system. Models have been progressively slower with onset of
precipitation. For now have low chance pops for portions of
northeast MO/west central IL, mainly after 03z Saturday. A mild
night is in store with lows in the upper 50s to upper 60s.


.LONG TERM...  (Saturday through Thursday)
Issued at 325 AM CDT Fri Oct 13 2017

An upper TROF over the western CONUS early Saturday morning will
track thru our region on Sunday, give us a couple days of a dry
northwest flow aloft, with the pattern from Wednesday onward
uncertain with large model differences existing.

Not much sensible weather is anticipated for this stretch, with
the key feature being a surface cold front that will be the main
driver--with it set to begin upstream of our region on Saturday, and
then pushing thru on Saturday night.

Convection loosely in association of the front and approaching
weather system may already be ongoing in our area at 12z/Sat, with a
low level jet nosing in and some models kicking off early morning
convection, but due to the location of the jet, this early morning
convection should stay north of I-70 and is expected to dissipate
during the morning hours with the main focus then shifting north
towards the surface cold front.  The persistence of clouds and rain
chances throughout Saturday in northeast MO and west-central IL will
likely limit warming that is so precarious this time of year
considering the increasingly weakening sun angle.  Areas further
south towards the I-70 corridor and southward should be rain-free
enough (or entirely) during the day with much better insolation to
allow for a good setup for what should be unseasonably warm
temperatures that will inundate much of this area.  Previous
forecast appears to have a good handle on what should be needed
adjustments above the highest MOS temp forecast.  This forecast will
be in the neighborhood of record values, with STL looking the most
likely to fall.  See the CLIMATE section for more detail.

Showers and thunderstorms will get going in earnest by late Saturday
afternoon closer to what will still be an upwind cold front and this
will plow thru our region during Saturday night along with the cold
front itself.  Enough instability will persist into the evening
hours along with ample shear to support strong-severe storm
potential, but with the main threat being damaging straight-line
winds with large hail a lesser threat early in the episode.
Instability really tails off by midnight with pcpn now expected to
exit our region by early Sunday morning.  Looks to be quite a bit
of wind behind the cold front Saturday night into Sunday, with gusts
as high as 35mph.

Another very sharp contrast on temps by Sunday, with a drop off
approaching 30 degrees between maxes on Saturday versus Sunday!  A
gradual return of temps to above average expected by Tuesday with
southerly surface flow.  While the upper pattern looks uncertain
from Wednesday on, establishment of this southerly flow by Tuesday
will be hard to dislodge without a clearer signal for a TROF or
northwest flow aloft and could see another extended period of above
average temps.  Pcpn chances look minimal for much of next week.



.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1129 PM CDT Thu Oct 12 2017

VFR conditions for all termials to start the forecast period. Low
clouds have moved out leaving clear skies with a few mid level
clouds near UIN. Period will remain dry and winds will stay from
the south. Fog/low stratus is still expected for STL, SUS and CPS
beginning around 9Z.


VFR conditions to start the period but fog/low stratus is
expected to form after 9Z. IFR conditions will accompany the low
clouds/fog but should be VFR by 15Z. Period will be dry with light
winds from the south/southeast.



Record max temperatures for Saturday, 14 October...

Saint Louis:  90/1899
Columbia:     92/1899
Quincy:       91/1938




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