Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 240830
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
330 AM CDT Tue Oct 24 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 325 AM CDT Tue Oct 24 2017

A cold front has moved east of Missouri and Illinois early this
morning with westerly winds.  Isolated showers were found over parts
of Illinois associated with a weak shortwave trough rotating around
the upper low over northern Illinois.  Another trough currently over
the upper Midwest will rotate south across the area later today.
This will bring additional showers to the area later this morning
and this afternoon.  The greatest chance will be closer to the upper
low, so will keep the highest chance for showers over Illinois and
eastern Missouri.  The showers will exit south central Illinois and
southeast Missouri by late this afternoon as the trough rotates
around the trough.

Latest satellite imagery is showing cloudy skies over all but
southeast Missouri and far southwest Illinois.  This will continue
to be the trend through late afternoon before skies begin to clear
from the west when the trough moves off to the east.  The
combination of the clouds and rain will keep temperatures from
rising too much today with highs well below normal.  Skies will
clear during the evening hours as the upper low moves off to the
east and lows tonight will fall into the mid 30s.  Kept with just a
mention of patchy frost tonight because it still looks like winds
will be in the 5-10 mph range, and high clouds will move back into
the area late tonight. Without these factors, frost could be more
widespread.


Britt

.LONG TERM...  (Wednesday through Monday)
Issued at 325 AM CDT Tue Oct 24 2017

A quick rebound in temperatures is expected on Wednesday as strong
midlevel height rises and 850-hPa warm air advection begin in
earnest. A potent shortwave trough will dive southward across the
western Great Lakes into the Ohio Valley by Wednesday evening. At
the surface, a weak trough axis will move through the bi-state
region Wednesday afternoon so expecting a favorable WSW wind
direction promoting downslope off of the eastern Ozarks.
Consequently, leaned toward warmer MAV MOS numbers across portions
of central, east-central and southeastern Missouri. Look for
highs to range from the low to mid 60s across much of the area.

Another chilly night is likely on Wednesday night due to expected
clear sky, low dewpoints, and light winds promoting favorable
conditions for radiational cooling. Lows should be in the upper 30s
to low 40s, so not thinking there will be much if any in the way of
frost. However, cannot totally rule out some patchy frost across
favored valleys in southeastern Missouri which oftentimes tend to
cool off a bit more than forecast.

Warmest day of the extended portion of the forecast continues to
look like Thursday ahead of a strong cold front. Midlevel ridge
axis moves across the mid-Mississippi Valley during the day along
with 850-hPa temperatures rising into the mid teens. Warmed highs
Thursday afternoon a few degrees across the area from previous
forecast with upper 60s to mid 70s now expected. Cold front is
expected to pass through the CWA by late Thursday night. Expecting
a dry frontal passage, but amplifying midlevel trough and fairly
impressive upper-level jet dynamics will likely lead to an area of
rain across portions of southeastern Missouri and southwest
Illinois Friday afternoon and evening. Precipitation type looks to
be all rain as the boundary layer remains a bit too warm. If
precipitation lingers long enough into Friday night, the rain may
be able to briefly mix in with a couple of snowflakes.

Coldest air of the season remains on track for this upcoming
weekend. While a widespread freeze is likely for the entire area
between Saturday morning and Monday morning, there is still a
fair degree of uncertainty on specifics with respect to exactly
how cold it will get each night. Latest model trends are pointing
to warmer temperatures on Friday night/Saturday morning due to
lingering cloud cover with Saturday night (and even Sunday night)
potentially being the colder nights. Did not make too many
substantial changes but did trend a bit warmer for Friday night
and a bit colder on Sunday night as it looks like surface ridge
axis will be draped across the area.

Another quick moderation in temperatures is expected by Monday ahead
of yet another cold front as another shortwave trough transverses
the Upper Midwest. Expecting highs on Monday to get back into the
50s to near 60 degrees after only being in the 40s for the most
part Friday through Sunday.


Gosselin


&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1057 PM CDT Mon Oct 23 2017

A strong ridge of high pressure continues to build southeastward
into our area behind a cold front. Strong and gusty northwest
winds will continue late tonight and Tuesday due to a tight
surface pressure gradient between a deep surface low over the
Great Lakes region and a strong surface ridge building into our
area from the northern Plains. There will also be strong winds
aloft leading to some LLWS late tonight, but it appears that there
will be enough nocturnal mixing which will keep surface winds
strong enough and not warrant including LLWS in the tafs. Low-mid
level, VFR cloudiness will advect southeastward through our area
late tonight. Isolated showers may continue to move southeastward
through our area as well. Diurnal, cold air advection
stratocumulus clouds can be expected late Tuesday morning and
afternoon. These could be around 3000 feet when they develop in
the late morning and early afternoon. It appears that most of the
rain will be northeast of the taf sites on Tuesday on the backside
of the surface low over the Great Lakes region. The surface wind
will gradually diminish Tuesday evening.

SPECIFICS FOR KSTL: A strong ridge of high pressure continues to
build southeastward into our area behind a cold front. Strong and
gusty northwest winds will continue late tonight and Tuesday due
to a tight surface pressure gradient between a deep surface low
over the Great Lakes region and a strong surface ridge building
into our area from the northern Plains. There will also be strong
winds aloft leading to some LLWS late tonight, but it appears that
there will be enough nocturnal mixing which will keep surface
winds strong enough and not warrant including LLWS in the STL taf.
Low-mid level, VFR cloudiness will advect southeastward through
our area late tonight. Isolated showers may continue to move
southeastward through our area as well. Diurnal, cold air
advection stratocumulus clouds can be expected late Tuesday
morning and afternoon. These could be around 3000 feet when they
develop in the late morning and early afternoon. It appears that
most of the rain will be northeast of the STL area on Tuesday on
the backside of the surface low over the Great Lakes region. The
surface wind will gradually diminish Tuesday evening.

GKS

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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