Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 290334
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
934 PM CST SAT NOV 28 2015
Issued at 930 PM CST Sat Nov 28 2015
Somewhat nebulous precip threat over the CWA this evening as AMS
certainly remains saturated, but lifting mechanisms are weak and
rather ill-defined. There does appear to be two potential areas of
somewhat stronger ascent...the first is over southern sections of
the CWA, where several minor shortwaves appear to be embedded in
the strong westerlies. The second area is currently over nw MO,
where weak WAA into 850 baroclinic zone appears to be aiding
precip. In between, rain threat will likely be limited to some
drizzle or very light rain/sprinkles.
Just getting a look at some of the new 00z data, and it
would appear that the aforementioned WAA over nw MO will be
working into northern sections of our CWA by tomorrow morning.
Therefore, have allowed some low chance pops associated with this
lift to work into northern sections of the CWA after midnight
tonight, and have maintained this threat into the morning hours.
Temps in our far northwest counties would suggest a threat of
frozen precip during the predawn hours if the precip does reach
this area. Don`t think this would be a big deal given warm ground
temps and what should be a rather brief period of time temps will
be below 32, but will certainly continue to monitor.
.SHORT TERM: (Through Late Tonight)
Issued at 255 PM CST Sat Nov 28 2015
Although the cold front has pushed well south-southeast of
our forecast area, extending from southern AR northeast into
southern OH, will continue to get waves of mainly light rain moving
through at least parts of southeast MO and southwest IL tonight as
weak west-southwest flow shortwaves continue to move through the
region ahead of the upper level low over the Rockies. The models
were depicting upper level divergence over our region well ahead of
the upper level trough or low. There may also be some patchy
drizzle across our area tonight from the persistent low level
stratus cloud deck. Temperatures should be warm enough that the
precipitation will fall as liquid rain, although could not rule out
a little light freezing rain or drizzle across parts of northeast MO
late tonight. May be a little erosion of the low level cloud deck
across parts of northeast MO and west central IL due to drier air
advecting in from the north on the southern periphery of the surface
ridge moving eastward through the northern Plains. There should
still be mid-high level cloudiness across this area. With continued
cloud cover the model MOS low temperatures tonight look a little too
cool and went just above guidance for minimum temperatures for most
.LONG TERM: (Sunday through Next Saturday)
Issued at 255 PM CST Sat Nov 28 2015
(Sunday - Monday)
As the wound-up western CONUS storm begins to stir eastward, the
pattern over our region remains status quo thru Sunday night, with an
active southwest flow aloft and additional disturbances tracking
thru, overrunning moisture well to the north of the old surface
boundary at times in a light pcpn "flare-up".
One of these such "flare-ups" will be later in the day on Sunday and
into Sunday night. The models are showing the initial outbreak of
rain to be in central MO by early afternoon with it then expanding
mainly to the north from there but the atmosphere and synoptic setup
is such that it will be hard to go completely dry in other areas.
Bumped PoPs to likely for areas north and west of STL metro, with
low chances elsewhere. QPF looks to be light for areas that do get
pcpn, with up to one-quarter inch liquid equivalent possible.
The influence of the main storm system center itself will be felt on
Monday and Monday night as an upper level disturbance rotates around
the southern periphery of what should still be a closed LOW as it
tracks to our north. This will combine with what will initially be
an occluded front passing thru, with a cold front shortly after.
A more widespread rain event should result on Monday and perhaps
into Monday evening, but the best rainfall amounts will once again
be found over areas north and west of STL metro where the better
upper level support will reside. Up to a third of an inch of
liquid equivalent will be possible from this event.
P-types throughout this period should be entirely rain with vertical
temp profiles strongly supportive of liquid falling, and surface
temps should remain above freezing when any pcpn is falling. Too
early in the season to worry about cold surfaces influencing things.
With extensive cloud cover anticipated, favored daytime max temps at
or below the coldest MOS; conversely preferred nighttime min temps
at or above the warmest MOS.
(Tuesday - Next Saturday)
Models in better agreement throughout this period than they were
yesterday, with major items worked out. Wound-up storm begins the
period to the north and pulling away, with NW flow aloft thru
Thursday and an ill-defined and weak shortwave that passes thru a
moisture-starved column on Thursday, showing preference for the EC
solution from yesterday. Ridging aloft then takes hold for late
week. No signs of any significant cold air intrusions thru this
period, with seasonable to above average temps preferred by mid-late
This will all combine with westerly surface flow thru Thursday,
becoming southerly Friday and Saturday. With strong influence from
high pressure throughout, this will favor a dry forecast for a
One interesting item of note, depending on how fast the cooler air
builds in on Tuesday, could see temps reach the mid 50s in spots
thanks to anticipated deep mixing from WSW flow. After a brief
cooldown from there Wednesday and Thursday, could very well see
temps make a run on 60F by week`s end.
.AVIATION: (For the 00z TAFs through 00z Sunday Evening)
Issued at 532 PM CST Sat Nov 28 2015
Ceilings will stay on the edge of IFR along and south of the I-70
corridor tonight all night tonight. Should see some improvement in
ceilings further north across northeast Missouri and west central
Illinois as drier air filters south across the region. Further
south across the eastern Ozarks and into southern Illinois, I
expect little if any improvement over the IFR conditions currently
being reported. Latest guidance shows some improvement for most of
the area on Sunday ahead of the next wave of rain which will move
into central Missouri by early afternoon...but I don`t think
ceilings above 3000 FT are likely anywhere except across
northeast Missouri and west central Illinois.
Specifics for KSTL:
Ceilings took a little bump up last hour, so am going on the
premise that drier air filtering in from the north will keep
ceilings above 1000 FT for the rest of the night. That being said,
can`t rule out a drop back to IFR later this evening or overnight.
Ceilings should rise to between 2000-3000FT on Sunday afternoon
ahead of the next wave of rain which will affect the terminal late
Sunday night into Monday.