Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 300544

1144 PM CST SUN NOV 29 2015

Issued at 905 PM CST Sun Nov 29 2015

Weather features across the region remain fairly nebulous this
evening, but it appears that weak and slowly increasing WAA
around 850mb is becoming the main driver of precip across the
region this evening. Although the increase in UVV with the WAA is
certainly subtle, in the moisture laden AMS it appears to be just
enough to lead to the development of several areas of light rain.

PoPs have been tweaked several times during the evening primarily
on radar trends, and this will likely be the case for the rest of
the evening and into the predawn hours given the fact that the
forcing is so weak it`s difficult to use model output to pin down
exact trends. Mass fields as well as hi-res precip output
certainly suggests that with time the main focus of the precip
should be over the northwest half of the CWA where the WAA remains
the most persistent; however, given the extent of the moisture I`m
not certain if threat will ever totally end in southeast parts of
the FA.

Temps will likely hold nearly steady in most areas.



.SHORT TERM:  (Through Late Tonight)
Issued at 255 PM CST Sun Nov 29 2015

The cloudy and rainy weather pattern will continue tonight as
southwest flow shortwaves continue to move through our area ahead of
the upper level low currently located over WY and UT.  The majority
of the rain should be on the light side with just drizzle at times.
The best chance of rain will likely occur in the evening with the
latest radar depicting plenty of light rain upstream of our forecast
area across western MO. Temperatures will be warm enough that the
precipitation will be all liquid rain with no freezing or frozen
precipitation expected. Lows tonight should be similar to the
previous night. Went just above MOS guidance due to the overcast
cloud cover.  The MOS temperature guidance has been a little too
cold on nighttime lows the past couple of days.


.LONG TERM:  (Monday through Next Sunday)
Issued at 255 PM CST Sun Nov 29 2015

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 the closed LOW system as it eventually
tracks to our north.  This will combine with what will initially be
an occluded front passing thru late in the day, with a cold front
shortly after.

Another rain event will thus result on Monday and perhaps into Monday
evening, with the best rainfall amounts 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

P-types will be entirely rain with vertical temp profiles strongly
supportive of liquid falling, and surface temps remaining above
freezing when any pcpn is falling.  Cold surfaces not a factor
with it being early in the season and lack, thus far, of any
significant recent cold air outbreaks.

With extensive cloud cover anticipated, favored daytime max temps
Monday at or slightly below the coldest MOS.

Models remain in good agreement from Tuesday thru early
Thursday, with a synoptically unfavorable position for pcpn on
Tuesday with a wound-up storm due north, and NW flow aloft
Wednesday and Thursday with surface high pressure dominating.  Temp
recovery on Tuesday looks intriguing, with the edge of a cooler
airmass trying to build in, but otherwise, a very favorable setup
for a nice warmup, with multiple sightings of the sun anticipated for
the first time in days and deep mixing for late November with breezy
WSW winds.

Look for slightly below average temps Wednesday as the colder air has
a better chance to deepen and already a recovery to slightly above
average by Thursday.

There remains model disagreement later on Thursday on how to handle
the evolution of a shortwave in this NW upper flow but with moisture
expected to be at a premium by this time, its impacts are expected
to be minimal to nil.

Otherwise, building heights and ridging aloft then takes hold for
Friday and Saturday with what could be well above average temps
as southerly surface flow kicks in.  Current forecast reflects
max temps in the 50s, but could see some 60s from this setup.

Yet another cutoff system could impact our region for next Sunday,
but timing tends to favor the slower solutions here so went on the
low-end with PoPs for liquid pcpn, plus plenty of time to watch the



.AVIATION:  (For the 06z TAFs through 06z Monday Night)
Issued at 1133 PM CST Sun Nov 29 2015

Expect flight conditions to continue to deteriorate tonight along
and east of the Mississippi. Low level flow is already beginning
to become more easterly...cutting off the flow of drier air from
the north. Should see low MVFR and IFR with continuing areas of
light to occasionally moderate rain overspread the entire area by
mid to late morning. IFR conditions with rain will prevail through
the day and into the evening ahead of a cold front. Should see
rain end after the front passes, and ceilings will likely improve
a bit as drier air filters into the area...tho ceilings below 2000
FT still look likely.

Specifics for KSTL:

Should see ceilings drop over the next several hours as the low
level flow turns to the east and southeast. This will stop the
flow of drier air from the north which has kept ceilings above
1000 FT this evening. Expect ceiling to drop below 1000 FT between
08-10Z. Some guidance has ceilings getting quite low on
Monday...perhaps as low as 300-400 FT which would be at or below
alternate minimums. Not ready to forecast ceilings that low, but
wanted to mention that it is a possibility. Low ceilings and
periods of rain will continue on Monday. Should see the rain end
and some slight improvement in ceilings Monday night after a cold
front passes through the region.





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