Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 012352
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
552 PM CST TUE DEC 1 2015
.SHORT TERM: (Through Late Tonight)
Issued at 255 PM CST Tue Dec 1 2015
Very little change to the previous forecast other than to expand
flurries mention thru early Wednesday morning into the I-70
corridor, and extend in time Wednesday afternoon for the IL counties
to account for a second strong vorticity lobe swinging thru.
A cold front will move thru tonight and will initially bring with it
increasing clouds from the northwest, including a field of low
clouds late. Of more interest is in addition there will be a strong
upper level disturbance rotating around the southern periphery of
the still wound-up storm system to our north that will track thru
much of our northern and central CWA later tonight and early
Wednesday morning. Current radar imagery already shows plenty of
radar echo associated with this feature. While the column will be
rather dry overall, the forcing/upper level support provided by this
feature along with cyclonic flow at the low levels and the likely
presence of a field of low clouds should at least provide the setup
for a seeder-feeder and the threat for falling pcpn from this. Dry
air remains an issue that will probably limit or prevent anything
measurable for most areas although isolated pockets of measurable
could still happen where everything lines up just right and will
almost need to be nowcasted later tonight when its evolution can be
better handled. Models continue to show the first strong vort lobe
rotating further south than 24hrs ago and have expanded the pcpn
mention southward as a result...into the I-70 corridor. Pcpn-types
later this evening, overnight, and Wednesday morning should be
predominantly snow. Boundary layer temps should warm sufficiently
Wednesday afternoon to have the second round of pcpn for IL mix with
and/or change to liquid sprinkles.
Leaned toward the higher MOS temps for nighttime mins tonight, and
lower MOS temps for daytime maxes on Wednesday for most locales.
.LONG TERM: (Wednesday through Next Tuesday)
Issued at 255 PM CST Tue Dec 1 2015
An extended period of above average temps during this period
still looks likely, with above average h500 heights aloft and
predominantly southerly flow at the surface. The warmest day
continues to look to be Saturday, where if the flow were more
southwesterly, would be more aggressive with the warmup into the
low 60s. But with a slight easterly component to the wind that
day, kept the forecast in the mid-upper 50s instead.
The only two items of interest this period are handling of a ridge-
runner shortwave that will zip into the central CONUS by Thursday,
but with a maintenance of a dry column, and the better forcing now
expected to remain south and west from this system, kept a dry
forecast for our area.
The other item is the strong Pacific storm system that now looks to
be better attached to the main flow than it was depicted 24hrs ago.
This could result in a faster onset, briefer impact, and less
ability to tap into Gulf of Mexico moisture in an otherwise still
dry column. PoPs have been reduced to slight and low chance
categories but continue to be advertised for Monday at this time.
Sure there will be further adjustments with this system, but temps
will be too warm for anything but liquid with this.
.AVIATION: (For the 00z TAFs through 00z Wednesday Evening)
Issued at 532 PM CST Tue Dec 1 2015
Large area of clouds across northern and western Missouri will
move southeastward tonight into the terminals. While still expect
the ceilings to be VFR at KUIN and KCOU, they should eventually
fall into high MVFR range overnight into Wednesday. Farther
southeast, the ceilings at the St. Louis metro TAF sites will
either be low VFR or high MVFR overnight through tomorrow
afternoon before clearing begins. Light south to southwest winds
will veer westerly tonight and become gusty on Wednesday.
Specifics for KSTL:
Low VFR or high MVFR ceilings will move into the terminal
overnight and remain through most of the day tomorrow before
clearing out during the afternoon. Current light southerly wind
will veer westerly tonight and become gusty on Wednesday morning.