Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 281205
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
605 AM CST Wed Jan 28 2015
.SHORT TERM: (Through Late This Afternoon)
Issued at 339 AM CST Wed Jan 28 2015
Satellite data at 08z showed the area of low clouds that had been
across west-central IL had moved off to the north, propelled by low
level flow from the SE, leaving behind clear skies across the entire
forecast area. Temps were in the 20s for most areas save central MO
where readings were in the low 30s. A surface warm front extended
from southern NE to northeastern OK. NW flow prevailed aloft with
an upper level RIDGE over the Plains.
The surface warm front is expected to make steady progress today
into central MO by late afternoon. While moisture levels in the
atmospheric column are expected to rise to above average levels, the
lack of any real deep lift other than from the front will preclude
any pcpn development thru early this evening. In fact, clouds are
expected to be rather thin for much of the day until late, allowing
plenty of sunshine.
The high levels of sunshine and what should be a stout southerly
surface flow will allow temps to surge today, especially in central
MO where the surface warm front is expected to reach. MOS temps
have been consistently on the cool side for similar scenarios this
year. Forecasted values that were around the warmer MAV MOS for IL,
yielding 45-50F for maxes, and went up to a few degrees above the
MAV MOS for MO, yielding low 50s near the MS river to the low 60s in
.LONG TERM: (Tonight through Tuesday)
Issued at 339 AM CST Wed Jan 28 2015
(Tonight through Friday)
With little precip expected thru the period, focus remains on temps.
Mdls are in very good agreement thru the period with respect to mass
fields and thermal profiles. Still, spread among MOS temps increases
thru the period, tho is less than usual. Have trended twd the warmer
guidance for tonight as clouds shud help keep temps warmer. Trended
twd a compromise thru the remainder of the period as cloud cover and
CAA will oppose one another, increasing uncertainty.
Continued low PoPs for nern/ern portions of the CWA for tonight and
Thurs morning as the clipper pushes thru the area.
(Saturday through Tuesday)
Focus quickly turns to the system approaching the region this
weekend. Mdls are in remarkably good agreement thru the end of the
storm on Mon. Overall, mdls are rather consistent compared to 24 hrs
ago. However, the ECMWF is slightly less amplified and slightly
warmer while the GFS suggests a deeper trof and overall cooler. The
GEM is further nwd with the 850 mb track compared to the other
Increased PoPs for late Sat thru Sun as mdls continue to suggest
precip thru this time and precip is expected. However, a fair amount
of uncertainty remains regarding p-type thru this storm. Still, it
shud remain largely a RA vs. SN system. With the uncertainty in the
thermal profile, only minor changes were made to p-types for this
system. This storm will remain one to monitor.
Beyond this storm, much colder air filters into the region as the
arctic sfc ridge builds into the area. Have trended slightly cooler.
Any SN pack from the preceding system may drive temps even cooler
than forecast. Will continue with an overall compromise for now.
.AVIATION: (For the 12z TAFs through 12z Thursday Morning)
Issued at 605 AM CST Wed Jan 28 2015
VFR conditions and dry wx will prevail today with S-SE surface
winds strengthening and becoming gusty. A 50kt low level jet will
develop this evening and result in LLWS conditions at all TAF
sites. Increasing clouds and lowering CIGs will be featured for
late tonight. Surface winds will veer SW and become gusty again,
ending the LLWS, with a cold front for close to the end of the
valid period, veering winds from the NW and increasing gusts to
25-30kts. MVFR CIGs are also expected to overspread the area
behind the cold front. No pcpn is anticipated but could see some
spotty light rain mainly E of the MS river.
Specifics for KSTL: VFR conditions until late tonight. S-SE
surface winds will become gusty today, with LLWS developing this
evening in conjunction with a 50kt low level jet. LLWS conditions
are expected to come to an end with what should be veering and
gusty SW winds late tonight with further strengthening around 12z
with a cold front moving thru. MVFR CIGs will then also move in
with the cold front.