Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 030105

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
705 PM CST Fri Dec 2 2016

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 323 PM CST Fri Dec 2 2016

Two areas of clouds will affect the CWA tonight into tomorrow.
Lingering clouds to the NE continue to slowly move south through the
overnight but will gradually lift north tomorrow afternoon as system
to the SE moves into the area. Light northwesterly winds through
tomorrow morning shifting to easterly by tomorrow evening. High
clouds move into the SW CWA ahead of the next system tonight and
continue to the NE.

The timing of the cloud movements make temps a bit tricky. Light
northwest wind and possible clearing could lead to good radiational
cooling but introduction of high clouds (depending on their
thickness) could keep it in check. Went with a blend of both
scenarios for temps. Also, a few models show precip moving into the
western/southern counties of the CWA tomorrow afternoon but
soundings show that there will be dry low to mid levels. With that
in mind went with dry forecast as it will take some time to saturate
to the surface.


.LONG TERM...  (Saturday Night through Next Friday)
Issued at 323 PM CST Fri Dec 2 2016

Rain will spread northeastward through our forecast area Saturday
night well north of a surface low centered over the southern Plains
and ahead of an approaching shortwave.  Models were depicting good
upper level divergence over our area ahead of the approaching upper
level trough moving eastward through the northern Plains and in the
right entrance region of an upper level jet streak over the Great
Lakes and Ohio Valley regions.  The highest QPF late Saturday night
and Sunday morning should be across northeast MO and west central IL
associated with the shortwave/vorticity maximum.  Although the
forecast soundings indicate mainly rain with a relatively high
freezing level, would not be surprised to see a brief period of
light snow across northeast MO and west central IL with a dusting of
snow accumulation possible on grassy areas.  Accumulation is not
expected on roads with warm road/surface temperatures.  A break in
the precipitation is expected Sunday night and Monday morning, then
rain will spread back into much of the forecast area Monday
afternoon and night ahead of a southern stream upper level trough
and associated surface low which will move northeastward through AR
and the Tennessee Valley region.  The majority of the QPF will be
across southeast MO and southwest IL in the northwestern periphery
of the surface low and will be in the form of liquid rain.  The rain
should shift east of the forecast area by Tuesday afternoon with
colder air filtering southeastward into the region as a large and
broad northern stream upper level trough moves eastward through the
northern Plains and a strong surface ridge builds southeastward into
our area from the northern Plains.  The GFS model does not have any
measurable precipitation for the rest of the extended forecast, but
the latest ECMWF model does bring a band of precipitation through
our forecast area Wednesday afternoon and night assoicated with a
shortwave and a secondary reinforcing cold front.  This
precipitation may start as rain, but would change over to snow
before ending with light snow accumulation possible.  Not real
confident with the ECMWF model solution and any accumulating snow
for our area, but am confident that the coldest air of the season so
far will impact our region beginning Wednesday night and continuing
for the remainder of the extended forecast.



.AVIATION...  (For the 00z TAFs through 00z Saturday Evening)
Issued at 705 PM CST Fri Dec 2 2016

Area of low-VFR CIGs has persisted across areas to the N and E of
STL metro since last night and show no signs of moving anytime
soon. If anything, as cloud level winds continue to veer light
from the N and NE, these clouds may slowly try to sneak into STL
metro later tonight. Something to watch closely, but fortunately,
CIGs are only around 3000-3500ft. Otherwise, VFR conditions and
light surface winds will prevail thru the valid period at the TAF
sites. Some pcpn may try to move in very late or just beyond the
TAF period, but probs not high enough to warrant mention at this





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