Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 150555

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1155 PM CST Thu Dec 14 2017

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 328 PM CST Thu Dec 14 2017

Overcast skies expected to persist through the rest of the afternoon
into the evening. A clipper will approach the area from the
northwest late tonight. A few flurries are possible as the system
moves southeast overnight into the early morning hours over parts of
northeast and north central Missouri and western Illinois.
Overnight lows are expected to be cooler than this morning`s
values due to CAA continuing over the region. Northwest winds will
veer to the southwest as the trough passes on Friday morning.
Temperatures will be warmer and than today with highs in the lower


.LONG TERM...  (Friday Night through Next Thursday)
Issued at 328 PM CST Thu Dec 14 2017

The pattern aloft will be quasi-zonal over the Midwest into the
medium range...bringing mild temperatures and the chance for some
precip to the region.  The longwave trof over the western CONUS is
forecast to gradually weaken through early next week, but several
strong vorticity maxima will dive into the base of the trof through
that period and eject northeast into the Great Plains.  The first
wave will impact our area on Sunday as weak low level cyclogenesis
forced by the wave turns the flow around to the south and southwest.
Guidance is printing out a widespread area of QPF greater than 0.1
inch over the Mid Mississippi the ECMWF is actually
quite bullish with as much as .25-
.45 inch. The precip on Sunday looks like it should be all liquid
with southwest flow bringing rising temperatures to the region.

Guidance has the next wave in line moving into the region Monday
night into Tuesday...however there appears to be little low level
cyclogenesis associated with the second wave.  Low level flow stays
relatively parallel to the baroclinic zone and the mid level forcing
lags behind the deepest moisture.  The GFS does kick out some light
QPF with this feature, but the ECMWF is almost totally dry with just
a few spits of QPF.  Don`t really see a strong signal to increase
PoPs in this time period given the weak forcing and low QPF.

GFS and ECMWF diverge toward the end of the forecast.  The general
upper pattern is similar, but the GFS is slower than the ECMWF. Both
have another longwave trof developing over the western CONUS, but
the EC pushes the trof further east forcing lee side cyclogenesis
over Colorado and western Kansas Wednesday night.  The resulting
strong low moves northeast into the Midwest on Thursday and pushes a
strong cold front into Missouri during the afternoon.  The slower
GFS is less dynamic with a much weaker low drifting into the region
on Friday, but the airmass in the cold sector of the low is still
quite a bit colder in both models.  Either way, the temperatures
should be trending downward toward the end of next week.



.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1130 PM CST Thu Dec 14 2017

VFR conditions throughout the TAF period for all sites. All sites
will remain dry for the period with the exception of UIN. Slight
chance for light snow showers/flurries just before sunrise at
UIN. I think that the snow will occur but not a measurable amount
and will not affect visibilities. Winds will shift from the
northwest to the west overnight before turning southwest in the
early afternoon Friday. Gust of 15-20 kts are expected in the
afternoon tomorrow.


Dry VFR for the entire forecast period. There are some patches of
MVFR around the STL metro but should be moving out of the area by
TAF valid period, so they were kept out of this forecast. Winds
will back from the northwest overnight to a gusty west wind in the
late morning Friday. Gusts of 15-20 kts are possible. Winds will
decrease and turn to the southwest Friday evening.



Saint Louis     29  43  33  58 /   0   0   0   0
Quincy          25  40  30  54 /  20  20   0   0
Columbia        28  43  32  58 /   0   0   0   0
Jefferson City  29  44  31  60 /   0   0   0   0
Salem           26  40  29  53 /   0   0   0   0
Farmington      25  43  29  56 /   0   0   0   0




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