Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 241050

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
450 AM CST Fri Feb 24 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 343 AM CST Fri Feb 24 2017

Dynamic winter storm system tracking across the Midwest early this
morning toward the Great Lakes will bring an abrupt end to the
spring-like and record breaking temperatures that the region has
been enjoying the past week. Isolated to widely scattered showers
and thunderstorms will begin to develop along the cold front this
afternoon, especially across south central Illinois. That being
said, the greatest threat of this surface based convection becoming
severe continues to be nudged further east, concentrated over
Indiana and Ohio.

The harsh reality that it is still February will be realized late
this afternoon and this evening as temperatures plummet into the 30s
and a northwest wind gusting to 30 mph creates wind chill values in
the teens and 20s. To top it off, I wouldn`t be surprised if the
northern half of the CWA isn`t clipped with the tail end of the
storm system with rain showers turning to light snow showers
/flurries tonight. Welcome back winter.


.LONG TERM...  (Saturday through Thursday)
Issued at 343 AM CST Fri Feb 24 2017

Deep cyclonic flow will be present throughout the upper and mid MS
Valley region early Saturday morning in the wake of the exiting
system. The attendant gusty northwest winds and pronounced CAA will
be a big change compared to the unseasonably warm weather of late,
and it will feel rather chilly given the gusty winds and first
occurrence of below normal temps in several weeks. Some flurries
will be possible during the morning accompanying the lingering
post-frontal stratus. Clouds will clear during the day with winds
diminishing late in the afternoon. A rather fast quasi-zonal flow
will evolve across the Nation`s midsection heading into Saturday
night with surface high pressure sliding across the area. Like
Saturday`s high temperatures, the min temps early Sunday morning
will be the lowest in several weeks. The cold weather will be
short-lived however as a WAA regime evolves beginning on Sunday in
the wake of the departing surface high.

The aforementioned quasi-zonal flow will result in some forecast
issues heading into the first half of next week, with some
significant models differences in the timing of the fast-moving low-
amplitude short-waves. There is actually decent agreement on the
first of these on Sunday. Rather impressive ascent associated with
this short-wave and low level WAA should bring predominately a round
of rain to the region from late morning into the afternoon, exiting
to the east-southeast during the evening. After the passage of this
system however, the models diverge with the ECWMF rather agressive
showing large scale ascent and precipitation already spreading
back into the area on Monday morning within the WAA regime.
Alternatively the GFS is slower with the onset of precipitation on
Monday evening. The current forecast is a blend of the guidance
with a bit greater weighting on the slower GFS solution. A more
prominent migratory upper trof and associated surface low and
cold front are then expected to traverse the region Tuesday and
Tuesday evening bringing showers and possibly a few thunderstorms.



.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 445 AM CST Fri Feb 24 2017

Cold front has just moved through KCOU and is anticipated at KUIN
shortly after 12Z and St. Louis Metro sites by the lunch hour (16
to 17Z). Wind will shift from south to west/northwest and
increase. IFR ceilings currently plowing east behind the front in
central Missouri will likely scatter and lift as the dry slot
moves overhead this afternoon with another round of IFR stratus
tonight into Saturday morning. Also could see some light rain/snow
showers tonight as the storm system wraps up to our northeast.


Cold front should reach the terminal around 16:30Z with a wind
shift to the west and steady increase in speed through the
evening. Initial band of stratus currently behind the front may
scatter out before reaching KSTL in dry slot, with another batch
of stratus moving into the region this evening. Also could see
some light rain/snow showers tonight. Improving conditions
expected by Saturday afternoon with skies lifting/scattering. It
will remain windy until Saturday evening.



Record Highs


STL: 81/1930
COU: 81/1930
UIN: 73/1930

Record High Minimums


STL: 58/2000
COU: 61/1930
UIN: 55/1930




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