Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 071746

1146 AM CST SUN FEB 7 2016

.SHORT TERM: (Through late this afternoon)
Issued at 320 AM CST Sun Feb 7 2016

Enjoy today if you like mild temperatures. It will be the last one
like it for at least a week. Big changes on the way over the next
24-36 hours and a return of winter cold in response to tremendous
large scale amplification of the upper air pattern. Two short wave
trofs of interest early this morning, one moving through the upper
MS Valley and another moving out of Saskatchewan into the northern
Plains. The lead wave will weaken and shift eastward into the
Great Lakes this morning while the trailing wave will deepen and
dig rapidly southeastward thanks to an attendant 125+ kt ULJ. This
wave will reach the Mid MS Valley by 00Z, and will drive a front
through the CWA beginning after 15z. Veering southwest-west winds
ahead of the front, continued low level WAA, and relatively mild
early morning temps should allow most locations to climb into the
50s before the fall begins during the later afternoon. There is
still some question as to whether we will see any precipitation
today along/ahead of the front. Large height falls/increasing
large scale ascent and moisture during the afternoon associated
with the upper system may be sufficient to generate spotty showers
across east central/southeast MO into southwest IL in the 21-03z
time frame.


.LONG TERM: (Tonight through Saturday)
Issued at 320 AM CST Sun Feb 7 2016

A secondary cold surge/front, denoted by increasing and gusty
northwest winds and trofing the cyclonic surface flow, will enter
the area later in the evening bringing strong CAA and much colder
temperatures, and some snow. Monday will be a Winnie The Pooh type
day with cold, blustery conditions. The coverage of snow is the
biggest question mark. Model QPFs are rather light through 00z
Tuesday, and numerous CAMs showed narrow cyclonically curved bands
overnight Sunday into Monday. Model soundings indeed show favorable
shear and stability profiles for horizontal convective rolls in
the lowest 10 kft. This would suggest some spots could get no more
than a light dusting while others might see snow accumulations of
up to an inch.

Below average temperatures and cold will dominate Tuesday and
Wednesday as a deep expansive upper trof dominates the eastern
2/3rds of the Nation. During the later part of the week and into
the weekend, heights aloft rise as the amplitude of the trof
diminishes and becomes more broad, with flow aloft backing from
NNW to WNW. This would suggest at least some moderation of
temperatures, however maybe not as much as the GFS and MEX MOS
might suggest. The ECMWF is much colder with sharper cyclonic
curvature to the flow aloft, allowing another cold surge on Friday
that lasts into the weekend.



.AVIATION:  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1130 AM CST Sun Feb 7 2016

Specifics for KCOU, KUIN: VFR for the first 0-6 hours and possibly
longer. MVFR stratus is expected to reach the terminals after 03z.
Snow showers will develop overnight and persist through the end of
the TAF period. Transient IFR vsbys are possible at times when the
heavier snow showers move directly over the terminals, but it is
not possible to pin down a more exact window this far in advance.

Specifics for KSTL, KSUS, KCPS: VFR for the first 0-6 hours and
probably for the first 0-12 hours. A cold front was moving
through the St. Louis metro area at TAF issuance. Winds were
gradually turning westerly behind the front and wind gusts had
increased to around 25 kts. MVFR stratus is not expected to reach
the St. Louis metro terminals until after 06z. Snow showers will
likely develop early tomorrow morning and persist through the
afternoon. Transient IFR vsbys are possible at times when the
heavier snow showers move directly over the terminals, but it is
not possible to pin down a more exact window this far in advance.





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