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fxus63 klsx 202349 
afdlsx

Area forecast discussion...updated aviation
National Weather Service Saint Louis MO
549 PM CST Wed Nov 20 2019

Short term... (through late Thursday afternoon)
issued at 257 PM CST Wed Nov 20 2019

The mid-Mississippi Valley is currently situated beneath an upper
ridge, with surface high pressure to our east and developing low
pressure to our west. The surface low will slide to the northeast
overnight as a shortwave embedded in SW flow pushes through the
Midwest. The forcing provided by the wave, coupled with strong low
level warm, moist advection, will be sufficient to generate
widespread precip beginning this evening in western MO before
moving east of the Mississippi late tonight. Precip will taper off
tomorrow morning beneath weak mid level height rises, though
another round of more scattered showers are expected tomorrow as
the cold front trailing the previously mentioned low sweeps
through the area. Temperatures will remain quite warm ahead of the
front thanks to the strong southerly flow, and some guidance is
even showing weak insatiability building in between the initial
widespread showers and more scattered precip along the front.
Therefore have introduced a period of low thunder chances tomorrow
morning and into the early afternoon.

Bsh

Long term... (thursday night through next wednesday)
issued at 257 PM CST Wed Nov 20 2019

Another embedded shortwave will move through the region on
Thursday night as the upper level jet intensifies. These features,
coupled with continued moisture advection along the baroclinic
zone, which at this time will be situated just south of the I-44
corridor, will result in another round of widespread rain across
southern Missouri. Rain activity in this area will again persist
through much of the night until the wave moves out of the area and
frontogenetical forcing weakens/moves out on Friday morning.
Colder air will be moving into the region at this time, but precip
should be confined to areas which will only support liquid precip.

Friday looks to be relatively dry until a weakening closed upper
low pushes toward the region in the afternoon. This low will help
deepen a surface trough over OK, which in turn will shunt the
baroclinic zone back into southern MO. The coupled forcing along
the front and passing upper trough may be enough to support light
precip in southeast MO and southern Illinois into Saturday morning. In fact,
most deterministic guidance, along with gefs and wpc ensemble
means do show at least a few hundredths in these areas. Cold air
will continue to filter into the region through the day on Friday
and into Saturday, and temps may be cool enough to support a brief
period of light snow on Saturday morning.

Dry northwest flow will begin to take over on Saturday, with high
pressure passing to the south of the region on Sunday. This will
result in a period of dry weather, with cool and cloudy
conditions on Saturday turning warmer more sunny by Sunday and
Monday. Meanwhile, a long wave trough will build into the western
conus, which will shift US into a more active pattern toward
mid week. While a storm is likely to impact the central portion of
the country during this time, model consensus is poor and forecast
details remain murky.

Bsh

&&

Aviation... (for the 00z tafs through 00z Thursday evening)
issued at 529 PM CST Wed Nov 20 2019

Showers now entering western Missouri will move east and reach
KUIN/kcou between 05-08z and the St. Louis area terminals around
08z. Ceilings will initially be VFR, but will drop to MVFR by 12z
and then remain that way through the remainder of the period. The
initial batch of rain will move out during the morning hours, but
additional showers will be possible during the afternoon,
particularly along and south of I-70. Any showers may reduce
visibilities into the 3-5sm range during the period. There will
also be 45kt winds between 1000-2000ft above ground level tonight, though surface
winds will remain high enough to keep low level wind shear too marginal to mention
in the tafs.

Specifics for kstl:

Showers over western Missouri will move into the terminal after
06z. Ceilings will initially be VFR, but will drop below 3000ft by
12z and remain MVFR the rest of the region. While there will be a
lull in the rain in the morning, there will be a chance of showers
there rest of the period. Any showers may reduce visibilities
into the 3-5sm range during the period. There will also be 45kt
winds between 1000-2000ft above ground level tonight, though surface winds will
remain high enough to keep low level wind shear too marginal to mention in the
tafs.

Britt

&&

Lsx watches/warnings/advisories...
MO...none.
Illinois...none.
&&

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