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fxus63 klsx 212351 
afdlsx

Area forecast discussion...updated aviation
National Weather Service Saint Louis MO
551 PM CST Thu Nov 21 2019

Short term... (through Saturday morning) issued at 316 PM CST
Thu Nov 21 2019

The middle Mississippi Valley is currently situated between a
sharp upper trough extending from the Hudson Bay into the upper
Midwest and a broad closed upper low over the Desert Southwest. A
cold front associated with the upper trough to the NE is passing
through the region with the upper portions of that front
extending North Well into the forecast area. A shortwave will
eject into the Midwest/mid-south tonight, enhancing mid and low
level forcing along the stalling front, igniting another round of
widespread precip along the baroclinic zone. Precipitation is
very likely across southern MO and IL, with the northern extent of
the precip determined by the advance of cool, dry air behind the
front. Forecast guidance has zeroed in on roughly the I-70
corridor as the delineator between a wet and dry forecast
overnight.

As the shortwave kicks east of the region on Friday, cool and dry
air will continue to move further south into the area. This dryness,
coupled will weak subsidence behind the departing shortwave, will
keep a lid on precip chances on Friday. It will also result in
considerably cooler temperatures on Friday, despite gradually
clearing skies across much of the forecast area. Meanwhile, the
southwest cutoff low will approach the region. This will deepen a
surface trough across OK and AR, which in turn will shunt the
baroclinic zone back into southern MO and Illinois beginning late Friday
afternoon. The forcing along the front, along the the DCVA
provided by the upper low, will likely be sufficient to result in
additional precipitation.

Forecast guidance is slowly coming into consensus on the precip on
Friday night and Saturday morning. Many of the deterministic and
ensemble members are pushing measurable precip across nearly the
entire forecast area, with several forecasts showing the highest
amounts in excess of 0.2" of liquid into southeast MO and southern Illinois. With
cooler air continuing to filter into the region, thermal profiles
appear to be supportive of light wintry precipitation on Saturday
morning. A mix of rain and snow appears to be the most likely precip
types, but we're beginning to see subtle hints that a small amount
of freezing rain may even mix in. Given the marginal thermal profiles
and warm ground, I don't expect to see much more than up to a half
an inch of snow on grassy and elevated surfaces.

Bsh

Long term... (saturday through next thursday)
issued at 316 PM CST Thu Nov 21 2019

Dry northwest upper level flow will take over by Saturday as surface high
pressure begins to build into the area. This will result in dry
weather, with continued cool temps on Saturday and warming temps
on Sunday and Monday thanks to increasing southerly winds. The
pattern is then expected to turn more active by Tuesday as an
upper level trough moves into the region. Uncertainty on forecast
specifics is fairly high given considerable model spread, but
this pattern is most likely to result in precipitation across the
region. Fortunately the bulk ensemble guidance keeps temperatures
largely above freezing during this period, so chances for wintry
precip in the mid-Mississippi Valley appears to be rather low. On
the other side of that Coin, cips severe analogs have been creeping
a small risk of severe weather into the region on Tuesday, which
depending on how robust of a system develops, is not out of the
question. Dry northwest flow is then expected to build back into the
region by the end of next week, resulting in another period of
quiet weather.

Bsh

&&

Aviation... (for the 00z tafs through 00z Friday evening)
issued at 531 PM CST Thu Nov 21 2019

Overcast ceilings between 1500-2500ft above ground level are expected through
09-12z at KUIN/kcou and the St. Louis area terminals through late
tomorrow morning. Rain currently over southwest Missouri is
expected to move into northeast into parts of eastern Missouri and
southwest Illinois later tonight into early Friday including the
St. Louis area terminals. The rain is expected to move out of the
area by mid morning and VFR conditions are expected by Friday
afternoon.

Specifics for kstl:

Overcast ceilings between 1500-2500ft above ground level are expected through
late tomorrow morning. Rain currently over southwest Missouri is
expected to move into terminal late tonight. The rain is expected
to move out of the area by mid morning and VFR conditions are
expected by Friday afternoon. Additional rain with MVFR conditions
will move back into the Airport late tomorrow evening.

Britt

&&

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

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