Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 220430

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1130 PM CDT Mon Oct 21 2019

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 321 PM CDT Mon Oct 21 2019

A strong surface low across eastern Minnesota will slowly lift
northeastward toward Lake Superior by Tuesday afternoon. This will
act to keep a tight pressure gradient across the bi-state region.
Winds will slacken slightly tonight before re-intensifying behind
a secondary cold front which is expected to move through by
Tuesday morning. Sustained westerly wind speeds of around 20 mph
with gusts of 25-35 mph are forecast, with the highest values
across northern sections of the forecast area.

Temperatures are forecast to be seasonally cool through Tuesday
night. Lows tonight should be mostly in the low to mid 40s, with
highs on Tuesday in the upper 50s to low 60s. Continued to lean a
bit toward the warmer MAV guidance for highs tomorrow due to deep
mixing and plentiful sunshine across much of the region, though
strengthening low-level cold air advection behind the secondary cold
front will help to offset these factors. Portions of northeast
Missouri and west-central Illinois may also get clipped by the
south/southwestern edge of the wraparound stratus. If this were to
occur and linger long enough during the day, readings in these
locations may end up being a couple of degrees cooler than forecast.
A crystal clear sky is expected Tuesday night along with lighter
winds as a surface high approaches from the south-central Plains.
These conditions should be favorable for radiational cooling
resulting in lows several degrees cooler than tonight. Temperatures
Tuesday night are forecast to bottom out in the upper 30s to low 40s
across the area.


.LONG TERM...  (Wednesday through Next Monday)
Issued at 321 PM CDT Mon Oct 21 2019

Models agree better with the evolution of the next cold front on
Wednesday/Wednesday night and its associated surface low tracking
north of the Great Lakes. This front should pass through the region
by Thursday morning. Ahead of this front, temperatures on Wednesday
should rebound back into the mid 60s to low 70s which is near to
slightly above normal. This front is expected to slow its
equatorward progress Thursday and Thursday night and at least some
energy ejecting out of the southern Plains is forecast to bring a
chance of light rain to the region Thursday/Thursday night. The
deterministic GFS/ECMWF continue to diverge on how to handle this
aforementioned energy. The ECMWF for several runs now has closed
this system off before ejecting it out early this weekend. This has
some support from the operational CMC as well. However, the GFS is
more progressive, moving this shortwave trough through the area
Thursday night. Looking at the GFS ensemble members, all of them
behave like the operational run, progressing this shortwave trough
into the Ohio Valley by Friday morning. All this being said,
certainly a low confidence forecast, particularly Thursday night
through Sunday. If the system is progressive like the GFS suggests,
dry and cooler than normal weather would be in store Friday through
Saturday. The ECMWF, with its cutoff low forecast ejecting out on
Saturday, would likely result in milder temperatures along with
another round of rain for this upcoming weekend. For now, leaned
toward the GFS solution based on climatology and high agreement with
its ensemble members but kept a mention of light rain for this
weekend in case the slower, cutoff solution which the ECMWF/CMC
suggest does indeed verify.



.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1121 PM CDT Mon Oct 21 2019

Dry and VFR conditions are expected through the period. West to
southwest winds will continue with gusts increasing again to 20
to 25 knots at times during the day on Tuesday before winds
diminish to less than 10 knots on Tuesday evening.





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