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fxus63 klsx 180004 

Area forecast discussion...updated aviation
National Weather Service Saint Louis MO
604 PM CST sun Nov 17 2019

Short term... (through late Monday night)
issued at 219 PM CST sun Nov 17 2019

A cold front was moving through the region this afternoon
accompanied by a band of light rain which was being driven by
frontogenetical forcing in the presence of large scale ascent
ahead of a pv anomaly. The band of rain will continue moving
across the area as the upper trough moves through, and it may
even weaken with time based on model forecasts of decreasing
frontogenesis. Extensive cloud cover will remain across the area
behind the cold front, and this will keep overnight lows warmer
than they would have been otherwise. Overnight lows will range
from the low 30s in NE MO to the mid/upper 30s in southeast MO and S Illinois.

Model guidance depicts another pv anomaly quickly approaching the
area on Mon, and this feature could bring light rain to the area
on Mon aftn/eve as it moves through the region. Some model
guidance actually depicts this feature as a pair of pv anomalies
with the lead pv anomaly being weaker and located slightly farther
southeast than the other one. Regardless, the passage of at least
one pv anomaly is enough to justify maintaining low pops for Mon
aftn/eve with pops spreading from west to east. Highs on Monday
will be similar to Sunday across most of the area and a few
degrees warmer than Sunday for much of central and southeast MO. Given
these warmer temperatures, the precipitation type on Mon aftn/eve
would likely be rain.


Long term... (tuesday through next sunday)
issued at 219 PM CST sun Nov 17 2019

A more noticeable warming trend will begin on Tue and persist
through Thu thanks to an upper ridge which shifts eastward and a
surface high which shifts southeastward. The resulting
combination of rising heights aloft and favorable S/SW flow at the
surface will boost highs into the 50s and 60s during this time,
which will be 5-10 deg above normal for most of the region. A cold
front then moves through the region on Thu, bringing daily highs
back down into the 40s to near 50 for the next few days.

If heights are rising in the central conus, then they must be
falling somewhere else...and in this case, it's the western Continental U.S..
model guidance is in reasonably good agreement regarding 3
features: 1) a strong pv anomaly which moves onshore over or/Washington
around 06z Tue, 2) a separate pv anomaly which then dives into
the back side of the resulting trough, and 3) a cutoff low which
will be located off the western coast of Baja California. The
interaction between these features will lead to a deep trough
developing over the western Continental U.S. During the middle and end of the
week. Model guidance is in good agreement that the formerly
cutoff low near Baja California is eventually ejected
northeastward through the central Continental U.S. And interacts with a
northern stream trough axis. Although model guidance shows more
variability with the evolution and eventual disposition of the
resulting large cutoff low over the western conus, it too should
eventually shift eastward into our region. Taken together, this
means that there will be a couple of opportunities for widespread
precipitation during the upcoming week. The first is from Wed
aftn through Thu evening and is associated with the formerly
cutoff low near Baja California as it lifts through the region and
drags a cold front through MO/IL. Based on thermal profiles, most
of the precipitation should fall as rain with this system. The
second opportunity is from Fri night through Sat night and is
associated with the approach/passage of the larger low.
Temperatures will be colder with this second system compared to
the first, and a rain/snow mix is not out of the question at times.
That said, there is greater uncertainty regarding all aspects of
this system (temperature and precipitation) because of the
aforementioned model variability.



Aviation... (for the 00z tafs through 00z Monday evening)
issued at 551 PM CST sun Nov 17 2019

An upper level disturbance combined with a weak trough of low
pressure at the surface is moving through the area this evening.
This system is producing an area of light rain that is moving east
at around 25kts and it should be out of the area into east central
Illinois by about 900 PM. Areas of MVFR ceilings will
intermittently affect central and eastern Missouri into western
and central Illinois through tonight...particularly across
northeast Missouri into west central Illinois. The ceilings are
expected to scatter out over parts of central Missouri late
tonight...and with light wind we could see some fog develop.
Confidence isn't particularly high on fog development, but it's
possible visibility could drop to IFR in central Missouri before
sunrise. Any fog that does develop should dissipate by mid

Specifics for kstl:

Rain should be ending shortly at Lambert...and then VFR conditions
are expected to prevail. I think there will be some intermittent
MVFR for a few hours this evening as a weak surface trough moves
through combined with a stronger upper level disturbance, but
latest guidance isn't really excited about MVFR overnight.
Therefore expect VFR cigs through the overnight hours continuing
into Monday.



Lsx watches/warnings/advisories...

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