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fxus63 klsx 161056 

Area forecast discussion...updated aviation
National Weather Service Saint Louis MO
456 am CST Sat Dec 16 2017

Short term... (through late tonight)
issued at 337 am CST Sat Dec 16 2017

Skies were clear across all of the County Warning Area early this morning. Surface
winds were staying out of the south to southwest between 5-15 mph
allowing temperature to stay at or above normal for the middle of
December. The upper ridge axis that is currently over the Central
Plains will move east toward Missouri and Illinois today. This will
act to keep the skies sunny throughout most of the day. The GFS/NAM
is showing a fairly tight pressure gradient today between high
pressure centered over the southeast Continental U.S. And a frontal trough
extending from low pressure over New Mexico northeastward into Iowa.
This should act to increase winds out of the southwest into the 10-
20 mph range during the day with higher gusts. The full sun and the
favorable wind direction should allow for warming above MOS and sref
mean temperatures today, so kept with going forecast temperatures.

Still looks like this evening will be dry, but there will be an
increasing chance of rain overnight over parts of central and
southeast Missouri as the upper low that is opening up approaches
the area. Both the GFS/NAM show a marked increase in low level
moisture convergence beneath mid level ascent associated with the
trough across these areas, most notably between 09-12z tonight. Have
gone with mainly chance pops except in a small part of the Eastern
Ozarks where I have likely/categorical pops. With the strong warm
air advection tonight, temperatures will stay above freezing across
the entire area.


Long term... (sunday through friday)
issued at 337 am CST Sat Dec 16 2017

The upper air pattern will evolve considerably through next weekend
consisting of a split flow while trending more amplified as well.

Perhaps the best threat of precipitation and with greatest
confidence will be early in the period on Sunday. The models are
very similar showing a short wave trof within the southern stream,
weakening as it ejects northeast across the area Sunday in response
to an upstream kicker. Rain associated with the northeast edge of
a large precipitation shield will likely be ongoing across
southern MO at 12z, impacting the southwest portion of the County Warning Area.
This shield of rain will quickly overspread the area on Sunday
morning as large scale ascent shifts northeast with the advancing
short wave trof. Present indications are that most of the rain
should be over by midday as the trof axis stretches thru central
Illinois at 18z with large scale subsidence by afternoon. Low clouds
should linger through Sunday night and into Monday morning and
there could be some drizzle or sprinkles across portions of
central and northeast MO on Sunday night. While Sunday will be
cooler due to clouds and morning precipitation as compared to
today, Monday looks be a return to above average temps, perhaps
well above average depending on clouds. There are some indications
a weak frontal boundary may be present at the start of the day
across northern MO and then the aforementioned stratus. However
southwest-west low level flow becomes prevalent with good warm air advection and
this should result in eroding clouds and frontolysis of any
thermal boundary should one be present.

The models begin to show there first sign of diverging with the next
cold front in the late Monday night-Tuesday time frame. The GFS is
basically about 6 or so hours faster bringing a cold front through
the area by Tuesday morning, a reflection of sharper, more
amplified northern stream troffing extending southward from a
Hudson Bay upper low. The GFS/ecwmf then diverge again with a
southern stream upper trof advancing eastward from the Southern
Plains and across the lower MS valley on Wednesday. The European model (ecmwf) is a
good deal stronger and further north and suggests roughly the
southern 1/4 to 1/3 of the County Warning Area could see light rain associated
with the northern part of the deformation zone precipitation
shield. Model agreement continues to go downhill during the later
part of the week with big differences between the GFS and European model (ecmwf)
handling the split flow, dominant stream, and location and
evolution of a southern stream upper low/trof. In general the
European model (ecmwf) has a more dominant northern stream and points to the
evolution of a broad deepening upper trof centered through the
nation's midsection by next weekend. The GFS on the other hand has
a less amplified northern stream with an upper low still back in
the southwest. Sometime in the Thursday/Thursday night time frame
there should be a rather strong cold front move across the region
and it could be accompanied by a Post-frontal band of wintry
precipitation. Confidence is very low in any details at this
point, but at face value it would appear that northern parts of
the County Warning Area would currently have the best chance of measurable snow on
Thursday night/early Friday morning.



Aviation... (for the 12z tafs through 12z Sunday morning)
issued at 449 am CST Sat Dec 16 2017

Low level wind shear conditions will diminish by mid morning as
the low level jet will decrease and southwesterly surface winds
will increase. Gusty southwest winds will increase across the
area by mid morning and last through sunset with gusts above 20kt.
Dry and VFR conditions are expected through late tonight before
an area of rain with low VFR and MVFR ceilings moves northeast
into the area.

Specifics for kstl:

Low level wind shear is expected to diminish by mid morning before
southwest surface winds increase with gusts above 20 knots most of
the day. Dry and VFR conditions are expected through 12z Sunday
before light rain moves into the terminal with low VFR or possibly
MVFR ceilings.



Fire weather...
issued at 427 am CST Sat Dec 16 2017

Unseasonably mild temperatures combined with a dry air mass will
result in low relatively humidity this afternoon with minimum
values of 20 to 30 percent. The low relative humidity values, southwest winds of
10 to 15 mph with higher gusts, and dry fuels will promote
heightened fire danger across central and eastern Missouri and
portions of western Illinois this afternoon.




issued at 334 am CST Fri Dec 15 2017

Record high temperatures for today, December 16, 2017

St. Louis 70 in 1889
Columbia 70 in 1889
Quincy 65 in 2006


Preliminary point temps/pops...
Saint Louis 62 40 49 41 / 0 10 80 10
Quincy 57 35 46 37 / 0 5 80 10
Columbia 63 38 48 39 / 0 20 80 10
Jefferson City 65 39 49 40 / 0 30 80 10
Salem 55 37 47 40 / 0 10 70 10
Farmington 58 38 48 40 / 0 40 80 10


Lsx watches/warnings/advisories...

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