Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 180303

903 PM CST Mon Nov 17 2014

Issued at 902 PM CST Mon Nov 17 2014

Satellite is showing some clouds are moving across the northern
CWA at mid evening which should shift southeast of the CWA
overnight. Temperatures have fallen into the teens over much of
the CWA already with dewpoints well down into the single digits.
Did adjust temperatures downward slightly over central MO where
winds may become lighter in closer proximity to the surface high.
Otherwise forecast still looks good.



.SHORT TERM:  (Through Late Tonight)
Issued at 318 PM CST Mon Nov 17 2014

Deep trof over the eastern CONUS has hit bedrock and is continuing
to dig.  Can`t remember anything this strong or cold impacting the
area this early in the season within my 15 year tenure at WFO St.
Louis.  Indeed record lows will be in jeopardy tonight at St. Louis
(14/1932), Columbia (8/1891), and Quincy (7/1903).  Normally, would
expect these kind of temperatures to be possible only under
excellent radiational cooling conditions with light wind and a clear
sky.  However, the Arctic airmass which is building into the
Mid-Mississippi Valley produced lows in the single digits to low
teens this morning in eastern Nebraska even with winds in excess of
10kts.  Decided to be conservative and not follow the coldest
guidance, rather used a blend of MAV/MET MOS guidance and blended
ensemble MOS for lows.  This still yields lows right around the
aforementioned records.


.LONG TERM:  (Tuesday through Next Monday)
Issued at 318 PM CST Mon Nov 17 2014

(Tuesday through Thursday)

Specific temp trends remain the primary forecast concern into the
end of the week, although broad and unseasonably strong upper level
trof over the central and eastern half of the CONUS certainly points
to temperatures remaining well below average during this period.

Model forecasts of synoptic scale temperature profiles are fairly
similar, suggesting AMS modification across the FA in the
Tuesday-Tuesday night time frame as the chunk of Arctic air
currently over the area shifts east.  Shortwave dropping down the
back side of the trof will then bring a reinforcing shot of cold air
into the area on Wednesday which will then linger into Thursday.
Over the past 2 days NWP output has been very consistent in the
message that this next round of cold air will be nowhere near as
cold as what we`ve experienced over the last 24 hours.

While synoptic trends between the solutions are similar MOS output
does vary considerably on the daytime highs, with MET guidance
consistently running several degrees cooler than the GFS-based MAV
output.  Based on time of year as well as verification so far this
November that indicates GFS-based MOS has been the best guidance for
max temps, will lean towards the warmer MAV numbers.  This thinking
is also strongly supported by current temps over the plains, where
925 temps progged into SW parts of our CWA tomorrow are currently
supporting readings near 30. Increasing WAA Tuesday night ahead of
the next cold front will likely mean a limited, early evening temp
drop followed by steady or slowly rising temperatures during the
overnight hours, and this trend is already reflected in going
forecasts.  For the arrival of the next round of cold air on
Thursday have not made many changes to going temps, which will
continue to favor the warmer MAV guidance in the weaker/less intense
CAA over southeast sections of the CWA.

Cold and tranquil weather expected Wednesday night and Thursday as
the narrow surface ridge works into the area, with lows in the teens
and low 20s and highs primarily in the 30s.


Medium range solutions are still forecasting the mid-Mississippi
Valley to come under the influence of the southern branch of the
westerlies heading into next weekend as deep upper trof sweeps
east and begins to lift out. Models are now suggesting a very weak
shortwave possibly impacting the region as early as Friday, but
they remain in good agreement that a much stronger system
embedded in the southern stream will impact the region over the
weekend. Will introduce a bit of precip across the area Friday and
Friday night with this first impulse, and since the ams over the
region will still be fairly chilly and dry at this time will make
this precip a light wintry mix. However, by the time the main
system arrives on Saturday, AMS should warm enough to keep precip
in liquid form. Have also introduced a chance of thunder over
southeast sections of the CWA based on instability progs of GFS
and ECMWF.

Transition in the UA pattern should also mean moderating temperatures,
with readings finally returning to near average levels by Sunday.



.AVIATION:  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 516 PM CST Mon Nov 17 2014

SC and gusty northwest winds to diminish early this evening.
Otherwise, winds to pick back up by mid morning on Tuesday with
gusts near 20kts at times with scattered diurnal cu once again.

Specifics for KSTL:
SC and gusty northwest winds to diminish early this evening.
Otherwise, winds to pick back up by 16z Tuesday with gusts near
20kts at times with scattered diurnal cu once again.




The following are record low maximums and record low minimums
through Tuesday.

Date:       11/17     11/18

               St. Louis

Low High:  17/1880   25/1880
     Low:   6/1959   14/1932
Snowfall: 1.0/1951


Low High:  23/1959   27/1903
     Low:   4/1959    8/1891
Snowfall: 0.1/1989


Low High:  19/1959   24/1903
     Low:   3/1959    7/1903




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