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Area forecast discussion...updated aviation
National Weather Service Saint Louis MO
533 am CST Tue Dec 10 2019

Short term... (through late Wednesday afternoon)
issued at 314 am CST Tue Dec 10 2019

Temperatures were close to seasonable normals early this morning
under broken cirrus. Winds were out of the northwest on the
northeast periphery of the surface high centered over plains. The
cirrus is expected to gradually push slowly south today as
longwave trough over the central Continental U.S. Slowly moves to the east.
Dry weather is expected to continue through tomorrow as
aforementioned surface high moves across Missouri and Illinois.
There will be a weak shortwave trough that will move across the
upper Midwest late tonight, but any precipitation with it is
expected to stay north of the area.

Highs today will remain below normal given the cold start, cold air
advection, and early clouds. Lows tonight fall back below normal
with strong radiational cooling. Highs tomorrow will climb back
to normal under sunny skies.


Long term... (wednesday night through monday)
issued at 314 am CST Tue Dec 10 2019

Dry weather is expected to continue Thursday and Friday as both the
deterministic and ensemble GFS/European model (ecmwf) are showing quasi-zonal
upper flow over the area. At the same time a large surface high
will move off to the east of Missouri and Illinois allowing the
surface flow to turn out of the southwest. This will allow
temperatures to climb back above normal by Friday. Quantitative precipitation forecast output from
the models and the ensemble plumes are not depicting any
precipitation chances until the weekend when the gefs and European model (ecmwf)
eps are showing a series of shortwave troughs moving across
Missouri and Illinois. The first two will move across the area
early in the weekend which will have an attendant cold front move
across the area Friday night/early Saturday causing the above
normal temperatures late in the week to fall below normal by
Sunday. Will continue with a chance of rain/snow Friday
night/Saturday with the best chance of snow north of I-70. Another
chance of precipitation will occur late Sunday into Monday in
broad warm air advection ahead of the next trough that will move
through early next week. While there remains a large spread
depicted in the gefs plumes, most of the solutions are below
freezing except over the southern cwa, so will go with a chance of
snow. However, because of the wide spread in the ensemble members
and the differing deterministic model solutions this far out,
will continue to go with just chance pops for late Sunday into
Monday at this point.



Aviation... (for the 12z tafs through 12z Wednesday morning)
issued at 520 am CST Tue Dec 10 2019

Northwest winds will continue to usher generally dry air into the
region through tomorrow. This will result in continued VFR
conditions through the duration of the taf period with just a few
features of note Worth discussing. First up, there is an area of
patchy 3-6 kft stratus pushing into northwest MO and will likely slide
into roughly the northern half of our area before scattering out
later this morning. Secondly, yet another area clouds will push
into northern MO and central Illinois tomorrow morning as a reinforcing
thrust of cold air moves into the upper Midwest. These clouds will
likely only reach as far south as uin, and are not expected to be
below 3 kft.



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