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fxus63 klsx 171152 
afdlsx

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

Short term... (through Monday night)
issued at 323 am CST sun Nov 17 2019

We are still expecting a band of rain to move across the area
today and into this evening, however the evolution and departure
this evening is slower than previously thought. The main changes
to the forecast for today incorporate this thinking and also
increase the probability of precipitation. Other than timing, the scenario hasn't
changed much. The combination of large scale ascent associated
with the deepening upper trof currently across the plains will
combine with increasing low-mid level frontogenetic forcing to
produce a northeast-southwest oriented band of rain across
western MO this morning. The band of rain will then progress
eastward into Central/Northeast MO and west central Illinois through the
morning as the upper trof moves into the MS valley, and then into
the remainder of eastern MO and southwest Illinois during the afternoon
and early evening. The rain will then exit the County Warning Area later this evening
as the upper trof continues digging eastward through the MS valley
and into the western Ohio/Tennessee Valley. This still looks like an all
rain event. There is plenty of warm air aloft and surface temperatures
in central and northeast MO are already above freezing. It will
remain a cool day with below average high temperatures. Clouds
will be slow to depart tonight and lows are expected to be above
freezing over all but a small portion of the northern County Warning Area.

It now looks like we could see some light rain Monday afternoon
and night. The previous few days the models had been showing some
spits of light quantitative precipitation forecast associated with a northwest flow short wave
trof however forcing had been a bit disorganized. This has
changed with the latest model runs, especially the European model (ecmwf) and NAM.
Both are showing a stronger clipper system and potential for a
northwest-southeast oriented band of rain resulting from better
large scale forcing, low level warm air advection, and frontogenetic forcing. I
have conservatively introduced some slight chance probability of precipitation into the
forecast across the western County Warning Area during the afternoon and much of
the County Warning Area during the evening. High temperatures will remain below
average owing to extensive cloudiness.

Long term... (tuesday through saturday)
issued at 323 am CST sun Nov 17 2019

We are still looking at a pattern change and nice warm-up
beginning on Tuesday. Heights aloft will be rising as the eastern
long wave trof departs, and ridging builds from the plains into
the region associated with large scale amplification anchored by
a deepening trof in the western U.S.. the combination of rising
heights aloft and backing low level flow/warm air advection should switch the
gears on temperatures with above normal highs on Tuesday. The
eastward migration of the upper ridge on Wednesday and resultant
backing flow aloft along with strong low level warm air advection should result
in high temperatures some 10-15 degrees above normal.

The deterministic models and ensemble means have come into much
better agreement Wednesday night through Thursday showing
northeast moving surface low with the associated cold front
approaching and moving across the County Warning Area. Rain looks rather
widespread with this system.

The deterministic models however quickly begin to diverge by
Friday with the handling of the split flow regime and especially
the evolution and eastward progress of the western U.S. Upper
low/trof. Spaghetti plots from the gefs are quite chaotic showing
considerable spread supporting the higher than normal uncertainty
and low confidence in the late Friday-Saturday forecast periods.

Glass

&&

Aviation... (for the 12z tafs through 12z Monday morning)
issued at 542 am CST sun Nov 17 2019

Fog reducing the visibility to 4-6sm will be possible across far
eastern MO and southwest Illinois through around 14z. Otherwise a band
of rain will develop across western MO this morning and move
eastward through the day and early this evening eventually
impacting all the terminals. Flight conditions will initially be
VFR at the onset of rain but will lower to MVFR within several
hours after and then remain at MVFR through most of the remainder
of the forecast period. The rain will be occurring along and
ahead of a cold front which will be accompanied by a west to
northwest wind shift.

Specifics for kstl:

Fog reducing the visibility to 5-6sm will be possible through
around 14z. Otherwise a band of rain will develop across western
MO this morning and move eastward through the day, impacting the
terminal from around 22-01z. Flight conditions may initially be
VFR at the onset of rain but will lower to MVFR within several
hours after and then remain at MVFR through most of the remainder
of the forecast period. The rain will be occurring along and
ahead of a cold front which will be accompanied by a west to
northwest wind shift.

Glass

&&

Lsx watches/warnings/advisories...
MO...none.
Illinois...none.
&&

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