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Area forecast discussion 
National Weather Service Kansas City/Pleasant Hill MO
541 am CST Mon Dec 22 2014

Short term...(today through wednesday)
issued at 336 am CST Monday Dec 22 2014

Challenging short term forecast as deep upper trough continues to
take form over the central U.S. This morning. Quick look at am water
vapor imagery reveals the presence of several shortwave troughs
embedded in northwest flow across the central/northern rockies. With
time today...these impulses will begin consolidating into a closed
upper low across the Central Plains and lower Missouri Vly. All
available guidance agrees that once developed...this feature will
take its time leaving our area as ridging along the East Coast
creates a temporary blocking pattern across the lower 48. As a
result...it appears a fairly unsettled period is in store for our
region as we head into the the first half of the Holiday work week.

Regional radars this morning showing developing shwr activity off to
our west as the first shortwave trough approaches. Furthermore...a
weak warm front analyzed across central OK this morning is progged to
begin lifting northward today as elongated sfc low/trough across the
plains slowly shifts eastward. Height falls combined with modest
isentropic upglide should keep the threat for rain shwrs going
through a good portion of the day today...and categorical pops have
been offered region-wide.

Tonight...drier air should begin working into the area from the
south as warm front slowly lifts north with time. Despite
this...additional shortwave energy arriving from the
northwest...along with an approaching cold front...will lead to
continued lgt shwr activity along and north of the I-70 corridor.
Colder air should begin filtering into the region after midnight
following the passage of main cold front. As this occurs...rain may
mix with snow and eventually all snow up north along the Iowa state
line. For now...best chance for any accumulations looks to be far
northwest MO where up to a half inch will be possible. Further south
towards the kc Metro...little to no accumulation is expected as
forecast temp profiles remain warm enough to support liquid precip.

Tuesday and Tuesday ngt...main sfc low to gradually lift northeast
towards the western Great Lakes with cold air advection expected in
its wake. Aloft...main upper low to be positioned directly overhead
with models showing developing shwr activity once again as main mid-
level vort Max and low-level trough axis approach. Best chance looks
to be across the northwestern County Warning Area where chc pops have been maintained.
Any snow shwrs early tues morning should begin changing to rain as
daytime heating commences. GFS most aggressive in maintaining precip
across the area Tue night as main low-level trough axis continues
sliding through. If this occurs as advertised...the whole County Warning Area stands
to see developing snow shwrs overnight as the thermal column cools
enough to support all snow. Right now...have kept accumulations
under 1" across all areas.

Wed/Wed ngt...weak sfc ridging to begin building in through the day
behind main quantitative precipitation forecast axis that should continue sliding east with time.
Temps through the day will reside in the lower to middle 30s which
may support a few light snow shwrs or flurries /eastern cwa/. Dry wx
to finally return Wed night as weak shortwave ridging builds
overhead.

Long term...(thursday through sunday)
issued at 336 am CST Monday Dec 22 2014

The extended forecast will start out relatively warm before
reverting back to near normal conditions through the remainder of
the period. Conditions will also remain fairly benign as there is
only one weak system of interest.

Models are in good agreement through the Thursday through Friday
night timeframe in depicting upper level troughing over the eastern
Continental U.S. With weak upper level ridging building over the central Continental U.S.
In response to a upper trough digging through the Great Basin. This
ridging over the central Continental U.S. Acting in concert with strong
southerly flow will provide for a relatively warm Christmas day.
Expect highs in the low 40s to near 50. This warm up will be
short-lived however, as the Great Basin trough moves through the
northern plains on Friday forcing a cold front through the area
early in the day. Strong cold air advection behind the front will
keep highs in the lower 30s to lower 40s on Friday. Also, behind the
front on Friday there will be the potential for a mix of light rain
and snow across northern Missouri however, little to no accumulation
is anticipated as moisture is meager with this system. This system
will be a quick moving system and will push northeast of the
forecast area Friday night.

Model solutions begin the diverge as we get into the weekend. The
GFS tries to flatten out the upper level flow across the Continental U.S. With
a weak and progressive shortwave trough traversing north of the area
on Sunday and Sunday night. Whereas the GFS shows a more zonal
pattern for the beginning of weekend, the ec is more amplified. The
ec holds a piece of energy from the upper level system, that moves
north of the area on Friday, back across the eastern rockies.
Saturday, this energy, in the form of an upper level trough, will
dig as it moves through the central and Southern Plains. Surface
high pressure over the area Saturday into Saturday night (the GFS
also depicts this) should keep the bulk of the precipitation
associated with this system shunted to the south however, the
southeastern part of the County Warning Area would experience light snow if the ec
solution came to fruition. In regards to the late weekend system the
GFS pushes north of the area, the ec is much slower and deeper with
this trough and it remains well west of the forecast area by the end
of the period. Temperatures Saturday through Sunday will mainly be
in the 30s to near 40 which would be near normal for the end of
December.

&&

Aviation...(for the 12z tafs through 12z Tuesday morning)
issued at 540 am CST Monday Dec 22 2014

Long duration IFR conditions expected today as a slow moving storm
system meanders across the lwr Missouri Vly. Most terminals already
reporting IFR cigs and stj will likely fall very shortly. Some
potential for cigs to fall below alternate mins at mci later today
but overall confidence of this scenario remains marginal. At
remaining sites...alternate min thresholds look more likely due to
slightly higher thresholds. Accompanying the low cigs will be periods
of rain which should last through the mid/late afternoon hrs.

Towards 00z...expect winds to gradually start veering to the west
following a cold front passage. Fcst models suggest some drier air
will work into the area which may allow cigs to climb back towards
low-end MVFR. Despite this...cannot rule out some lgt rain/snow shwrs
at stj...but will address with later updates pending the arrival of
additional model data.

&&

Eax watches/warnings/advisories...
Kansas...none.
MO...none.
&&

$$

Short term...32
long term...73
aviation...32

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