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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
1152 PM CST Friday Dec 26 2014

Update...
issued at 940 PM CST Friday Dec 26 2014

Very light precipitation event underway with radar returns blossoming
west/southwest of quadrant cities and a few observation reporting sprinkles or
patchy very light rain. This is occurring with surge of isentropic
lift and convergence along front aided by approaching weak surface
low. Our County Warning Area for this event will largely remain in between
stronger forcing to our west/northwest lifting from the plains into the
upper Midwest... and deeper moisture plume (pwats approaching 1
inch) veering from MO through central Illinois. As result expecting very
light rain amounts where it does occur and generally from trace to
less than 0.1 inch. Still have chance of rain mixed with snow late
tonight into Saturday morning northwest County Warning Area... but some of the
latest model soundings showing considerable drying in middle levels
and thus would suggest more likely just a few flurries or possibly
patchy dz/fzdz depending on moisture depth and ice introduction.
As result...have continued to trim any snow accums northwest County Warning Area.

As for temperatures... will continue to see decent gradient across County Warning Area
with coldest readings (30-35f) west/northwest near and just on
cold side of front. Meanwhile many areas along and east of the
Mississippi River will remain in the 40s rest of tonight. Temperatures will
even rise a few more degrees to around 50 or lower 50s for a time late
this evening into early overnight from quadrant cities S/E.

Updated grids/zfp/pfm have been sent.

&&

Synopsis...
issued at 215 PM CST Friday Dec 26 2014

Another mild late December day with filtered sunshine through cirrus
clouds streaming northeast across the County Warning Area. 2 PM temperatures ranged
from the middle 40s far north to the middle 50s far south.

A nearly stationary strong frontal boundary extended from central WI
to central Iowa and then into the Texas Panhandle. Temperatures ahead of
the front were mainly in the 50s while behind the front readings were
only in the 20s to lower 30s. A band of snow extended from eastern
Colorado/western Kansas northeast into central/western Nebraska.

&&

Short term...(this evening through saturday)
issued at 215 PM CST Friday Dec 26 2014

Forecast focus on mainly light rain tonight then our recent stretch
of mild weather comes to a screeching halt on Saturday.

Tonight...operational models similar in tracking a weak low pressure
system from the Southern Plains into eastern Iowa by sunrise. This
puts the accumulating snow to the northwest of the dvn County Warning Area where the colder
air and better forcing will exist. Models also similar in keeping
the deeper moisture to our southeast with only light rain amounts expected
in the dvn County Warning Area...about a tenth of an inch or less. The higher probability of precipitation
will be Post-frontal as the cold front makes slow progress into
eastern Iowa overnight. Ahead of the front scattered showers should
develop especially after midnight. Forecast soundings indicate the
column cools below freezing in our far northwest County Warning Area towards morning but
by that time moisture is decreasing. So will continue to mention a
rain/snow mix late tonight then turning to all snow but if any accumulations
occur it would be a dusting on grassy surfaces. Another mild night
with minimum temperatures ranging from the lower 30s at Independence
Iowa to the middle 40s at Macomb Illinois.

Saturday...deepening low pressure tracks to eastern Upper Michigan by late
in the afternoon. Forcing along with 1000-500 mb mean relative humidity quickly decreases
in the morning thus will follow suit with decreasing probability of precipitation. The cold
front will sweep through the remainder of the County Warning Area during the morning
with colder/drier air filtering into the County Warning Area behind the front...so have
removed probability of precipitation for the afternoon. Also during the afternoon we will be
cold advecting and with cyclonic flow this will keep low clouds in place...
along with the dreaded falling temperatures. Highs on Saturday will
actually occur in the morning...ranging from the lower 30s northwest to the
middle 40s in our far eastern counties.

Long term...(saturday night through friday)
issued at 215 PM CST Friday Dec 26 2014

Main forecast concern for the extended forecast are the temperatures
and two systems forecast to move through the area. One system on
Monday into Tuesday looks like there is a chance for light snow with
little to no accumulation. The one at the end of the period looks to
have a better chance of precipitation...however the are discrepancies
in the models leading to differences in timing.

At the beginning of the period a wave is expected to be exiting
the area and cloud cover looks to be decreasing overnight. While
temperatures may not be that warm on Sunday...we will see sun
nonetheless...making for a pleasant Sunday. A weakening wave is
forecast to advect into the area Monday and lead to some slight
chances of snow Monday. Not impressed at all with this system...think
that overall snowfall will be light and most likely to occur in
western and northern zones. If it does snow...it will likely be of
the nuisance variety.

Behind this system we see our cold temperatures return to the area
again after a warmer December. Monday night and Tuesday night look
to be cold with lows in the single digits and even below 0 on Monday.
Wind chills will be below 0 on Monday night...close to ten below
in northwest zones and then -15 on Tuesday night in northwest zones. After this
the flow begins to moderate and temperatures warm back up to near
normal.

At the end of the period another system is forecast to affect the
Midwest. It is too early to nail down specifics of this storm.
Current forecast suggests that the freezing line will be over the
County Warning Area...meaning we could see a rasn mix with it. This will probably
change as we get closer to the forecast.

As far as temperature forecasts go...long term boi verify stats
suggest that the consraw blend is nailing the temperatures for
highs and low in the 30 to 45 day average. Decided to start with
these temperatures and then adjust them a degree or two from there.

&&

Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1143 PM CST Friday Dec 26 2014

Conditions to deteriorate into MVFR and IFR with areas of LIFR
overnight and Saturday morning in low clouds...fog and areas as
light rain/drizzle as low pressure lifts north and a cold frontal
passage follows. Few flurries or patchy drizzle remain possible
at Cid and dbq Saturday morning. Winds to veer to westerly by
Saturday morning and become gusty at 10-20+ kts. Anticipate gradual
lifting of ceilings to MVFR by Saturday afternoon and lingered through
the rest of taf cycle although partial clearing and improvement to
VFR is possible late in the day into Saturday night.

&&

Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&

$$

Update...05
synopsis...haase
short term...haase
long term...Gibbs
aviation...05

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