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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
803 PM CST Thursday Feb 11 2016

issued at 803 PM CST Thursday Feb 11 2016

Narrow band of mostly light snow has set up from just SW of dmx
southeast through Centerville and Ottumwa S-southeast to near Quincy Illinois as seen
on area radars. In the dvn forecast area...snow had begun over
the past hour in Fairfield with upstream visibilities around 2 1/2
to 3sm in adjacent S central Iowa . The latest hrrr...rap and NAM
high res models keep this axis of light snow...confined to southeast
Iowa...NE MO into west central Illinois...mainly north of Highway 34. This is
the axis of main upper level forcing...which is nudged up against
a deep dry airmass to the northeast. Surface dewpoints over
eastern Iowa and points east and north were only in the single
digits...and the kdvn 00z/12 sounding indicated a deep dry layer
below 700 mb.

This will likely keep measurable snow limited to southeast Iowa...far northwest MO
and west central Illinois over the next several hours and have backed down
on snow amounts over the central and north for overnight to trace
amounts at best. Will have to watch a weak area of lift the northwest
flow aloft producing light snow in the msp area for much later
tonight as it progresses toward far eastern Iowa and northwest Illinois. Will
handle this with very low probability of precipitation and keep a mention of at least
flurries in all areas through the overnight.


issued at 327 PM CST Thursday Feb 11 2016

High pressure centered over the eastern County Warning Area this afternoon as
leading to clear skies and dry weather for most of the area. A
fast moving clipper is forecast to affect the area later today and
tonight and will be the main forecast concern in the short term


Short term...(this evening through friday)
issued at 327 PM CST Thursday Feb 11 2016

Main forecast concern for the short term are the chances for snow
associated with a fast clipper across the area today. Dry air in
place with the high overhead will limit overall snowfall totals to
around an inch...with locally higher amounts just over an inch.
Hires guidance is in good agreement that this will start near 00z
and be out of the area by 08z.

Guidance today held strong with the consensus on timing and
strongest forcing will remain across our far southern zones. Westward
has around an inch of snow for this area and our forecast
represents this. Latest runs of the hrrr suggests that the best
snow will be out of the area by 06z with lingering flurries
through 09z across the far southern County Warning Area. Winds will remain light
so little to no impacts are expected from this snow. Any snow that
accumulates should be done by the early hours.

Friday will be quiet and slightly warmer..with clearing skies.

Long term...(friday night through thursday)
issued at 327 PM CST Thursday Feb 11 2016

Friday night...latest suite of 12z run models suggest 1045 mb Arctic
high pressure still on track to surge down the upper to middle MS
River Valley Friday night into Sat with a scouring effect. This
feature to cold dump low level temperatures/thickness values to produce sub-
zero lows across most of the County Warning Area...but some concern that ongoing
mixing surface winds in incoming high pressure gradient to limit a
complete bottom out. But due to brute force cold air
advection...will still go with lows from 5 to near 10 below zero
across the northwestern third of the County Warning Area...0 to 5 below along and
north of i80...and to the low single digits above zero in the
southern County Warning Area. Surface winds decreasing to 7-10 miles per hour toward sunrise Sat
still to produce advisory level wind chills across at least the
northwestern third of the dvn County Warning Area...and possibly along the Highway 20
corridor in northwest Illinois.

Saturday and Sunday...the Arctic high overhead will make for
temporary clear and calm/light wind conditions for first part of the
day Sat...with high clouds on the increase as the afternoon
progresses. This ahead of the organizing short wave upper trough that
will look to propagate toward the southwestern Great Lakes and middle MS
River Valley on Sunday in broadening west-northwesterly steering
flow. The various medium range solutions suggest some type of
associated warm air advection Wing of snow will look to try to get
into the western or southwestern County Warning Area by early Sat evening...but
feel models may be too quick with this taking into account
strength of dry surface ridge axis still on the move over and east of
the County Warning Area at that time. But by midnight Sat night...both the 12z run
European model (ecmwf) and Gem suggest some light snow accums starting to take
place already in the far southwestern County Warning Area. Again siding with the
12z Gem/European model (ecmwf) which are in decent agreement...the warm air advection Wing of snow
ahead of the main upper trough will look to continue to spread
eastward across much of the western 2/3s of the County Warning Area through 12z
Sunday...but may get eroded some as it does by ongoing dry air in
place and also some impact of much of the initial lift going into
the top-down saturation process. The latest Gem may have the best
handle on this idea with just a dusting to half inch west of the
MS river by 12z Sunday...but will go with a few tenths to near an
inch southwest of a line from the quadrant cities...and to
Macomb in western Illinois.

Then the main snow event with the upper trough will look to occur on
Sunday and will continue to adjust probability of precipitation up into likely or even
categorical. But the 12z run American models/especially the 12z GFS/
which hint at high end advisory or even low end warning criteria
amount snows by Sunday evening combining the two snow making
processes...seem too wet...too strong looking at middle and upper level
jet dynamics more favorable to the south...and their deep saturation
in the dendritic growth zone for much of Sunday morning into early
afternoon. So currently favor a blend of the 12z Gem/European model (ecmwf) moisture
and forcing profiles which suggest most of the County Warning Area to get 1-3 or 2-4
inches of snow by Sunday evening. Increasing south winds of 15-20
miles per hour may produce some drifting trouble by Sunday afternoon as there may be a need for an eventual advisory even with the
lighter amounts produced by these favored solutions. Still 1-3 more
model runs needed to further define this snow event for more

Monday through next the passing trough continues to evolve
along and east of the region early next week..resultant major storm
should take off well to the east/southeast of local area of concern.
But there may be some nuisance light snow at times across the area in
the wake of the main system...or even a secondary weak clipper late
Monday into Tuesday. Longer range indications then suggest the clipper
inducing northwesterlies will eventually give way to milder upper
ridging by middle to late next week...but the trend has been to delay
it/S arrival especially if re-enforcing troffiness establishes across
the western Great Lakes Tuesday into Wednesday like some of the latest ensembles
suggest. ..12..


Aviation...(for the 00z tafs through 00z Friday evening)
issued at 538 PM CST Thursday Feb 11 2016

A fast moving upper level system will spread light snow across
central and southeast Iowa this evening. The greatest impact will
be at brl...where a period of IFR conditions is likely this
evening...primarily due to low visibilities. Further north...Cid
and mli will likely remain on the edge of this system and the
latest forecast has a period of MVFR conditions this
evening...followed by MVFR ceilings and flurries through the rest of
the night. Have also included flurries at dbq...with ceilings lowering
to MVFR late tonight through Friday morning. A cold front dropping
south through the area Friday will be followed by gusty northwest
winds as high as 20 to 30 kts in the afternoon.


Dvn watches/warnings/advisories...


short term...Gibbs
long term...12

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