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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
1136 PM CST Sat Nov 22 2014

Update...
issued at 655 PM CST Sat Nov 22 2014

Temperatures early this evening were holding nearly steady from
the upper 40s north to middle 50s south with dewpoints in the upper
40s to lower 50s. This has so far confined light fog to areas
north of Highway 30. Area radars and surface reports have
precipitation tied more closely to the strong upper level wave
over Texas...reaching east-NE across OK...southern MO into central Illinois.
The nearest precipitation on kdvn radar was a small shower over
the Bloomington Illinois area...moving northeast.

Have updated the forecast to lower probability of precipitation considerably this evening
and downplay the fog as the steady south wind is keeping low
levels mixed with a lack of convergence to focus saturation.
Better low to middle level lift is still prognosticated to overspread the
area well after midnight...and have continued an upglide from
slight chances this evening to likely probability of precipitation toward morning as low
level moisture deepens. This could result in more drizzle vs rain
and will continue to monitor. Also...fog trends are low confidence
and will keep at least patchy wording in all areas. The best
potential for widespread dense fog may hold off until later Sunday
into Sunday night as low level winds back and then the flow
becomes light and convergent over the area with the developing
deformation axis ahead of the approaching surface low.

&&

Synopsis...
issued at 258 PM CST Sat Nov 22 2014

Analysis at 2 PM depicts a developing storm system in Texas to move
northeast across the forecast area tomorrow. This system is verifying
at least as strong and as moist as solutions supporting widespread
moderate to lower end heavy rain event Sunday. Moisture in place over
upper Midwest producing lots of low clouds and fog past 24 plus hours
that will increase again tonight as Texas system approaches.

&&

Short term...(this evening through sunday)
issued at 258 PM CST Sat Nov 22 2014

Short term forecast confidence...average to above average or fair to
good confidence with main issues increase in fog...drizzle and rain
with possibility of isolated embedded thunder biggest question. Widespread
5 to 1.25 inches or rain to fall over a 6 to 12 hour period expected.
Some risk of training of rain any convection could produce higher amounts
over 1.5 inches.

Tonight...cloudy with increasing low clouds and areas of fog that could
become locally dense...mainly after midnight and toward morning. Drizzle
and areas of light rain should increase and become significant areas
after midnight and even likely more toward morning. Lows should be
quite mild with upper 40s to near 50 degrees allowing for any remaining
frozen ground to melt as has happened past 24 hours reducing any water
issues. South winds around 10 miles per hour will also aid in any remaining
melting of frozen ground.

Sunday...large areas of rain to overspread the area between 4 am and
noon from the southwest with areas of fog becoming more widespread by
afternoon with light southeast winds ahead of surface low. Risk of locally
dense fog will need to be reconsidered by later shifts. Local tools
suggest heaviest .4 up to near 1 inch amounts most areas to fall over
3 to 6 plus hour period...mainly middle day to late afternoon...this would
limit any water issues. The remaining .1 to .25 inches to fall over another
1-3 hour window earlier in morning...possibly before daybreak. Lift
(lightning probability) tool suggest middle day embedded thunder may be
possible if system is a bit stronger than current forecast for later
shifts to reconsider.

Long term...(sunday night through saturday)
issued at 258 PM CST Sat Nov 22 2014

The trend of below normal temperatures will continue for the area
with the potential for two snow events.

Low pressure will move through the area Sunday night and into the
Great Lakes. Rain will be widespread across the area Sunday evening
with fog expected ahead of the cold front.

Starting around midnight Sunday night colder air will begin moving
into the area behind the cold front and slowly change the rain to
snow from west to east. By sunrise Monday the precipitation should
be all snow across roughly the western third of the area with the
rain/snow mix encompassing the central third and the Mississippi
Valley. The eastern third should still be all rain.

Winds will be on the increase behind the front Sunday night with
windy conditions across the area at sunrise Monday. Wind gusts
Sunday night may reach 35 miles per hour.

On Monday...the change over to all snow will be completed during the
morning hours with windy conditions continuing. Wind gusts during
the morning hours Monday may be 35 to 40 miles per hour at times.

A secondary upper level disturbance will move through the area
Monday night maintaining the light snow across the northern half of
the area.

As for snow amounts...1 to 2 inches of snow may be possible north of
Highway 30 by sunset Monday. Highway 30 down to a Galesburg to
Ottumwa line...amounts should be one half to one inch. South of a
Galesburg to Ottumwa line a dusting of accumulation is possible.

The snowfall Monday night across the north half should be a dusting
at most.

On Tuesday...dry but chilly conditions will be seen across the area
as Canadian high pressure moves through the Midwest. Temperatures
will average below normal.

Tuesday night on...
Tuesday night through Thursday the model consensus has slight chance
to chance probability of precipitation for a clipper type system prognosticated to move through the
Midwest. Timing on this event will be critical but current
information suggests a snow event for the area. Storm
track...moisture availability...and temperatures will be very
important regarding potential snowfall amounts but it appears that
some accumulation is possible.

Thursday night through Friday night dry and cold conditions are
expected as another Canadian high moves through the Midwest.
Temperatures should average below normal.

On Saturday mainly dry conditions are expected for the area. There
are indications of a weak upper level disturbance moving through in
the flow aloft that could produce some snow if sufficient moisture
is available. Temperatures will continue to average below normal.

&&

Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1134 PM CST Sat Nov 22 2014

The potential for fog and drizzle tonight has diminished
considerably and the transition to prevailing IFR conditions has
been delayed in the latest forecasts. Ceilings will likely become IFR
before sunrise...with visibilities lowering to an MVFR range. As a
developing storm system approaches from the plains...rain and fog will
overspread the terminals in the morning and continue through the
day with prevailing IFR conditions and periods of IFR or even LIFR
from late afternoon toward evening as the potential for dense fog
increases. A late evening frontal passage will likely bring a
shift in winds from south to west or northwest...followed by
precipitation changing from rain...or a rain/snow mix...to all
snow...just beyond the range of the current forecasts late Sunday
night.

&&

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

$$

Update...sheets
synopsis...Nichols
short term...Nichols
long term...08
aviation...sheets

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