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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
1206 PM CST sun Feb 1 2015

issued at 728 am CST sun Feb 1 2015

Increased snow totals slightly for the central and east-central
section of the forecast area. Thinking an additional 2-4 inches of
snow will fall between 12 PM and 6 PM today in this area as the
850 mb deformation zone pivots and only slowly weakens into the
evening. Therefore...the Winter Storm Warning has been updated
with storm totals of 12-15 inches along the I-80 and Highway 30
corridors. The highest totals will most likely occur over the
eastern portion of this zone. As of 6-7 am...have received
numerous reports between 7-9 inches across east-central/NE Iowa and
parts of northwest Illinois.


issued at 229 am CST sun Feb 1 2015

Synopsis...Winter Storm Warning remains in effect until 9 PM tonight
for widespread snow and blowing snow. Total accumulations between 7
to 12 inches are forecast. Extrapolation of snowfall reports
received between 12am-1am puts most areas in the 3-5 inch range as
of 4 am so we are not quite halfway through the storm.

Snow consistency has been very wet thus far averaging near 10:1
resulting in very slippery roadways. However...slrs will increase
through this morning as the snow slowly transitions to a drier

Biggest change in the forecast is the swath for snow amounts of 8+
inches has expanded in areal coverage...encompassing most of the
County Warning Area. The highest totals approaching 10-12 inches will be found
through the central/east-central section of the forecast area.

Additional accumulations of 4 to 8 inches are forecast between 6 am
today to 12 am tonight.


Short term...(today and tonight)
issued at 229 am CST sun Feb 1 2015

Today through tonight...the 850 mb low will take a favored track for
significant snowfall to occur going from southeast Nebraska to east-central
Illinois by 6 PM...remaining just south of the dvn County Warning Area. 850 mb moisture
convergence shows a nice deformation band pivoting and maintaining
itself across the dvn County Warning Area through this afternoon.

Time-height sections display deep Omega intersecting the dendritic
growth zone within a highly saturated environment from the surface up to
300 mb. Heaviest snow will fall through 12 PM today. Area of 0-1 km
convergence/925-850 mb frontogenesis will coincide with deep ascent
via upper divergence in right entrance region of a 300 mb jet
streak. Moist adiabatic lapse rates in the 900-750 mb layer will
develop above the area of low-level forcing leading to the potential
for some mesoscale convective banding. Given this scenario expect a
period of snowfall rates near 1-1.5 inches per hour. One of these
bands moved through the quadrant cities between 200-330 am.

As 500 mb vorticity. Maximum crosses east Iowa/west Illinois during the afternoon...a
period of DCVA and weak middle-level frontogenesis will continue light
snow through the evening.

Impacts...although snow intensity will decrease into the
aftn/evening...NE winds will increase and gust between 30-40 miles per hour
which will create very dangerous travel conditions...especially in
rural areas. Occasional near whiteout conditions will be possible
but since the snow intensity will be lighter do not expect
sustained periods of visibilities at or below 1/4 of a mile.
Definitely a situation to monitor.

Slrs will transition to near 15:1 on average through the morning hours
and into the afternoon. Average dgz depths between 100-150 mb and falling
thicknesses support the higher ratios. This more powdery snow will
be easily blown around as the strong pressure gradient on the northwest
side of the surface low moves through and cold air advection results in good bl mixing.

The snowfall should come to an end between 9 PM-12 am and winds
should gradually subside after this time as well. Lows will fall
into the single digits above and below zero and steady northwest winds will
create wind chills between -5 to -15 f.

Long term...(monday through saturday)
issued at 229 am CST sun Feb 1 2015

Major winter storm ending this evening...then seasonably cold to
very cold and mostly dry.

Long term forecast assessment confidence...good or above average
with limited sensible weather issues. Mostly dry to dry conditions
with significant fresh snow pack impacts on temperatures the next
several days the main issue after passage of storm today.

Overview...straight forward initialization and verification with
little sensible weather issues beyond tonight. Trends and run to
run variance supports a 75/25 mix of GFS with hi-res ECMWF/Gem-NH.
This supports trend toward colder temperatures for later shifts in
some periods...likely impacted by deep and fresh snow cover.

Monday...fair and cold with light winds. Trimmed high temperatures
a degree or two most locations due to fresh snow pack. Most areas
highs may still be a few degrees too high for later shifts to consider.

Monday night through Tuesday night...variable clouds with chance of
light snow with passing weak upper disturbances. Any snow amounts
should be mostly an inch or less due to limited moisture and forcing.
Mins may need trimming if clouds arrival delayed Monday night. Again
temperatures Tuesday may still be a bit too mild most locations.

Wednesday through Saturday...mostly fair and cold with next Arctic
front that may produce light snow south sections on Wednesday. Local
tools with deep snow pack suggest temperatures likely at least 1 to
2 categories too high. Potential for negative middle/hi teens for lows
Thursday morning with wind chills near -20 to -25 degrees for several
hours for later shifts to consider.


Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 1148 am CST sun Feb 1 2015

IFR to LIFR conditions in snow and blowing snow will persist into
this evening along with gusty northeast winds 15-30 kts. Expect
improving conditions to VFR with diminishing north to northwest
winds at or below 10 kts overnight into early Monday morning as the
storm system pulls away.


Dvn watches/warnings/advisories...
Iowa...Winter Storm Warning until 9 PM CST this evening for Benton-
Buchanan-Cedar-Clinton-Delaware-Des Moines-Dubuque-Henry Iowa-
Muscatine-Scott-Van Buren-Washington.

Illinois...Winter Storm Warning until 9 PM CST this evening for Bureau-
Carroll-Hancock-Henderson-Henry Illinois-Jo Daviess-McDonough-
Mercer-Putnam-Rock Island-Stephenson-Warren-Whiteside.

MO...Winter Storm Warning until 9 PM CST this evening for Clark-



short term...uttech
long term...Nichols

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