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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
610 am CST Friday Jan 30 2015

Synopsis...
issued at 252 am CST Friday Jan 30 2015

Synopsis...500 mb flow becomes zonal today into Saturday morning as
a middle-level vorticity maximum approaches Montana and a cut-off low
slides through the southwest U.S. Into northwest Mexico. Moisture advection
ahead of the cut-off low will interact with the northern stream
shortwave to bring widespread precipitation to the area later on Saturday.
Dry conditions are forecast before this time with seasonal temperatures.

&&

Short term...(today and tonight)
issued at 252 am CST Friday Jan 30 2015

Today...the morning should start out with partly to mostly sunny
conditions per significant clearing apparent on the 0845z GOES infrared
(3.9 micron) image. Although...may have an increase in middle-level
cirrus across NE third of the forecast area from the late morning
into the afternoon. 500 mb relative humidity plots show this feature...currently over S
Manitoba/east North Dakota/northwest Minnesota...dropping in from the northwest with
saturation between 70-80%.

1000-500 mb thicknesses of 528-534 dam and 850 mb temperatures of -4 to -6
c will translate into a seasonal late January day across east Iowa/west
Illinois. Forecast highs range from middle 30s SW of Burlington to middle
20s near Dubuque/Freeport. 1036 mb surface high will keep the area dry.

Tonight...SW return flow around the surface high will ensue. Primary
result of this will be increasing middle-level clouds and the
development of steady but light SW winds around 10 kts. Lows will be
warmest over the west in the middle 20s and coolest over the northeast
in the upper teens.

Long term...(saturday through thursday)
issued at 252 am CST Friday Jan 30 2015

Long term forecast confidence assessment...fair to poor or average to
below average with weekend quantitative precipitation forecast/snow totals and impacts on temperatures
beyond day 3 the main issues. Moisture continuity...run to run and boundary
tools and suggest track a bit too far north and amounts mostly a bit
too high. Phasing issue poorly handled as not sampled yet and this would
need to occur for snow totals of 6+ inches and day shift will be able
to confirm as SW and northwest energies will be in the upper air network. If
area receives widespread 4+ inch amounts then temperatures rest of next
week are likely too mild by 5 or more degrees in many periods...especially
lows with light winds and fair skies.

Overview...initialization and verification is fair to poor with Southern
Plains bl moisture overdone by several degrees on surface dewpoints.
Run to run verification supports a 70/30 mix of GFS with Gem-New Hampshire with
hi-res European model (ecmwf) 20-30 percent too high on quantitative precipitation forecast amounts and too far northwest.

Saturday...areas of rain and snow to overspread the region with evaporative
cooling to convert all precipitation to snow with sustained forcing
as column cools. Later shifts may be able to change areas that have
likely to categorical probability of precipitation to just snow due to the evaporative cooling.
Highs of 35 to 40 are depending on precipitation arriving later in the
day.

Saturday night through Sunday night...phasing of SW and northwest energy suggest
periods of light to moderate snow with 12-15 to 1 ratios. Local tools
based on moisture budget that is slightly lower than blended guidance
supports areas of 4 to 6+ inch amounts with risk of 8 inches. Upper
energy and jet analysis suggest southern 1/2 of area currently preferred
to see highest amounts with 2-4 inches north of Highway 30 corridor.
Again the phasing of the energy from the north and south should be
better known today and will pass the decision on any headline to day
shift. At this time...axis of heaviest snows +/- 40 nm either side
of a otm-mus-vys axis. Mins Saturday night should be on warm side
of guidance with nearly steady temperatures on Sunday as north winds
increase to 15 to 25+ miles per hour. Mins Monday am in single digits are dependent
of snow ending by midnight with clearing skies.

Monday through Thursday...generally dry with some light snow late Tuesday
into Wednesday and below normal temperatures. Decent snow pack suggest
later shifts will need to trim temperatures most periods by 2 to 5 degrees.

&&

Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 610 am CST Friday Jan 30 2015

A surface high pressure ridge will slide across the Mississippi Valley
through today. Therefore VFR conditions are expected through this
taf period. Time-height sections do indicate increasing saturation
between 1-2 kft above ground level this afternoon so mentioned scattered clouds in the
tafs...but there is a chance the clouds become more widespread
than scattered. Winds will turn to the SW overnight tonight but remain
near or below 10 kts.

&&

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

$$

Synopsis...uttech
short term...uttech
long term...Nichols
aviation...uttech

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