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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
732 PM CST Sat Dec 20 2014

Update...
issued at 725 PM CST Sat Dec 20 2014

Latest observation...Road reports...and spotter reports indicating some
slick conditions developing this evening north of Interstate 80...due
to freezing drizzle and some fog freezing on roadways. Bridges and
less traveled roadways are especially prone to light icing. The
main impacts through early evening are located from Tipton and
Cedar Rapids...north to Anamosa and Manchester. Road surface
temperatures are hovering near freezing. With continued moisture
advection overnight...not overly confident in prolonged icing
across the north. So for now...have issued a Special Weather
Statement for areas north of I-80. Will monitor trends for
possible Freezing Rain Advisory.

&&

Synopsis...
issued at 234 PM CST Sat Dec 20 2014

Analysis at 2 PM CST shows all of upper Midwest under low clouds and
isolated areas of light fog and a few flurries as weak south flow
bringing moisture in from the South. Strong digging jet entering Pacific
with developing Lee side trough to keep area moist and relatively mild
next 24 hours before rain arrives late Sunday into Monday. Energy upstream
supports deep trough by middle of next week to our east with
colder temperatures.

&&

Short term...(this evening through sunday)
issued at 234 PM CST Sat Dec 20 2014

Short term forecast confidence...good or above average...main issue
is coverage of light drizzle and possibly freezing drizzle tonight
north of I-80. Patchy light fog with 1-2 miles visibility may also
occur. Area low and high temperatures should be with a degree or
two of forecast. Areas of drizzle may continue well through Sunday
as temperatures rise well above freezing.

Tonight...isolated very light flurries should end next few hours with
patchy light drizzle and possibly light freezing drizzle north of I-80
by late evening and into overnight hours. Any freezing drizzle that
does occur north of I-80 besides trace amounts will have temperatures
around 32 degrees supporting limited...if any impacts with proper
precautions. Lows should be 29 to 34 degrees with slowly rising
temperatures overnight as south winds increase to 5 to 10 miles per hour with
area visibilities mostly between 2 and 5 miles.

Sunday...south winds of 5 to 15 miles per hour to allow for area highs of 38 to
45+ degrees with patchy drizzle...changing to a chance of light rain
by middle to late afternoon with amounts generally less than a few hundredths
of an inch. Light fog still possible with visibilities mainly 2 to
5 miles. Damp conditions for outside activities.

Long term...(sunday night through saturday)
issued at 234 PM CST Sat Dec 20 2014

The weather pattern will become more active and will be undergoing a
change during the week. When this occurs...predictability on how
individual systems will evolve is much lower.

The next system will affect the area Sunday night into Monday. Until
the atmosphere saturates to a sufficient depth and forcing
increases...drizzle with some light rain will be seen across the
northwest half of the area Sunday evening. After midnight the
drizzle will slowly turn over to all rain. The far eastern parts of
the area should remain dry Sunday night.

On Monday deeper moisture and stronger forcing will move across the
area. A continued warming of the atmosphere from southerly winds
means the precipitation will be in the form of all rain. Maximum
temperatures are expected to average above normal.

Monday night/Tuesday the storm system will move into Wisconsin and
Michigan. Rain across the area Monday evening will become more
spotty as the forcing decreases. Slightly colder air being pulled
down from the northern plains suggests the potential for a rain/snow
mix over the northwest half of the area late Monday night...and
possibly west of a Dubuque to Ottumwa line on Tuesday. If the drying
aloft that is suggested by the models occurs...the potential exists
for any precipitation to be in the form of drizzle or exceedingly
light snow. If any snow does occur...any accumulations would be a
dusting at best.

Tuesday night on...
attention then turns to the much advertised storm system for middle
week.

The current model consensus has slight chance to chance probability of precipitation Tuesday
night/Wednesday and slight chance probability of precipitation over the eastern half of the
area on Wednesday. The precipitation type would be in the form of
snow.

The overall big picture indicates considerable energy aloft moving
in from the Pacific northwest to help develop this storm system.
Trends with the models are suggesting that this storm system may
track further to the south and east. Again...this system will need
to be watched carefully as the eventual track will dictate snow
amounts. Regardless...there will be some degree of impact on
Holiday travel.

The model consensus has dry conditions on Thursday as high pressure
quickly moves through the Midwest. Temperatures should be close to
normal.

The model consensus has slight chance to chance probability of precipitation Thursday
night...chance probability of precipitation Friday...and slight chance probability of precipitation Friday night for
yet another storm system. There is considerable disagreement among
the models on where this storm will track so it too will need to be
watched carefully. Where this storm system eventually tracks will
dictate the potential for any snow accumulation.

On Saturday...the model consensus has dry conditions as yet another
high pressure moves through the Midwest. Temperatures should average
below normal.

&&

Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 603 PM CST Sat Dec 20 2014

A warm front will lift north through the area overnight. Expect
periods of drizzle or freezing drizzle depending on surface
temperatures...and a stray flurry at times. With increasing low level
moisture and dewpoints...the threat for prolonged fzdz will likely
be confined to the far north in vicinity of kdbq. Kmli/kcid may be cold
enough for periods of fzdz this evening...but should warm above
freezing overnight. IFR/LIFR conditions will dominate
overnight...with some improvement to MVFR expected by middle to late
Sunday morning.

&&

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

$$

Update...rp Kinney
synopsis...Nichols
short term...Nichols
long term...08
aviation...rp Kinney

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