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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
858 PM CST Sat Jan 31 2015

Update...
issued at 857 PM CST Sat Jan 31 2015

Forecast remains essentially on track and the recently sent west-southwest
product has only minor wording tweaks. Snowfall amounts were
unchanged.

At 8 PM...the cold front has settled into the Highway 20 corridor...
where east-NE winds were advecting colder air with dewpoints in the
upper 20s...helping the precipitation make a solid transition to
snow. Further south...I-80 appears to be a rough dividing line
for a rain and snow mix north to mainly rain south. The kdvn
sounding showed the freezing level at 00z roughly around 900 feet.
Upstream over northern MO into south central Iowa...dynamic cooling
from stronger forcing spreading in from SW has changed the
precipitation primarily over to all snow...which has likely
reached into Scotland County MO and Van Buren Colorado Iowa. This
transition will continue to spread northeast and at the current rate...
the remaining areas of rain...or mixed precipitation should
change over to all snow by 10 or 11 PM.

Snow has begun to accumulate at the National Weather Service office over the past
hour...with just over a half inch measured at 845 PM. This
suggests that most areas should begin to accumulate within an hour
after the transition and likely reach or exceed the 1 inch mark
before midnight.

&&

Synopsis...
issued at 356 PM CST Sat Jan 31 2015

Winter storm with significant snowfall accums for the area still on
track next 24+ hours... as energy ejecting from southern stream
closed low over the southwest phases with digging northern stream
trough. Combination of the strong forcing and anomalously high
moisture (pacific and Gulf origins) being entrained into system
with precipitable waters 3-4 sigma or Standard deviations above normal support
lend support for the significant snow accums.

&&

Short term...(this evening through sunday)
issued at 356 PM CST Sat Jan 31 2015

Confidence is high on widespread significant snowfall accums with
north 1/2 of County Warning Area favored for the heaviest amounts. Confidence
though remains moderate on exact amounts.

Timing...rain/drizzle continue into early this evening before
changing over to snow from north to south... with some areas far
south possibly waiting until after midnight to change.

Snowfall and amounts...snow moderate to locally heavy at times
overnight through Sunday am with visibilities below 1 mile in
the heavier snow. Character of snow to change with initially tonight
mainly a wet snow then turning more powdery on Sunday with arrival
of colder air. Track of surface low just south of County Warning Area with 850/700 low
tracks across the southern County Warning Area is favorable for heaviest snow
accums over roughly the northern 1/2 or so of County Warning Area where strength
and duration of moisture and forcing support 6-11 inches. Across
the southern County Warning Area still expect significant accums of 6 inches or
more (especially near Highway 34) with potential for decent gradient
or cutoff in amounts far southern County Warning Area. Snow should begin to taper
off in intensity Sunday afternoon.

Winds...light winds this evening to turn more easterly overnight
at 5-10 miles per hour. On Sunday winds will increase from northeast at
15-30 miles per hour which with more powdery nature of snow may make for some
drifting and patchy to areas of blowing snow making snow removal
challenging. Visibilities could also lower below 1 mile at times.

Temperatures... dropping into the 20s to around 30 tonight. Steady early on
then falling into the lower 20s and teens in the afternoon.

Wind chills..dropping into the single digits above and below zero
Sunday afternoon.

Long term...(sunday night through saturday)
issued at 356 PM CST Sat Jan 31 2015

Forecast focus on below normal temperatures during this extended
along with a couple of clippers potentially bringing light snow
accumulations.

Sunday night...deformation zone will continue to produce snow over
the County Warning Area during the evening. Additional accumulations will be up to
2 inches. The cyclone will be moving into southern Ohio with a tight
gradient still over the County Warning Area during the evening...with north winds
continuing to gust to 30 to 35 miles per hour. Considerable drifting and some
blowing snow due to the dry fluffy nature of the falling snow. After
midnight...the cyclone tracks farther away and high pressure begins
to build into the area. The snow will be ending and winds will be
diminishing. Strong subsidence and colder/drier air will allow
clouds to decrease overnight. This combined with deep snow cover
should drop minimum temperatures into the single digits below and
single digits above zero.

Monday through Saturday...a cold week with below normal temperatures
basically remaining below freezing. The coldest days will be on
Monday and Thursday with highs only in the teens. The coldest night
is expected to be Wednesday night where minimum temperatures drop to
zero to 8 below over roughly our northern half...along with wind
chills of 15 to 20 below zero. Our southern half should see lows in
the single digits above zero.

There looks to be a couple of opportunities for Alberta clippers
bringing some light snow to portions of the County Warning Area. However...confidence
is low in regards to timing/intensity and track of these systems.

&&

Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 600 PM CST Sat Jan 31 2015

Winter storm to bring deteriorating conditions to the entire area
tonight...continuing through Sunday. Widespread rain and drizzle
early this evening will transition to all snow by midnight.
Visibilities and ceilings will be mainly IFR early in the
evening...lowering to low IFR and very low IFR as the snow lowers
visibilities...while ceilings and vertical visibilities lower to a few
hundred feet. Sunday...as the storm center passes to the
south...winds will ramp up to 15 to 25 miles per hour from the northeast with
even higher gusts during the afternoon. Continued snowfall...along
with blowing and drifting will keep visibilities likely below IFR
and likely vlifr through the afternoon. Forecast snowfall totals for
the region is in the range of 8 to 11 inches. Heavy snowfall
rates followed by drifting snow Sunday may create challenging
conditions for Airport ground operations.



&&

Dvn watches/warnings/advisories...
Iowa...Winter Storm Warning until 9 PM CST Sunday for Benton-Buchanan-
Cedar-Clinton-Delaware-Dubuque-Henry Iowa-Iowa-Jackson-
Jefferson-Johnson-Jones-Keokuk-Linn-Louisa-Muscatine-Scott-
Van Buren-Washington.

Winter Storm Warning until 9 PM CST Sunday for Des Moines-Lee.

Illinois...Winter Storm Warning until 9 PM CST Sunday for Bureau-Carroll-
Henry Illinois-Jo Daviess-Mercer-Putnam-Rock Island-Stephenson-
Whiteside.

Winter Storm Warning until 9 PM CST Sunday for Hancock-Henderson-
McDonough-Warren.

MO...Winter Storm Warning until 9 PM CST Sunday for Scotland.

Winter Storm Warning until 9 PM CST Sunday for Clark.

&&

$$

Update...sheets
synopsis...05
short term...05
long term...haase
aviation...sheets

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