Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 041725

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1125 AM CST Sun Dec 4 2016


Issued at 1027 AM CST Sun Dec 4 2016

The mesoscale band of heavy snow has been anchored for 2 to 3
hours over an axis from Washington Iowa through the Quad Cities to
near Sterling Illinois. Amounts are already 4 to 6 inches, with
some elevated surfaces seeing near 7 already. I`m going to go with
a warning immediately for the counties around I-80 east of Johnson
county. I have also expanded the advisory a few counties south to
account for the short term rapid accumulation of snow to the 2 to
4 inch range. In the last hour, some reports of 1/2 mile
visibility and 2-3 inches have been received.

Amounts of 6 to 8 inches should be common by Noon in the Warning


UPDATE Issued at 844 AM CST Sun Dec 4 2016

The slow moving FGEN band of heavy dendritic snow (1/4 mile
visibility) will continue to redevelop over locations along and
north of I-80 this morning. The main band of forcing that models
have been picking up on is making progress through central Iowa.
These two features will keep the moderate to heavy snow going
through noon in eastern Iowa and through mid afternoon in
Illinois. Reports of 3 to 4 inches are already coming in for
locations near I-80 to highway 20, and another 2 to 3 should fall
this morning. Thus, this event may reach warning criteria of over
6 inches along and north of I-80. Impacts are confined to snow
only, and given the lack of wind/ice/refreezing, a high end
advisory still seems like the best fit headline.

Total amounts along and north of I-80 IA/IL are now expected to
be 4 to 6 inches. Lower amounts are expected south with lighter
snow, and warmer temperatures making totals of 1 to 3 more common.


UPDATE Issued at 741 AM CST Sun Dec 4 2016

2 to 3 inches of snow have already fallen across the northern CWA
this morning. Current radar shows a moderate snowfall band
transversing north across the CWA. With accumulations on roads
starting to show up, believe that any other bands today will just
add to the total and any concern about warm ground temps are over,
especially in areas where accumulations on road are occurring.
Have brought up overall totals across the northern CWA, looks like
3 to 5 along highway 20 is a good forecast. To our west, the fgen
band that was forecast has formed and lead to moderate snow. This
band will track east across the highway 30 corridor this am. The
juxtaposition of these two bands will likely be from highway 30
north. Later shifts will need to refine the forecast,

UPDATE Issued at 416 AM CST Sun Dec 4 2016

Per coordination with ILX, added Mercer County to the advisory.
Fgen band may lead to snowfall across this area reaching criteria
later this morning.


Issued at 253 AM CST Sun Dec 4 2016

Early this morning, snow mixed with rain overspread the area as a
H5 wave advected into the central United States. Snowfall amounts
of an inch or so have been reported over central Iowa. At the
surface, wetbulb zero temps have been reaching above freezing
across the southwest, leading to a difficult forecast for snow.
This snowfall forecast is the main concern for the short term


.SHORT TERM...(Today and Tonight)
ISSUED AT 253 AM CST Sun Dec 4 2016

Difficult short term snow event ongoing with low level moisture
entering the southwest CWA, raising wetbulb temps to above
freezing. Much more clear cut snow event along I80 north this
morning. With these two distinct areas, will break the discussion
between these two.

First, the mixed precip region, mainly along and south of Hwy 34
this morning is proving to be a difficult forecast. Trends across
the area suggest that dry air from the east lost the battle with
moisture advection from the SW. Low level T and moisture profiles
suggest a rain snow mix. Accumulation of snow will be particularly
difficult across this area as warm surface temps and temps above
freezing will likely keep any accumulations on grassy surfaces and
elevated areas. One potential caveat to this, is that models do
suggest a strong forcing and good dendritic growth of snow between
12z and 18z as the wave moves through. The shear magnitude of
this rate may lead to an inch or more some areas. Think that this
could lead to slushy roads across the area. That said, this is
probably the most difficult forecast area as temps and wetbulb
temps are slowly but surely making snow accumulation less likely.

Along and north of I80, with the best chance for accumulating snow
along Hwy 20, is the other area. Snow occurring across north
central Iowa will spread across the area today. Reports from this
area suggest that most of the accumulation has occurred on grassy
surfaces. It appears that roads are being affected, however temps
of the ground remain near freezing. As this heads into our CWA, believe
that an area north of a line from Williamsburg to Freeport, is the
best area for road temps and ground temps to fall below freezing this
morning and lead to snow accumulations before a fgen band comes
through between 12z and 18z. Snow on roads will likely be an
issue across this area and the highest snowfall totals, 3 to 5
inches will occur around the hwy 20 corridor. South of the
Williamsburg to Freeport line, expect 2 to 4 inches of snow on
grassy surfaces, mainly due to the fgen band. Some slushy roads
will be a concern across this area.

Will continue the current advisory for today.

Tonight, the snow cover and clear skies will probably lead to
temps in the 20s across the CWA.

.LONG TERM...(Monday through Saturday)
ISSUED AT 253 AM CST Sun Dec 4 2016

Below to well below normal temperatures and mostly dry.

Long Term Forecast Confidence Assessment...fair or average with main
issue is risk of light snow amounts late Wednesday and Thursday due
to passing disturbance passing to the south and east. Verification
tools and trends suggest evidence that some forecast highs and lows
with heart of the cold air may still be a category or so too mild
for later shifts to reconsider.

Monday...minor changes made with increasing clouds and chance late
PM and overnight for some sprinkles and possible flurries for later
shifts to consider adding on top of the slight chance POPS in the
south. Highs should remain upper 30s north with some residual snow
on ground to lower 40s elsewhere. Lows should be in the lower 30s.

Tuesday...Clearing and colder with northwest winds of 10 to 15+ MPH
with colder trend have lowered a couple of degrees with highs lower
30s northwest to upper 30s far southeast.  Some lingering light
mixed POPS in SE in morning kept. Tuesday night...fair and colder on
northwest winds of 10 to 20 MPH.  Lows upper teens northwest to the
middle 20s southeast.

Wednesday and Thursday...minor changes with low POPS in the
southeast of light snow still possible with passing upper
disturbance. Trimmed temperatures a few degrees.  Highs mostly in the
20s Wednesday and upper teens to mid 20s Thursday.  Mins in the
upper single digits to middle teens are suggested.  With a northwest
wind of 15 to 25 MPH with cold wind chills Thursday & Friday AM
still likely to fall to near zero or below zero for several hours.

Friday...Mostly fair and remaining quite cold with light winds as
high pressure moves in.  Highs still in the 20s with mins mostly
still in the teens and possibly upper single digits Friday night.

Saturday and Sunday...unsettled with a chance or likelihood of snow
as passing disturbance moves through.  Trends do suggest some decent
snow totals may occur but still a few days too far out.  Highs
mostly in the mid/upper 20s to around 30F south and lows in the 20s
Sunday AM and mostly teens on Monday AM with colder air arriving.


.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
ISSUED AT 1123 AM CST Sun Dec 4 2016

Moderate to heavy snow will end from west to east early this
afternoon, but the LIFR conditions of low clouds and fog may
continue for a long time after. With widespread wet snow on the
ground, we will possibly be at minimums all night tonight into
Monday morning. Dense fog and low cigs are possible, though not
indicated by models directly yet. I have gone with 1/2sm fog and
low clouds for now, but next issuance may include 1/4sm fog and
vv001 tonight.


IA...Winter Weather Advisory until 3 PM CST this afternoon for Benton-
     Buchanan-Delaware-Des Moines-Dubuque-Iowa-Jackson-Johnson-

     Winter Storm Warning until 3 PM CST this afternoon for Cedar-

IL...Winter Weather Advisory until 3 PM CST this afternoon for Bureau-
     Carroll-Henderson-Jo Daviess-Mercer-Putnam-Stephenson-

     Winter Storm Warning until 3 PM CST this afternoon for Henry IL-
     Rock Island-Whiteside.



LONG TERM...Nichols
AVIATION...Ervin is the U.S. government's official web portal to all federal, state and local government web resources and services.