Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 101244
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
644 AM CST Wed Jan 10 2018

.UPDATE...
Issued at 636 AM CST Wed Jan 10 2018

Sometimes a synoptic set up of moist warm advection over snow and
cold ground left over from an arctic outbreak don`t do what
Meteorology 101 tells you. Well, maybe mostly what you`d expect in
that we do have widespread fog and low clouds, but the
visibilities have never really become widespread below 1/2 mile,
and we`ve coordinated a change to cancel the advisory with St
Louis and Lincoln`s offices. A couple things that seem to be
inhibiting the fog`s density are wind remaining fairly strong up
around 10 to 15 kts gusting to 20, and very widespread stratus
bases of 2 to 4 feet. That`s likely the reason we`ve mainly seen
the lower visibilities occurring at higher elevation sites, like
DBQ. In the end, there`s still a risk of dense fog, over the
entire area, but we can`t just stay the course saying it`s out
there, when it isn`t. We`ll monitor things close, and if meso
models are right, we might drop visibilities a bit again toward
mid morning, but will wait until that trend verifies. Those same
models said our entire area would be down under 1/4 all night.

ERVIN

&&

.SYNOPSIS...
Issued at 330 AM CST Wed Jan 10 2018

Shallow moisture continues to pump up northward over the area, with
low clouds, widespread 3/4 to 2 mile fog, and patchy dense fog,
which through 2 AM has been confined to higher elevation sites like
the Dubuque Airport. We have closely monitored web cams, and road
conditions and find ourselves in a bit of a hole as far as hazards,
which seem more prevalent to the north and east. The trend in all
part of the CWA since 1 AM, is IMPROVEMENT. That, plus road and wet
bulb temperatures rising above 32 suggests strongly that new
headlines should not be issued for our counties.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CST Wed Jan 10 2018

There is a dense fog advisory out in the southern counties, and
dense fog has yet to become widespread beyond a a single ob here and
there. With this headline already out, and a chance dense fog could
form as higher dewpoints arrive, we`ll leave it in there for now,
but if it does not form soon, or improvement above 2 miles occurs
soon, we will cancel it.

The rest of the CWA will continue to see low stratus clouds today,
and some fog, which could be dense, as that`s what models are
consistently saying, but is not locally happening on a widespread
basis. The temperatures will rise today, based largely on moisture
advection at low levels. All guidance brings mid to upper 40
dewpoints into the area tonight, on south winds. This air is
generally found over Missouri with lower 40s dewpoints, and through
additional advection ahead of the intense cold front, we should
bodily force temperatures upward with nearly all surface snow and
ice gone by tonight.

Rain chance tonight continue to be plagued with the interaction with
the dry slot arriving about the same time as the forcing for
rainfall. This may result in a period of drizzle near the front, and
little else. That drizzle may be widespread enough for pops to
remain high, and that leaves this forecast generally unchanged with
chance to likely pops for light rain and drizzle. I will leave
mention of fog in over the current deeper snow pack(north 1/2)
through tonight, but this threat seems to be decreasing now.

ERVIN

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 330 AM CST Wed Jan 10 2018

Thursday

A strong cold front with a rapid temperature drop of 20 degrees in 3
hours is expected to move from west to east through the CWA! Most
locations will fall from the 40s to the 20s in that time. Also, NW
winds will be gusting around 30 mph.

The front will reach the western CWA during the mid morning hours,
should be near the Mississippi River around midday and reach the
far east by the mid afternoon. Temperatures will continue to
plunge through the evening and overnight, bottoming out in the
single digits west of the Mississippi River and teens elsewhere -
for a less than 24 hour drop of 30-40 degrees.

Flash Freeze Potential:

Areas of light rain and fog are likely ahead of the front Thursday
morning. Moisture and lift behind the front are limited. However,
there is a chance for a brief period of sleet, possibly snow
across the far NW, before the precip completely ends. The threat
for freezing rain is low.

One concern is for moisture from the rain that falls during the
morning, freezing during the afternoon. This is low confidence
because a lot of the water on roads may evaporate before it has a
chance to freeze. The less time there is between rain falling and
temps crashing into the 20s, the better chance for ice to form on
roads - with untreated roads most susceptible. Of course any
puddles or areas of standing water from the snowmelt will freeze
and create icy spots on sidewalks, driveways, and parking lots.

Friday and Saturday

All models have dry conditions with secondary vort. max staying
well to our east. Main story is a return to below normal temps. A
1045 to 1050mb high is forecast to build into Dakotas leading to
cold northerly winds locally. Highs are forecast in the 20s/10s
and lows in the single digits above and below zero by Saturday
night. We could be close to wind chill criteria of -20 F in the NW
late Friday night into Saturday morning.

Sunday On

Models in good agreement tracking a slow moving clipper and deep
upper trough through the Midwest and Great Lakes. Right now, looks
like a period of light snow for E Iowa/NW ILlinois Sunday PM into
Monday. Still plenty of time for the details to change. Well
below normal temps may require wind chill headlines into early
next week. Uttech

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday Morning)
ISSUED AT 524 AM CST Wed Jan 10 2018

Low cigs will dominate the weather today at all sites, as warm
moist air rides up over the cold ground. Fog, possibly dense at
times below 1/2 mile, will be possible as well, but has not been
occurring in the past 6 hours much. Thus, visibility of 1/2 to 2
miles will be prevailing through mid morning, where a slow trend
toward IFR then late afternoon MVFR cigs. Visibilities this
afternoon and tonight are expected to be generally good, but will
need to be watched if any fog can form in the mild air.

ERVIN


&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

UPDATE...Ervin
SYNOPSIS...Ervin
SHORT TERM...Ervin
LONG TERM...Uttech
AVIATION...Ervin



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