Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 190000
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
600 PM CST Wed Jan 18 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 330 PM CST Wed Jan 18 2017

18Z surface data has high pressure over the Ohio and Tennessee
Valleys with an area of low pressure from eastern Wyoming into
eastern Colorado. Dew points were in the 20s across the northern
Plains with 30s from the Great Lakes and Ohio Valley into the
central Plains. Dew points of 40 and higher ran from the Tennessee
Valley and southern Plains to the Gulf Coast.

&&

.SHORT TERM...(This Evening through Thursday)
ISSUED AT 330 PM CST Wed Jan 18 2017

Mainly quiet conditions will be seen across the area late this
afternoon and tonight. High moisture levels in the lower atmosphere,
a warm layer aloft, breaks in the clouds, and decreasing winds
should allow patchy fog to develop starting around mid-evening and
continuing through sunrise Thursday.

Fog trends tonight will need to be watched. Fog was only patchy last
night and that should be the case tonight. However, if a large
enough area of clear skies develop tonight then the fog may become
much more widespread.

Any fog that develops tonight will slowly lift Thursday morning.
Moisture aloft moving into the area combined with an approaching
upper level disturbance will allow rain to slowly break out across
the south half by late Thursday morning and overspread the area
Thursday afternoon.

If trends with the models are correct, a layer of unstable air aloft
will develop Thursday afternoon. If forcing becomes strong enough
then a few isolated thunderstorms are possible.

Temperatures tonight and Thursday will continue to average above
normal.   ..08..

.LONG TERM...(Thursday Night through next Wednesday)
ISSUED AT 330 PM CST Wed Jan 18 2017

Thursday night...As closed upper low pivots up acrs IA Thu night, it
will continue to spiral up a moisture feed and back-wrap it westward
acrs the area, fueling ongoing bands of rain. Some signs of in-
wrapping drier mid layer from the southwest into a convergence
ribbon of adequate mid layer lapse rates/MUCAPES for at least some
embedded thunder Thu evening...with the southeastern third to half
of the DVN fcst area more favored. For now will go isolated in the
southeastern third of the CWA. Low temps Thu night may not be all
that much cooler than Thu afternoon and will fcst mid to upper 30s.
Extent of lift and saturation using a 12z GFS/ECMWF blend suggest
additional rainfall amounts of just a few hundredths in the far
southwestern CWA, to 3 to 4 tenths in the far east/ northeast by Fri
morning...making for event totals generally from around 0.15 of an
inch in the far west, to 4-5 tenths of an inch in the east.
Localized higher swaths possible under thunderstorm paths. These
kind of amounts for the time frame hopefully will only translate to
minor additional impacts on area rivers. For now will through out
the 12z NAM with it`s 0.70 to 0.80+ inch PWAT`s and produces
rainfall amounts similar to those values acrs the east half of the
CWA, which would be a bigger impact to any ongoing hydro-related
situations. Where the rain wanes late Thu night, areas of fog and
drizzle could take over.

Friday... The initial wave lifts north into MN/WI by Fri afternoon,
taking organized rain with it. May still have lingering areas of fog
and drizzle well into the day. Am a bit leery of going too mild on
Fri, but will go with low to mid 40s for much of the area despite
cloud cover hanging on. Both the 12z ECMWF and GFS in good agreement
of then suggesting the next upper level trof/wave to sweep acrs the
area Fri night embedded in cyclonic southwesterly steering flow. But
fcst soundings suggest enough of an ongoing dry mid layer above H85
MB that any precip getting wrung out may be more in the way of
drizzle as opposed to rain. Fog may continue to be an issue as well
into Fri night. Seasonably mild lows in the upper 30s to lower 40s
into Sat morning limiting any freezing threat.

Saturday through Monday...The strongest warm draw of the weekend
still looks on tap for Sat with most guidance highs from the upper
40s, to well up in the 50s. Any type of cloud cover break for a
period Sat morning into afternoon may even allow for a 60 degree
occurrence somewhere. Then the focus turns to the next main southern
stream wave rolling out of base of Rex block and acrs the central
into eastern CONUS Sunday into Monday. The latest run medium range
models continue to trend south with this vortex, so much now that
any real measurable rainfall on this system`s northern flank now
occurs well to the south of the DVN CWA. Temps to trend down into
early next week but still well above normal for this time of year.

Next Tuesday and Wednesday...Will have to watch for yet another
cyclone rolling out to the east-northeast out of lingering
southwestern CONUS troffiness, but the medium range models are
varying greatly on how far north or south this feature propagates
out acrs the midwest.  ..12..

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
ISSUED AT 556 PM CST Wed Jan 18 2017

Low level moisture on south winds will return bringing IFR/LIFR
conditions to all the terminals by late this evening and early
overnight. These conditions will continue on Thursday with light
rain developing in the afternoon as south winds of 5 to 15 MPH
continue.

&&

.HYDROLOGY...
Issued at 330 PM CST Wed Jan 18 2017

Rock River: Flow routed from upstream as well as ongoing ice action
may still produce sudden spikes above flood stage at Como, thus a
flood warning has been re-issued for that site. Flood warnings for
moderate flooding continue at Joslin and Moline. At Moline, there is
still some uncertainty in routed water flow toward this site from
the Green River, and there is some concern that this location may
rise above the Major flood stage. Also, ice movement in the river
may cause rapid fluctuations in the stage at this location.

Mississippi River: The latest river stage trends indicate that river
levels continue to rise at both sites(Gladstone and Burlington) that
are in moderate flood. Increased flow from runoff from recent
rainfall, and the ongoing ice jam downstream of Burlington will
likely lead to continued rises on the Mississippi in these areas as
well as possibly a bit further upstream. Water backing up further
upstream is producing sudden jumps at New Boston and Keithsburg.
Once the ice jam erodes and eventually frees, expect the levels in
the river around the sites in flood to drop noticeably.

Other sites: Recent rainfall/run-off combined with ice action is
also producing rises to or near the flood stage at some sites on the
Iowa River in Iowa. On the lower Green River in IL, a few reports of
some improvement in the amount of water and ice spilling out of
bankfull levels, as well as reduced pressure on the levee near
Colona. But with still some ongoing uncertainties, will have to keep
watch over this area for hydro impacts at least into the evening.

The rivers area-wide in general will have to be watched for more ice
action and jams, possibly producing additional flooding during the
rest of the week of unseasonably mild weather and more rainfall. ..12..

&&

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

&&

$$

SYNOPSIS...08
SHORT TERM...08
LONG TERM...12
AVIATION...Nichols
HYDROLOGY...12


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