Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 241759 AAC
AFDDVN

Area Forecast Discussion...UPDATED
National Weather Service Quad Cities IA IL
1159 AM CST Fri Feb 24 2017

...AVIATION UPDATE...

.UPDATE...
Issued at 959 AM CST Fri Feb 24 2017

Update to the WSW mentioning ice accumulations. Report from
Delaware County and road crews are that slick spots with ice are
showing up. With warmer temps aloft, rain falling in the area will
quickly cause the surface temps to cool below freezing. Expect up
to 0.10 inches of ice across the advisory area, especially on
raised surfaces.

&&

.SYNOPSIS...
Issued at 340 AM CST Fri Feb 24 2017

Low pressure was situated over central MO with the strongest
forcing and thunderstorms shifting to our north and northeast.
At 3 am only a few showers were noted in our eastern cwa moving
rapidly to the northeast. Temperatures ranged from 32 at Independence
to the upper 40s in our se cwa. Quincy, IL had 60 degrees.

Elsewhere, snow was falling from western and northern IA into
southern MN and central WI.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 340 AM CST Fri Feb 24 2017

Headlines: Pushed the start time to 9 am in our far nw, otherwise
remains the same.

Today: Complicated forecast as low pressure is not as deep and is
farther south than earlier expected. Low pressure should push to
central or northeast Il this afternoon and then into sw Lower MI
by evening. The changeover from rain to snow looks delayed this
morning and pavement temperatures in our nw cwa were still in the
mid 30s. This reduces the threat of any freezing rain and with the
changeover expected later this morning have pushed the start time
of the winter weather advisory to 9 am. The HRRR brings the
deformation zone into our cwa this afternoon while other models
bring it in later this morning. The next shift may need to adjust
the timing once again depending on precipitation/temperatures trends.
There is the potential for up to an inch of snow in our nw by the
end of the day, but the impacts to this mornings commute appear
minimal. maximum temperatures will range from the lower 30s in
our far nw to the lower 50s far se.

Convection: SPC has only our far eastern counties in a marginal
risk of severe storms which would be this morning, but the
instability is minimal. By afternoon the instability becomes much
better well to our east as the surface low tracks towards
northeast IL. Any storms this morning ahead of the surface low in
the marginal risk area could produce hail up to 1 inch.

Tonight: The transition to all snow will occur from west to east over
the remainder of the cwa this evening but the snow will diminish
from west to east after midnight. Total accumulations from this
event should range from about 2.5 inches at Independence to 1 to 2
inches over our nw half, with less than an inch in our se half.
Temperatures will be much colder along with brisk northwest winds
gusting to around 30 mph. Lows should range from the upper teens
at Independence to the lower to mid 20s elsewhere. This will
definitely feel more like winter with wind chills dipping into the
single digits and lower teens.

.LONG TERM...(Saturday through Thursday)
ISSUED AT 340 AM CST Fri Feb 24 2017

Saturday will feel much more winterlike over the area with brisk
northwest winds from 20 to 30 mph and wind chills only in the single
digits and teens to start the day. Will keep a low chance for light
snow over the east early, but the latest model timing of the upper
level wave and in-building subsidence suggests only flurries with no
additional accumulation. The strong winds may cause some drifting
snow over the northwest and north, especially early in the morning.
The subsidence and more anticyclonic low level flow should lead to
clearing skies in the afternoon, allowing temperatures to recover to
the mid to upper 20s over the snow covered north, and lower to mid
30s south. A quick transition to a zonal flow aloft and likely
return of cloud cover overnight into Sunday will prevent the typical
post system cold dump with the passing surface ridge and thus have
lows only in the 20s, then highs returning to the upper 30s to mid
40s Sunday as warm advection commences. Based mainly on possibility
of a scenario close to the outlier, wetter GFS, will mention low
chances for rain Sunday afternoon over mainly the southeast ahead of
a weak cold front.

Another low pressure system, albeit much weaker, is progged to lift
northeast over or just northwest of the forecast area Tuesday into
Tuesday night. Warm air advection will likely push highs into the
40s Monday, then the 50s to possibly lower 60s Tuesday, depending on
the system`s timing. Precipitation breaking out in advance will
likely be mainly in the form of rain with this system as the warm
sector will likely encompass most of the area Monday night into at
least the first half of Tuesday. The upper flow is shown becoming
more northwesterly following the upper trough`s passage Wed into Thu
with a system pushing through the Great Lakes possibly resulting in
some precipitation Thursday. Temperatures are low confidence in
these periods due to large differences in the amount of cold air
shown pushing into the area in the NW flow. The blended model
approach for now results in late week forecast highs from the upper
30s north to upper 40s south and lows in the 20s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
ISSUED AT 1159 AM CST Fri Feb 24 2017

Next 18 hours of the TAF period will feature freezing
precipitation and LIFR and IFR cigs and vsbys. In the next 6 hours
most TAF sites will have cigs and vsbys in the MVFR to LIFR. The
best chance for frozen precip will occur after 00z with the
exception of DBQ that will have some FZDZ. Later in the period,
precipitation should stop and we will see improvements to the cigs
and vsbys.

&&

.HYDROLOGY...
Issued at 307 PM CST Thu Feb 23 2017

Forecast rainfall from the event today and tomorrow along with
routed flow north of the area will lead to rises on area streams
and rivers. The Iowa and Cedar rivers are forecast to see rises
that are dependent on forecast rainfall through this event.
Conesville and Marengo are forecast to reach flood stage this
weekend. With low confidence in total rainfall amounts, these
sites have been placed in a Flood Watch. Columbus Junction,
Wapello, Oakville and DeWitt are forecast to reach flood late this
weekend and into next week. With the low confidence in rainfall
totals and these rivers forecast to reach flood past 48 hours,
flood watches were not issued at this time.

Forecast rises on the Mississippi River are expected through the
period as routed flow moves through the system. Some of this flow
in contingent on rainfall through Saturday. Regardless of this,
the river is going up. Some sites could see flood warnings in the
next week or two.

As confidence increases in the potential for river flooding,
additional watches and warnings could be issued.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Winter Weather Advisory until 6 AM CST Saturday for Benton-
     Buchanan-Delaware-Dubuque-Jones-Linn.

IL...NONE.
MO...NONE.
&&

$$

UPDATE...Gibbs
SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...Sheets
AVIATION...Gibbs
HYDROLOGY...Gibbs



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