Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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589
FXUS63 KDVN 210517
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1117 PM CST Tue Feb 20 2018

...AVIATION UPDATE...

.UPDATE...
Issued at 536 PM CST Tue Feb 20 2018

The rain is now shifting east of the Mississippi River, and as
temperatures there are just reaching freezing. That will likely
allow us to clear out the southeast Iowa counties and northeast
Missouri counties early from the advisory.
ERVIN

UPDATE Issued at 400 PM CST Tue Feb 20 2018

The remainder of the flood watch has been cancelled as the bulk of
the rain has shifted south and east of the dvn cwa.

&&

.SYNOPSIS...
Issued at 325 PM CST Tue Feb 20 2018

Latest sfc analysis was indicating occluding low acrs the U.P. of
MI, with main trailing cold front dropping down acrs north central
IL and then down toward the St Louis MO area. Seasonably impressive
long fetch moist conveyor of showers with some embedded thunder
stretching all the way from southern TX, to the heart of the GRT
LKS. Post-frontal northwest winds increasing to 15 to 20 KTS acrs
the western CWA, with some drier sfc DPT influx noted. This will
eventually lead to a wintry mix scenario again on the western flank
of lingering over-running precip band this evening. Then active
southwest flow will continue to make for a challenging fcst period
with precip system possible almost every other day into the
weekend.

&&

.SHORT TERM...(This Evening and Tonight)
ISSUED AT 325 PM CST Tue Feb 20 2018

Tonight...With post frontal cooling and drying LLVL fetch feeding
into the backside of the rather slow moving precip conveyor, feel
there will be another transition to freezing rain profiles as the
late afternoon and especially evening progress...especially along
and east of the MS RVR generally from far northeastern MO,
northeastward to the Princeton and Sterling IL areas. Toward the end
of the period, cold air may deepen enough for some sleet to mix in,
before the precip train pushes off to the east. Will issue a new
Winter Weather Advisory for primarily the freezing rain acrs the
southeastern third or more of the DVN CWA, with up to a tenth of an
inch of glaze possible. Will run it to 09z Wed morning for a buffer
end time , but several of the latest HiRes models wind it down
several hours before then. The rest of the CWA will have to watch
out for freezing up wet surfaces and puddles this evening, if the
increasing northwest winds don`t dry up the surfaces before then.
Flurries noted in the stratocu deck out acrs central into western IA
ATTM, and some of these may make it into the local area later this
evening. Will go with lows in the low 20s in the east, to the low
teens or around 10 in the northwest. These northwestern areas will
also have wind chills around or below zero toward 12z Wed morning.
..12..

.LONG TERM...(Wednesday through next Tuesday)
ISSUED AT 325 PM CST Tue Feb 20 2018

Forecast focus on active pattern through this weekend. This forecast
based heavily on the GFS, as the ECMWF was not available as of this
writing.

Wednesday...Mostly sunny but cold with highs in the mid 20s to lower
30s. Clouds should be on the increase during the afternoon
especially across our southern half of the cwa. This will be ahead
of the next upper level disturbance ejecting out the main western
trough.

Wednesday night and Thursday: Potential for a winter weather
advisory headline for our southern and western counties for a
combination of light snow and freezing rain. Forecast soundings
suggest the freezing rain may be confined to our southern cwa while
the snow would be in our north. During the afternoon, warmer air
coming northward would change everything over to rain. Lows will be
in the upper teens to mid 20s with afternoon highs in the 30s. As of
now, ice accumulations are expected to be less than a tenth of an
inch with snow amounts less than an inch.

Thursday night and Friday...Another upper level disturbance (and a
bit stronger) will push into the Midwest in the fast southwest flow.
This system will also have more moisture to work with. This also
looks to be a freezing rain event, especially in our northern half.
This too may need a winter weather advisory headline with ice
accumulations between one and two tenths of an inch possible. Warmer
air arriving by afternoon should change the freezing rain over to
rain. Lows will be in the 20s north to the 30s south with highs
pushing into the 40s.

Friday night through Sunday: A potent storm system will arrive as a
negatively-tilted trough pushes out of the southern Rockies and into
the Midwest during this time frame. The GFS takes a deepening
cyclone from the OK Panhandle 12z Sat (1006 mb) to eastern IA 06z
Sun (991 mb) to the eastern Great Lakes (980mb) later on Sunday.
This may start out as light snow but change to light moderate rain
(possibly heavy rain) and then back to snow as the system pushes off
to the northeast. This system bears watching especially if the ECMWF
is on board. Any additional rain would aggravate any existing
flooding at that time. Caution: this is low confidence at this time
without seeing what the 12z/20 ECMWF showed.

Haase

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday Night)
ISSUED AT 1116 PM CST Tue Feb 20 2018

MVFR cigs are now clearing our of all of eastern Iowa and
northwest Illinois. Northwest winds of 12 to 20 kts will continue
to pump cold dry air into the region, with VFR conditions through
the next 24 hours.
ERVIN

&&

.HYDROLOGY...
Issued at 400 PM CST Tue Feb 20 2018

Rainfall since yesterday was 1 to 3 inches across much of the cwa.
This amount of rain, falling on frozen ground, has resulted in rapid
rises on many rivers and streams with several in flood. While there
is high confidence in these river forecasts at this time, these
forecasts may still change due to continued runoff and ice jams on
some rivers.

Details:

Rock River:

Major flooding is forecast at Moline, with moderate at Joslin and
minor at Como. The river will rise above flood stage
tonight into Wednesday morning.

La Moine/Green/Wapsipinicon River:

Moderate flooding is forecast at Colmar, Geneseo, and De Witt.

Maquoketa/English River:

Moderate flooding is forecast at Maquoketa and Kalona.

Pecatonica River:

Minor flooding is expected at Freeport.

Iowa River:

Minor flooding is expected at Marengo, Wapello and Lone Tree.

Other forecast points may also go into flood and we will
continue to monitor the situation.

In addition, an areal flood warning is in effect for portions of
northwest IL and extreme eastern IA until 1015 am on Wednesday. This
is because of numerous closed roads due to flooding. Additional
flooding is possible.

Please see the flood warnings and flood statements products for
updated forecasts.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...Winter Weather Advisory until 3 AM CST Wednesday for Bureau-
     Hancock-McDonough-Putnam-Warren.

MO...NONE.
&&

$$

UPDATE...Ervin
SYNOPSIS...12
SHORT TERM...12
LONG TERM...Haase
AVIATION...Ervin
HYDROLOGY...Haase



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