Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 221824
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
124 PM CDT THU SEP 22 2016

...Updated Hydrology Section...

.UPDATE...
Issued at 916 AM CDT Thu Sep 22 2016

MCS over northeast IA has continued to weaken considerably this
morning as it tracks mainly along Highway 20. Extensive cloud
cover has spread over much of the cwa so have updated the grids
to increase sky cover, and to lower maximum temperatures at least
a couple of degrees. The cloud cover will limit instability for a
while but more sunshine should occur as the afternoon progresses.
Additional convection should develop late this afternoon and
evening mainly north of Highway 30 and northward.

Rainfall last night across portions of northern IA/southern MN and
into western WI has ranged from 4 to 10 inches with some spots
receiving 14 inches of rain in the past 2 days. Much of this
water will be routed southward into the Cedar and Iowa Rivers.
See the latest flood watch and warning products.

&&

.SYNOPSIS...
Issued at 303 AM CDT Thu Sep 22 2016

At 3 am cdt...areas showers and thunderstorms are draped just northwest
of the region along and north of a stalled frontal system. Trends support
most or all of the most significant convection will stay to our NW
with episodes of convection making into the NW 1/3 the next 24 hours.
A backdoor cool front will arrive Friday that will tend to keep the
region drier and a bit cooler with less humidity.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 303 AM CDT Thu Sep 22 2016

Short term forecast confidence assessment...fair or average with main
concern next 24 hours if another outflow boundary impacts northern
sections today that could impact high temperatures by up to 3+ degrees
cooler. POPS in far NW 1/4 of the region also a challenge as will be
near the edge of favored rounds of convection.

Today...Generally partly to mostly sunny with some mostly cloudy skies
across the north. Chance or slight chance POPS over NW 1/3 of the region.
Highs again may be a challenge with near 80 degrees along highway 20
corridor to near 90 degrees along IA/MO border. Heat indices south 1/3
of the region may reach 90 for a few hours in the afternoon. Rain totals
of up to a half inch may be possible along the highway 20 corridor.
Strongest storms may produce gusty winds to around 40 MPH.

Tonight...Little change from the day with a slight shift south in the
rounds of convection. Additional one half inch or more of rain may be
north of highway 30. Since these areas past 5 plus days have been fairly
dry, no water issues expected. Lows still balmy for late September
in the mid to upper 60s.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 303 AM CDT Thu Sep 22 2016

Internally, the models are indicating there should be some type of
decaying convective complex across roughly the northern third of the
area Friday morning. The frontal boundary, that is projected to be
around I-80, and outflow boundaries from the convection are expected
to provide the focus for new convection Friday afternoon.

Cloud cover and precipitation along with the position of any meso
and synoptic scale boundaries does raise the possibility that
temperatures across the north half of the area `could` be much
cooler than forecast on Friday.

Friday night/Saturday dry conditions will be seen across the area as
high pressure quickly moves through the Midwest. Attention then
turns to the next approaching system.

Saturday night is interesting. The upper low will have ejected out
of the desert southwest. At the same time, energy from the remnants
of a western Pacific typhoon will top the ridge just off the west
coast. How these two pieces of energy will interact is key to the
sensible weather for the area. It is possible that the upper low may
eject out of the desert southwest slower than what the models are
indicating. If that occurs, Saturday night `could` end up being dry.

Right now the forecast has slight chance to chance pops for the
western half of the area Saturday evening with the eastern half
being dry. After midnight, all but the far east areas have a risk of
rain with the western third of the area having the best chance.

Sunday on...

There continues to be a wide disparity of the model solutions in
both timing and how energy in the northern stream interacts with the
cut off low. The GFS is quite progressive with the upper low. The
ECMWF and CMC models eject an open wave while developing another
upper low in the southern Rockies. Even with the ECMWF and CMC
models suggesting a similar scenario, both differ considerably with
the eastward movement of the system.

Right now the model consensus has a daily threat of rain for the
area from Sunday through Wednesday. There will be periods of dry
weather but there is no clear indication from the models when that
will occur.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
ISSUED AT 645 AM CDT Thu Sep 22 2016

Scattered convection will result in episodes of MVFR/IFR conditions
at CID/DBQ terminals the next 24 hours. Otherwise, mostly sunny south
and mostly cloudy north due to a stalled front nearly with ceilings
at or above 5k AGL. Winds will tend to be from the south at 5 to 15
MPH.

&&

.HYDROLOGY...
Issued at 1236 PM CDT Thu Sep 22 2016

Overview: Repeated rounds of very heavy rain have occurred over
northern Iowa, southeastern Minnesota, and western Wisconsin over
the past three days. A widespread 3 to 5 inches of rain has fallen
with isolated amounts of 6 to 9 inches. Additional heavy rainfall
is possible tonight and again Saturday night in the same general
area.

These extreme rainfall amounts will result in significant river
level rises downstream into eastern Iowa, including the
Mississippi River, into next week.

The majority of local river sites are now under either a flood
warning or flood watch as significant rises are forecast to begin
this weekend or early next week.

Warnings:

On the Cedar River, Iowa River, Wapsipinicon River (De Witt 4S),
and Mississippi River (sites Dubuque LD11 and Dubuque)

Confidence...Moderate on river level forecasts. Uncertainty arises
with respect to forecast crests, not on whether river levels will
exceed flood stage. How high rivers rise above moderate or major
flood stage is dependent on the downstream propagation of upstream
runoff. As new data is gathered over the coming days, forecast
confidence will likely increase.

Watches:

on the Mississippi River (all sites except Dubuque LD11 and
Dubuque) and Wapsipinicon River (Independence and Anamosa).

Confidence...Low to Moderate on river level forecasts because
river levels will depend on the amount of runoff that is routed
downstream through several tributary rivers. As new data is
gathered over the coming days, forecast confidence will likely
increase.

&&

.DVN Watches/Warnings/Advisories...
IA...None.
IL...None.
MO...None.
&&

$$

UPDATE...Haase
SYNOPSIS...Nichols
SHORT TERM...Nichols
LONG TERM...08
AVIATION...Nichols
HYDROLOGY...Uttech/Brooks



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