Flood Potential Outlook
Issued by NWS Quad Cities, IA IL

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IAC011-019-031-045-055-057-061-087-095-097-101-103-105-107-111-113-
115-139-163-177-183-ILC011-015-067-071-073-085-109-131-155-161-177-
187-195-MOC045-199-151800-

Probabilistic Hydrologic Outlook
National Weather Service Quad Cities IA IL
1036 AM CST Thu Feb 25 2021

...Only Minor Changes in Flood Risk in the Past 2 Weeks...

.2021 Spring Flood and Water Resources Outlook #2...

This is the second of three planned Spring Flood and Water Resource
Outlooks for 2021 for the Quad Cities Hydrologic Service Area, which
covers portions of eastern Iowa, northwest and west central
Illinois, and extreme northeast Missouri. Rivers included in this
outlook are the Mississippi River and its tributaries from above
Dubuque, Iowa to below Gregory Landing, Missouri. The primary
tributary systems include the Maquoketa, Wapsipinicon, Cedar,
English, Iowa, Skunk, North Skunk, and Des Moines Rivers in Iowa;
the Fox River in Missouri; and the Pecatonica, Rock, and Green
Rivers in Illinois, as well as the La Moine River in Illinois. This
outlook is for the time period from March through May.

.Flood Outlook Overview...

Active weather this winter season created a deep snowpack across
eastern Iowa and into northern Illinois, which is the main factor
for flood risk this spring. However, it should be known that while
there is a significant snowpack locally, the overall flood risk is
less than what has been in place the past 2 years.

In general, the risk for flooding on the Mississippi River remains
near normal this spring, while there is an above normal chance for
Minor flooding near and downstream on the Quad Cities. Local rivers
have a range in risk probabilities, which is dependent on the nature
of the snowpack across each particular watershed. Most watersheds
are displaying conditions indicating flood risk this spring will be
near to above normal.

Recent warm weather has allowed melting of the snowpack to
begin, with some of the southern watersheds having already lost much
of the snow cover, with rises being observed in many smaller rivers
and creeks. With the loss of snow in these watersheds, any
spring flooding will be dependent on additional snow yet this season
or on spring rainfall. Local rivers of highest concern for flooding
to occur are the Rock River, as well as smaller rivers and creeks
across eastern Iowa into northern Illinois where a deep snowpack
remains.

.Key Takeaways...

* Flood risk this season is lower than previous years, with
  widespread Minor Flooding having the highest risk.

* Snowpack and water equivalent in the snowpack are well above
  normal across portions of eastern Iowa and into northern Illinois.
  Areas upstream through the remainder of the Upper Mississippi
  River watershed are averaging below normal snowpack and snow water
  equivalent.

* Early winter warm temperatures combined with the deep snowpack to
  keep the ground from freezing extensively during the extreme cold
  in February. Frost depths remain shallower than normal, so frozen
  ground will not be a key contributor to flood risk this spring.

* Near to below normal soil moisture over much of the region will
  reduce the flood risk as well as reduce the risk for long term
  flooding.

* While watersheds in the area with a deep snowpack will see an
  increased risk for flooding, the degree of flooding will depend on
  the rate of snowmelt, in combination with additional spring
  precipitation.

Many factors are considered when determining the overall flood risk
for the upcoming spring season. The combination of these influences
factor into the final determination. These factors are discussed in
detail below.


.Seasonal Precipitation:
     Local Rivers - Increased Flood Risk
     Mississippi River - Decreased to Near Normal Flood Risk

Precipitation this winter has averaged above normal for much of the
NWS Quad Cities Hydrologic Service Area (HSA), however the larger-
scale Upper Mississippi River watershed has averaged near to below
normal precipitation.

Despite the above normal precipitation through the winter,
precipitation since mid February has been near to below normal
across the region. Adding only small amounts of moisture to the
snowpack and river systems through the end of February has had little
impact on the flood risk when compared to the initial outlook.

Watersheds that have received above normal precipitation this winter
will see an increased risk of flooding this spring. Conversely,
watersheds that have received near to below normal precipitation
this winter will not see the flood threat increased due to seasonal
precipitation.


.Snow Cover and Liquid Water Content:
     Local Rivers - Increased Flood Risk
     Mississippi River - Near Normal to Increased Flood Risk

As of late February, snow cover remains across much of the Upper
Mississippi River watershed, which extends into much of Minnesota and
Wisconsin. Warm weather in late February has caused melting of the
snow, particularly in the extremities of the snowpack over western
Minnesota, western and southern Iowa, and central Illinois. However,
looking at areas that do continue to have snow cover, when compared
to normal values, snow depths across eastern Iowa and northern
Illinois remain well above normal, with below normal snow cover
observed to the north through much of Minnesota and Wisconsin.

The local area continues to have some of the deepest snowpack in the
region, which again, is well above normal. From central Iowa through
northern Illinois, the snowpack ranges from 8 to 16 inches in depth,
with lesser amounts going through the southern part of the forecast
area. The far southern counties in the Quad Cities Hydrologic
Service Area across far northeast Missouri, far southeast Iowa, and
west central Illinois have observed most of the snow cover melt
during the third week of February. Much of the remaining snowpack
also has a thick layer of embedded ice due to rain and freezing rain
that fell in January. The majority of the snowpack across the local
area contains liquid equivalent amounts of 2 to 4 inches, with the
heaviest being over east central Iowa into northern Illinois.

Looking across northern Iowa, Minnesota, and the northern half of
Wisconsin, which includes areas that feed the Des Moines, Cedar,
Iowa, Wapsipinicon, and Mississippi Rivers, the majority of the
region is observing below normal snow depths and liquid water
content in the snowpack.

With above freezing temperatures expected in the coming weeks, the
snowpack will likely continue to observe melting and decrease in
areal coverage creating runoff into area rivers.


.Soil Conditions: Decreased Flood Risk

Soils across much of the Upper Mississippi River watershed are near
normal or drier than normal, with the driest soils being indicated
across the western parts of Minnesota and Iowa, as well as central
Illinois.

Despite the overall drier conditions there is a swath of higher soil
moisture from east central Iowa into southern Wisconsin, which
highlights the locations that received above normal precipitation
during the fall of 2020. This area is fairly small, so while higher
soil moisture may increase the flood risk slightly in those local
areas, it does not have a significant impact on overall flood
concern across the region.

As a whole, soil conditions are not favorable to enhance flood
concerns, but with melting snow, it is likely to see soil moisture
increase in the coming weeks.


.Frost Depth: Decreased Flood Risk

Warm temperatures earlier this winter kept the ground from freezing.
Then, deep snowpack was established and acted to insulate the ground
during the February cold snap, which prevented deep frost
development. Even with the recent cold conditions, frost depths
across eastern Iowa, northeast Missouri, and western to northwest
Illinois are quite shallow, frozen to depths of less than 12 inches,
with many areas less than 6 inches. There are some locations with
deeper frozen ground, especially going north in the region, but
overall frost depths are below normal and will not contribute to a
higher flood risk.


.River Conditions: Near Normal Flood Risk

Streamflow analysis from the United States Geological Survey
indicates the majority of the Upper Mississippi River watershed has
rivers running at near normal streamflows. The near normal
streamflows do not cause an increased or decreased risk of flooding
this spring. However, with runoff expected in the coming weeks with
melting snow, streamflows are likely to increase through early March.


.Ice Jam Flooding: Risk Increasing for Breakup Jams

After mild conditions through January kept river ice at a minimum,
the extreme cold in February caused ice to develop on area rivers.
However, the cold air did not have enough residence time to cause
extremely thick ice, which would be more conducive to ice jams
developing when the ice breaks up.

While current conditions don`t favor an overly high risk for break
up ice jams, as long as there is ice on the rivers there is
potential for ice jams. A factor that would increase this risk would
be a quick rise in river flows from extreme snowmelt runoff or
rainfall, which are conditions that will be monitored in the coming
weeks.

The lack of thick ice also allowed some areas to start to see the
river ice break up already as temperatures have warmed this past
week. This trend may continue through the first weeks of March as
temperatures continue to moderate.


.Weather Outlooks:

According to the latest climate outlooks from the Climate Prediction
Center, the trend for March is for warmer than normal temperatures
favored across much of Iowa, Illinois, and Missouri, with lesser
signal for above, near, or below normal in areas to the north. For
precipitation, areas that will have higher probabilities for above
normal precipitation are the Great Lakes areas into the Ohio River
Valley.

The three month outlook for March through May is very similar to the
week 2 outlook, indicating a similar weather pattern to stay in
place with temperatures favoring above normal on average, with the
above normal precipitation favored over the Great lakes and Ohio
River Valley and below normal conditions favored to the west, in the
plains and Intermountain West.


.Summary:

While there are some area rivers with a higher risk for flooding
than normal this spring, the threat is highest for Minor Flooding to
occur. The overall risk for flooding is lower than in the previous
two years.

The relatively higher flood risk remains on rivers across eastern
Iowa and northwest Illinois, where the majority of the watershed
contains an above normal snowpack. Much of this area is also where
the higher soil moisture resides, which further increases the flood
risk. Smaller rivers and creeks in these areas will also have a risk
for flooding as the snowmelt progresses.

Looking at the Mississippi River, the near to below normal snowpack
across the upper part of the watershed, combined with the drier soil
conditions will keep the risk for flooding near normal for areas
upstream of the Quad Cities. With more flow coming into the river
downstream of the Quad Cities, including inputs from the Rock, Iowa,
English, Skunk, and Des Moines Rivers, the risk for minor flooding
is higher than normal, with the risk for reaching higher flood
categories near normal.

For rivers across eastern Iowa, northwest and west central Illinois,
and far northeast Missouri, the risk for flooding this spring is
concentrated on the snowpack and the rate that it melts. As there
are some areas where the snowpack has already melted, these rivers
have a reduced flood risk for this spring, as they are now reliant
on additional snowfall and spring rains to see river rises reach
flood levels.

The amount of liquid water available in the snowpack itself leads to
a higher than normal risk for minor flooding. However, with soil
conditions being drier, along with the shallow frost, there is the
likelihood for sufficient absorption of snowmelt and spring rainfall
into the soils, which reduces the risk for flooding.


.Numerical Probabilistic River Outlooks...

These numbers provide long-range probabilistic river outlooks for
river basins in the NWS Quad Cities service area. This data is
divided into three parts, the first part for the probabilities of
minor, moderate and major flooding, the second part for high water
and the final part for low water.

In Table 1 below, the current (CS) and historical (HS) or normal
probabilities of exceeding minor, moderate and major flood stages
are listed for the valid time period.

CS values indicate the probability of reaching a flood category
based on current conditions.

HS values indicate the probability of reaching a flood category
based on historical or normal conditions.

When the value of CS is greater than HS, the probability of
exceeding that level is higher than normal. When the value of CS
is less than HS, the probability of exceeding that level is lower
than normal.


...Table 1--Probabilities for minor, moderate and major flooding...
                    Valid Period:  03/01/2021 - 05/30/2021

                                       :    Current and Historical
                                       :     Chances of Exceeding
                                       :       Flood Categories
                                       :      as a Percentage (%)
                      Categorical      :
                   Flood Stages (ft)   :   Minor    Moderate   Major
Location           Minor   Mod   Major :  CS   HS   CS   HS   CS   HS
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Mississippi River
Dubuque LD11        16.0   17.0   20.5 :  41   48   28   39   10   12
Dubuque             17.0   18.0   21.5 :  53   54   39   46   15   15
Bellevue LD12       17.0   18.0   20.0 :  28   38   17   32   10   12
Fulton LD13         16.0   18.0   20.0 :  50   52   24   35   15   14
Camanche            17.0   18.5   20.5 :  41   46   25   35   15   14
Le Claire LD14      11.0   12.0   13.5 :  46   52   31   37   16   20
Rock Island LD15    15.0   16.0   18.0 :  63   59   48   52   23   25
Ill. City LD16      15.0   16.0   18.0 :  59   59   45   48   24   25
Muscatine           16.0   18.0   20.0 :  68   62   45   48   24   25
New Boston LD17     15.0   16.5   18.5 :  75   64   49   52   30   32
Keithsburg          14.0   15.5   17.0 :  73   64   47   50   30   28
Gladstone LD18      10.0   12.0   14.0 :  74   64   45   48   24   24
Burlington          15.0   16.5   18.0 :  73   63   46   48   28   28
Keokuk LD19         16.0   17.5   19.0 :  47   48   30   34   21   22
Gregory Landing     15.0   18.0   25.0 :  75   64   38   43   <5   <5

:Maquoketa River
Manchester Hwy 20   14.0   17.0   20.0 :  27   23   16   17    5    6
Maquoketa           24.0   26.0   28.5 :  18   16   11   12   <5    6

:Wapsipinicon River
Independence        12.0   13.0   15.0 :   7    8    6    7   <5   <5
Anamosa Shaw Rd     14.5   18.0   21.5 :  22   26   10   13   <5   <5
De Witt 4S          11.0   11.5   12.5 :  93   72   86   65   59   42

:North Skunk River
Sigourney           16.0   18.0   21.0 :  66   55   40   41   15   13

:Skunk River
Augusta             15.0   17.0   20.0 :  55   40   35   30   16   15

:Cedar River
Vinton              15.0   18.0   19.0 :  14   19   <5    7   <5   <5
Palo Blairs Ferry   12.5   15.5   17.0 :  17   22   <5    6   <5   <5
Cedar Rapids        12.0   14.0   16.0 :  18   27    9   14    7    9
Cedar Bluff         16.0   20.0   26.0 :  20   33    7    9   <5   <5
Conesville          13.0   15.0   16.5 :  68   56   19   27    7    8

:Iowa River
Marengo             15.0   17.0   19.0 :  77   69   43   44    7    6
Iowa City           23.5   24.5   26.0 :  <5   <5   <5   <5   <5   <5
Lone Tree           16.0   18.5   22.0 :  20   16    6    7   <5   <5
Columbus Jct        23.0   25.0   26.5 :  14   12    6    6   <5   <5
Wapello             21.0   25.0   27.5 :  49   47    7    6   <5   <5
Oakville            11.0   15.0   20.0 :  28   30   <5   <5   <5   <5

:English River
Kalona              14.0   16.0   18.0 :  74   50   41   34   16   15

:Des Moines River
Keosauqua           22.0   25.0   27.0 :   9   12   <5   <5   <5   <5
St Francisville     18.0   22.0   25.0 :  33   40    8    8   <5   <5

:Fox River
Wayland             15.0   18.0   20.0 :  26   24   12   13   <5   <5

:Pecatonica River
Freeport            13.0   14.0   16.0 :  50   34   28   18    5   <5

:Rock River
Como                12.5   15.5   18.0 :  44   20   10   10   <5   <5
Joslin              12.0   14.0   16.5 :  85   53   53   25   19   14
Moline              12.0   13.0   14.0 :  81   54   62   28   41   19

:Green River
Geneseo             15.0   16.5   18.0 :  39   24   11   13    6   <5

:La Moine River
Colmar              20.0   22.0   24.0 :  57   61   47   42   21   20

Legend
CS = Conditional Simulation (Current Outlook)
HS = Historical Simulation
ft = Feet


In Table 2 below, the 95 through 5 percent columns indicate the
probability of exceeding the listed stage levels (ft) for the valid
time period.

...Table 2--Exceedance Probabilities...

                               Chance of Exceeding Stages
                                  at Specific Locations
                          Valid Period: 03/01/2021 - 05/30/2021
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Mississippi River
Dubuque LD11         10.4   11.6   13.1   15.5   17.6   20.6   21.8
Dubuque              12.2   13.4   15.1   17.3   19.3   22.4   23.8
Bellevue LD12        11.1   12.3   13.6   15.6   17.3   20.0   21.2
Fulton LD13          10.9   12.1   13.7   16.0   18.0   20.7   22.1
Camanche             12.6   13.4   14.5   16.6   18.5   21.2   22.8
Le Claire LD14        8.1    8.7    9.6   10.9   12.3   14.6   16.0
Rock Island LD15     11.4   12.3   14.2   15.8   17.7   19.9   21.3
Ill. City LD16       11.0   12.0   13.8   15.4   17.7   20.4   22.4
Muscatine            12.4   13.5   15.5   17.2   19.7   22.1   23.8
New Boston LD17      12.4   13.3   15.1   16.5   18.9   21.2   22.7
Keithsburg           12.1   12.6   13.7   15.4   17.5   19.5   20.6
Gladstone LD18        8.1    8.6    9.8   11.7   13.7   16.5   17.7
Burlington           13.2   13.6   14.8   16.2   18.3   20.8   21.9
Keokuk LD19          10.1   11.1   13.3   15.8   18.2   21.5   23.0
Gregory Landing      11.6   12.6   14.9   17.1   19.2   22.7   24.2

:Maquoketa River
Manchester Hwy 20     8.1    8.4    9.1   10.6   14.5   18.3   20.1
Maquoketa            15.9   16.5   17.9   19.8   22.1   26.2   28.2

:Wapsipinicon River
Independence          6.1    6.3    7.0    7.9    9.1   11.5   14.7
Anamosa Shaw Rd       8.4    9.3   10.4   11.8   14.2   18.3   20.2
De Witt 4S           10.8   11.2   12.1   12.6   13.2   13.7   13.8

:North Skunk River
Sigourney            12.6   14.5   15.8   17.6   19.6   22.5   23.2

:Skunk River
Augusta               8.9    9.8   11.9   15.5   18.9   22.3   24.8

:Cedar River
Vinton                7.1    7.7    9.7   11.4   13.0   15.8   17.7
Palo Blairs Ferry     6.9    7.4    8.5    9.7   11.1   13.2   15.1
Cedar Rapids          5.9    6.3    7.3    8.5   10.6   13.8   17.2
Cedar Bluff           9.3   10.0   11.4   12.8   15.5   18.3   21.6
Conesville           11.3   11.8   12.7   13.6   14.5   15.9   16.9

:Iowa River
Marengo              12.4   13.7   15.7   16.9   18.0   18.9   19.3
Iowa City            15.6   16.6   18.7   19.2   19.2   19.5   23.3
Lone Tree            12.7   13.4   14.3   14.5   15.1   17.4   19.2
Columbus Jct         16.7   17.3   18.6   19.6   21.3   24.1   25.3
Wapello              18.7   19.2   20.3   21.0   22.3   24.1   25.6
Oakville              7.8    8.4    9.4   10.1   11.4   13.1   14.7

:English River
Kalona               12.0   12.6   13.9   15.3   17.0   18.9   20.4

:Des Moines River
Keosauqua            13.4   13.7   16.9   18.6   20.4   21.5   24.0
St Francisville      10.8   11.1   14.9   16.9   19.5   21.0   24.1

:Fox River
Wayland               6.8    6.9    8.9   11.9   15.2   18.2   19.7

:Pecatonica River
Freeport             11.2   11.5   12.2   13.0   14.1   15.1   16.0

:Rock River
Como                  8.6    9.2   10.2   11.9   13.4   15.5   16.6
Joslin               11.2   11.6   12.8   14.3   15.8   18.3   20.2
Moline               11.1   11.4   12.2   13.5   14.7   16.2   18.8

:Green River
Geneseo               8.7    9.5   11.2   13.6   15.5   16.6   18.1

:La Moine River
Colmar               10.5   12.9   16.7   21.6   23.6   25.1   26.2


In Table 3 below, the 95 through 5 percent columns indicate the
probability of falling below the listed stage levels (ft) for the
valid time period.

...Table 3--Non-Exceedance Probabilities...

                            Chance of Falling Below Stages
                                 at Specific Locations
                          Valid Period: 03/01/2021 - 05/30/2021
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Mississippi River
Dubuque LD11          4.4    4.4    4.3    4.3    4.3    4.2    4.2
Dubuque               7.5    7.5    7.4    7.4    7.4    7.3    7.3
Bellevue LD12         4.0    4.0    3.9    3.9    3.8    3.7    3.7
Fulton LD13           4.5    4.5    4.4    4.4    4.4    4.3    4.3
Camanche              8.8    8.8    8.8    8.8    8.8    8.8    8.8
Le Claire LD14        4.6    4.6    4.5    4.5    4.5    4.5    4.4
Rock Island LD15      4.9    4.9    4.8    4.7    4.6    4.5    4.4
Ill. City LD16        4.1    4.0    4.0    3.9    3.8    3.7    3.6
Muscatine             6.3    6.3    6.3    6.2    6.2    6.1    6.1
New Boston LD17       4.2    4.2    4.1    4.0    3.9    3.8    3.7
Keithsburg            6.1    6.0    5.9    5.9    5.8    5.8    5.7
Gladstone LD18        1.8    1.8    1.7    1.6    1.5    1.4    1.3
Burlington            8.2    8.2    8.1    8.1    8.0    7.9    7.8
Keokuk LD19           4.9    4.8    4.7    4.4    4.1    3.7    3.0
Gregory Landing       6.7    6.7    6.7    6.6    6.5    6.4    6.3

:Maquoketa River
Manchester Hwy 20     4.2    4.2    4.2    4.2    4.2    4.2    4.2
Maquoketa            10.4   10.4   10.3   10.3   10.3   10.2   10.2

:Wapsipinicon River
Independence          4.8    4.8    4.8    4.8    4.8    4.8    4.8
Anamosa Shaw Rd       5.0    4.9    4.9    4.9    4.9    4.9    4.9
De Witt 4S            5.5    5.4    5.3    5.3    5.3    5.2    5.2

:North Skunk River
Sigourney             5.7    5.6    5.3    5.0    4.8    4.3    4.2

:Skunk River
Augusta               4.0    3.7    3.3    2.8    2.2    1.8    1.5

:Cedar River
Vinton                1.6    1.6    1.6    1.6    1.6    1.6    1.6
Palo Blairs Ferry     2.0    2.0    1.9    1.9    1.9    1.9    1.9
Cedar Rapids          3.2    3.2    3.2    3.2    3.2    3.2    3.2
Cedar Bluff           3.8    3.8    3.8    3.8    3.7    3.7    3.7
Conesville            5.4    5.4    5.4    5.3    5.3    5.2    5.2

:Iowa River
Marengo               5.7    5.7    5.7    5.7    5.7    5.6    5.6
Iowa City            10.1   10.1   10.1   10.0    9.5    9.2    9.2
Lone Tree             5.6    5.4    5.3    5.2    4.5    4.1    4.0
Columbus Jct          9.6    9.5    9.4    9.3    9.2    9.0    8.9
Wapello              11.8   11.8   11.6   11.5   11.3   11.1   10.8
Oakville              1.8    1.8    1.7    1.6    1.4    1.1    0.8

:English River
Kalona                4.8    4.7    4.5    4.3    4.2    3.9    3.9

:Des Moines River
Keosauqua            12.3   12.0   11.7   11.2   10.6   10.2   10.0
St Francisville       9.4    8.7    8.4    7.5    6.8    6.1    5.9

:Fox River
Wayland               2.2    2.2    2.1    1.9    1.8    1.7    1.6

:Pecatonica River
Freeport              5.4    5.2    5.1    4.9    4.8    4.5    4.4

:Rock River
Como                  4.5    4.4    4.4    4.3    4.1    3.9    3.8
Joslin                6.1    6.0    5.9    5.8    5.7    5.4    5.2
Moline                8.8    8.8    8.7    8.7    8.5    8.3    8.2

:Green River
Geneseo               4.8    4.5    4.0    3.8    3.4    3.1    2.9

:La Moine River
Colmar                5.3    5.1    4.6    4.3    3.8    3.6    3.4

These long-range probabilistic outlooks contain forecast values that
are calculated using multiple season scenarios from 30 or more years
of climatological data, including current conditions of the
river, soil moisture, snow cover, and 30 to 90 day long-range
outlooks of temperature and precipitation. By providing a range of
probabilities, the level of risk associated with long-range planning
decisions can be determined. These probabilistic forecasts are part
of the National Weather Service`s Advanced Hydrologic Prediction
Service.

Visit our web site at http://www.weather.gov/dvn for more weather and
water information.

The next outlook will be issued on March 11, 2021.

$$

Brooks






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