Flood Potential Outlook
Issued by NWS Central Illinois

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PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE LINCOLN IL
345 PM CST THU MAR 05 2015

...2015 SPRING FLOOD AND WATER RESOURCES OUTLOOK NUMBER 2...

...ABOVE NORMAL POTENTIAL FOR FLOODING ALONG THE ILLINOIS RIVER WITH
NEAR NORMAL PROBABILITIES ELSEWHERE ACROSS CENTRAL AND SOUTHEAST
ILLINOIS...

This flood outlook covers the Lincoln Hydrologic Service Area (HSA)
which encompasses 35 counties in central and southeast Illinois. It
includes the following rivers...

- Illinois River from Henry to Beardstown
- Spoon River from London Mills to Seville
- Mackinaw River at Congerville
- Sangamon River from Monticello to Chandlerville
- Salt Creek at Greenview
- Little Wabash River near Clay City
- Embarras River from Ste. Marie to Lawrenceville

These flood outlooks are issued in late winter and early spring, in
addition to the 7 day river forecasts that are issued when river
forecast locations are in flood or are forecast to rise above flood
stage. They are based on current streamflows, soil conditions, snow
pack, as well as short/long range weather forecasts.


FLOOD OUTLOOK HIGHLIGHTS...

The risk of flooding from the late winter into early spring is
overall near normal across most of central and southeast Illinois.
However, the likelihood for flooding along the Illinois River is
projected to be above normal this spring.

Those locations with near normal probabilities for flooding, or those
that usually flood in the spring will likely see typical conditions
this spring. Those locations with above normal probabilities will see
a greater chance of flooding when compared to a normal year.


WINTER WEATHER REVIEW...

--December--

Information, courtesy of the Illinois State Climatologist, shows that
December was both warmer and drier than normal. The statewide average
temperature in December was 33.4 degrees, 3.5 degrees above average
and the 29th warmest December on record. This follows a very cold
November that was 8.2 degrees below normal.

Across the ILX Hydrologic Service Area (HSA), monthly temperature
averages for December were well above normal, generally ranging from
2 to 5 degrees. Daily high temperatures ranged from the 20s to the
upper 50s. Normal highs for December range from the low 30s to the
mid 40s. Low temperatures ranged from around 10 degrees to the upper
40s in December. They normally range from the teens to the upper 20s.

The average statewide precipitation for December was 1.90 inches,
which is 0.80 inches below normal. The heaviest precipitation
(rainfall plus the water content of snow) was in southern Illinois,
which is typical for December. Precipitation amounts there were 3 to
5 inches. Much of the rest of the state, north of Interstate 70,
received 1 to 3 inches of precipitation. Snowfall was especially
light in December with many areas not seeing any snow. Portions of
western Illinois only received 1 to 2 inches.

Across the ILX HSA, precipitation totals for December were overall
below normal. Monthly precipitation totals ranged from 0.86 inches in
Galesburg to 4.25 inches in Olney. These totals ranged from 1.41
inches below normal to 0.37 inches above normal, respectively. This
equates to precipitation that roughly ranged from around 40 to 110
percent of normal.


--January--

The State Climatologist notes that Illinois was cooler and drier than
normal for the month of January. The statewide temperature was 25.4
degrees, 1 degree below normal and the 53rd coldest on record.

Across the ILX HSA, monthly temperature averages for January were
overall below normal with the exception of a few areas. Monthly
temperatures generally ranged from 1 degree below to 1 degree above
normal. Daily high temperatures ranged from the teens to the low 50s.
Normal highs for this month range from the low to mid 30s. Low
temperatures across the area ranged from the single digits below zero
to around 40 degrees. They typically range in the teens.

The statewide average precipitation for January 2015 was 1.53 inches,
0.5 inches below normal. Because of dry weather in November,
December, and January, the US Drought Monitor introduced the D0
classification, abnormally dry conditions, in northern and western
Illinois.  Snowfall ranged from less than an inch in the far south to
10 to 15 inches north of Interstate 80. This results in above normal
snowfall in the northern half of the state and below normal for the
southern half.

Across the ILX HSA, precipitation totals for January were below
normal. Monthly precipitation totals ranged from 0.96 inches in
Kincaid and Normal to 2.48 inches in Olney. These totals ranged from
1.17 to 0.57 inches below normal, respectively. This equates to
precipitation that ranged from roughly around 45 to 80 percent of
normal. January brought some appreciable snow to much of central
Illinois with monthly totals as high as 8 to 10 inches, while more
southern areas of the HSA saw much lesser amounts totaling only 1 to
3 inches.


--February--

The colder than normal temperature trend continued through the month
of February. The statewide average temperature for February was 18.6
degrees, which is 12.3 degrees below normal. It was the 7th coldest
February on record according to the Illinois State Climatologist.

Across the ILX HSA, monthly temperature averages for February were
well below normal. They generally ranged from 10 to 13 degrees below
normal. Daily high temperatures had a large range...single digits up
to around 60 degrees! Normal highs for February range from the mid
30s to the mid 40s. Low temperatures across the area ranged from the
teens below zero to the upper 30s. They normally range from the teens
to the upper 20s.

The statewide average precipitation for February was 1.50 inches
which is 0.50 inches below normal. Snowfall for February was well
above normal. Amounts of 15 to 20 inches were common across western
and northern Illinois while 10 to 15 inches were common elsewhere
across central and portions of southern Illinois. Snowfall totals
were greater than 200 percent of normal across the state with some
locations seeing greater than 300 percent of their normal monthly
snowfall for February.

Across the ILX HSA, precipitation totals for February were below
normal. Monthly precipitation totals ranged from 0.85 inches in
Normal to 2.37 inches in Hutsonville. These totals ranged from 1.08
to 0.22 inches below normal, respectively. This equates to
precipitation that ranged from roughly around 45 to 90 percent of
normal. As mentioned earlier, February brought some appreciable snow
to much of central Illinois with monthly totals generally ranging
from 8 to 14 inches. However, there were isolated locations with 18
up to 22 inches of snow!


SOIL MOISTURE AND FROST DEPTH CONDITIONS...

Soil moisture conditions across central and southeast Illinois are
overall near to above normal at shallow depths. However, deep soil
moisture levels are below normal for this time of year.

Drought conditions have not changed significantly over the winter
season. In late January, an area of D0 (Abnormally Dry) conditions
was introduced across west central and northern Illinois. However,
with the significant snow events through February, this was all but
erased. The latest drought monitor from March 3rd shows only a very
small area of DO in far northern Illinois. The remainder of Illinois
is not reporting any drought conditions at this time.

Frost depth conditions across central and southeast Illinois
generally range from 8 to 12 inches in depth. However, northernmost
areas were reporting frost depths of up to 19 inches.


RIVER CONDITIONS...

Currently, there is no river flooding being observed across central
and southeast Illinois. Information, courtesy of the U.S. Geological
Survey (USGS), shows that current streamflow conditions across
central and southeast Illinois are near normal to below normal for
this time of year.

With the long stretch of cold temperatures over the last few weeks,
many area rivers have continued to build ice. The ice has not reached
the point where it is creating significant impacts. However, with the
upcoming, significant warmup and associated snowmelt, there is the
potential for ice jams problems to develop.


WEATHER OUTLOOKS...

A significant warming trend is on the way over the next several days
with generally quiet weather across the region. High temperatures
this weekend will climb into the 40s with overnight lows below
freezing. As we head into next week, we can expect temperatures to
climb into the 50s...with 60s possible later in the week. Overnight
lows during that time will be in the 30s.

The 8 to 14 day outlook (Mar 12th to Mar 18th) indicates a greater
than 40 percent likelihood for above normal temperatures across the
southern half of Illinois with a greater than 50 percent likelihood
across the north.

The 30 day outlook for March indicates cooling trend toward the
latter half of the month with a greater that 33 percent likelihood
for below normal temperatures across most of Illinois. There are
equal chances for precipitation above, normal, or below normal during
this time frame.

The 90 day outlook (March, April, and May) for Illinois indicates
that there are equal chances for temperatures/precipitation above,
normal, or below normal during this period.


FLOOD OUTLOOK SUMMARY...

Above normal probabilities for flooding are forecast for the Illinois
River. Overall near normal probabilities for flooding exist elsewhere
across central and southeast Illinois. The likelihood for minor
flooding is highest along the Little Wabash River and portions of the
Embarras River this spring. However, these areas typically experience
at least minor flooding this time of year.

The main concern in the short term is the current snowpack of 4 to 6
inches across much of central and southeast Illinois. With the
significant warmup coming over the next several days, we will
effectively erase that snowpack. Thankfully, the weather will be
quiet during that time. With the ground frozen, most of the snowmelt
will run off into the river system. However, during the first few
days of the warmup we will see overnight lows below freezing which
will somewhat temper the melting process.

As a result of the snowmelt, river levels can be expected to rise
across central and southeast Illinois. There may be isolated
locations of minor river flooding, but nothing is expected to be
widespread. However with the still frozen ground, there are low-lying
areas that may see temporary ponding of water.

Many rivers across the area have built up an appreciable amount of
ice over the last few weeks. With the rising river levels there is
the possibility for the ice to breakup before it melts which could
create potential ice jam problems. As always, those people living
along or near rivers and streams should remain aware of the current
conditions in their area.

As we move ahead into the spring season, flooding will be mostly
driven by spring rains since there will likely be no additional
significant snowmelt contribution.


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 more 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:  3/9/2015 - 6/7/2015

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Illinois River
Henry               23.0   24.0   31.0 :  66   53   49   43   <5   <5
Peoria              18.0   22.0   28.0 :  76   64   32   27   <5   <5
Havana              14.0   17.0   23.0 :  81   70   46   41   <5   <5
Beardstown          14.0   18.0   28.0 :  90   76   61   52   <5   <5
:Mackinaw River
Congerville 2NW     13.0   14.0   20.0 :  18   16   15   15   <5   <5
:Spoon River
London Mills        15.0   21.0   24.0 :  44   44    7    7   <5   <5
Seville             22.0   25.0   30.0 :  40   41   20   16   <5   <5
:Sangamon River
Monticello          13.0   17.0   20.0 :  58   58    6    7   <5   <5
Riverton            23.0   26.0   29.0 :  13   13   <5   <5   <5   <5
Petersburg          23.0   24.0   33.0 :  15   13   12    9   <5   <5
:Salt Creek
Greenview           16.0   17.0   20.0 :  16   18   10   12    7    7
:Sangamon River
Oakford            471.0  472.9  478.5 :  29   30   13   13   <5   <5
Chandlerville      456.6  459.0  462.0 :  41   44   16   16   <5   <5
:Little Wabash River
Clay City           18.0   22.0   25.0 :  88   <5   17   <5   <5   <5
:Vermilion River
Danville            18.0   22.0   28.0 :  19   <5    8   <5   <5   <5
:Embarras River
Lawrenceville       30.0   37.0   41.0 :  80   <5   17   <5   <5   <5
Ste. Marie          19.0   20.0   27.0 :  42   <5   30   <5   <5   <5

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: 3/9/2015 - 6/7/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Illinois River
Henry                18.7   19.7   21.8   24.1   26.1   27.1   28.2
Peoria               13.9   15.7   18.2   20.6   22.6   23.5   24.9
Havana               12.8   13.7   14.9   16.9   18.6   20.4   21.6
Beardstown           13.2   14.5   16.5   20.2   23.7   25.8   26.8
:Mackinaw River
Congerville 2NW       4.2    5.1    6.5    9.3   11.7   15.7   16.6
:Spoon River
London Mills          8.8    8.9   11.6   14.4   18.3   20.9   22.3
Seville              12.5   12.8   15.9   19.7   24.6   26.9   27.6
:Sangamon River
Monticello           10.7   11.0   12.2   13.2   14.7   16.1   17.7
Riverton             14.2   14.7   16.7   18.7   21.6   23.9   26.0
Petersburg           11.7   12.4   14.0   16.5   20.5   24.2   28.9
:Salt Creek
Greenview             5.5    6.7    9.0   11.2   14.0   18.2   21.5
:Sangamon River
Oakford             462.6  463.3  465.6  468.6  471.4  473.8  475.5
Chandlerville       450.0  450.8  453.2  456.0  458.3  460.5  461.8
:Little Wabash River
Clay City            13.8   15.6   19.3   20.5   21.4   22.7   23.5
:Vermilion River
Danville              7.7    8.6   10.8   13.9   16.3   20.8   23.9
:Embarras River
Lawrenceville        26.3   28.0   31.1   33.5   35.6   38.4   40.0
Ste. Marie           10.7   11.2   15.0   18.4   20.5   22.0   24.0

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--Nonexceedance Probabilities...

                            Chance of Falling Below Stages
                                 at Specific Locations
                          Valid Period: 3/9/2015 - 6/7/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Illinois River
Henry                15.2   15.2   15.0   14.9   14.7   14.5   14.3
Peoria               12.4   12.3   12.2   12.0   10.7   10.6   10.6
Havana                7.5    7.4    6.7    5.8    5.0    4.9    4.8
Beardstown           10.6   10.6   10.2    9.9    9.6    9.4    9.1
:Mackinaw River
Congerville 2NW       2.0    1.8    1.5    1.3    1.2    1.0    1.0
:Spoon River
London Mills          3.9    3.7    3.4    3.2    2.8    2.5    2.4
Seville               7.3    6.9    6.6    6.2    5.8    5.4    5.3
:Sangamon River
Monticello            7.3    7.2    6.8    6.5    6.1    5.7    5.5
Riverton              7.3    6.4    5.6    4.8    4.3    3.9    3.8
Petersburg            7.7    7.3    6.6    6.1    5.7    5.4    5.4
:Salt Creek
Greenview             2.7    2.3    2.0    1.7    1.4    1.1    1.1
:Sangamon River
Oakford             459.1  458.6  457.9  457.5  456.9  456.7  456.5
Chandlerville       446.5  445.9  445.2  444.7  444.2  444.0  443.8

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.

---------------------------------------------------------------------

FLOOD TERMINOLOGY...

Minor flooding is used to indicate minimal or no property damage.
However, some public inconvenience is possible.

Moderate flooding is used to indicate some inundation of structures
and roads near the river. Transfer of property to a higher elevation
or another location may be necessary. Some evacuations may also be
required.

Major flooding is used to indicate extensive inundation and property
damage, usually characterized by the evacuation of people and
livestock and closure of both primary and secondary roads.

FOR MORE INFORMATION...

Visit our web page at www.weather.gov/ilx for more official NWS river
and weather information. To view graphical AHPS information,
including forecasts, select Rivers and Lakes from the list on the
left side menu. Full AHPS graphics are available for all forecast
points in the ILX HSA.

For 30 to 90 day temperature and precipitation outlooks, visit the
web page of the Climate Prediction Center at www.cpc.noaa.gov.

This will be the last issuance of the Spring Flood and Water
Resources Outlook for central and southeast Illinois unless
conditions warrant an update. The NOAA National Spring Flood Outlook
will be issued on Thursday, March 19th. National Flood Safety
Awareness Week is March 16th to the 20th.

$$

DRH




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