Flood Potential Outlook
Issued by NWS Central Illinois

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PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE LINCOLN IL
453 PM CST THU FEB 19 2015

...2015 SPRING FLOOD AND WATER RESOURCES OUTLOOK NUMBER 1...

...ABOVE NORMAL POTENTIAL FOR MINOR 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 minor 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--

Heading into February, the colder than normal trend continued.
Snowfall amounts thus far in February have taken a considerable jump
thanks to two storm systems that impacted different areas of the
state.

The first storm impacted mainly the northern third of Illinois at the
beginning of the month and brought record snowfall amounts to the
Chicagoland area. The highest totals for this event ranged from 12 to
more than 20 inches. This storm was the 5th largest in Chicago
history.

The second, and most recent, storm from mid this month impacted
mainly the southern third of Illinois. Snowfall totals of between 4
to 8 inches were common with isolated amounts of 12 inches in
southernmost sections of the state.

As a result of these two systems, the month to date snowfall across
most of the state generally ranged from 1 to 8 inches above normal.
The exception is the northeast, which is running 8 to 12 inches above
normal.

As of this outlook issuance, there is little snow cover across a
large portion of central Illinois. However, snow depths of 2 to 3
inches were observed in northern counties within the ILX HSA,
including Stark, Marshall, and Woodford. The more significant
snowpack exists across southeastern sections of the HSA with the
latest observed snow depths of 4 to 6 inches. This includes Effingham
County eastward to Crawford County and south. Liquid equivalent of
the snow in these areas is generally less than 0.5 inch.

There is a storm system that will be bringing a mix of rain and/or
frozen precipitation to central and southern sections of Illinois
this weekend. There is still some uncertainty as to the amount of
rain that could fall across the south. However, any rain that does
fall in combination with the current snowpack would result in rising
river levels in some areas.


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 event in early February, this was all but
erased. The latest drought monitor from February 17th shows only very
small areas of DO in far northern and far southeastern 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 6 to 8 inches in depth. However, northernmost
areas were reporting frost depths of 10 to 13 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 streamflow conditions across central
Illinois are near normal for this time of year. There are even some
rivers in our southeast areas that are currently below normal levels.

With the recent sub-freezing temperatures, area rivers continue to
build ice. Ice buildup across the ILX Hydrologic Service Area has not
yet increased to the point where it is creating significant impacts.
However, with the continued cold temperatures we may get to the point
where it creates a greater threat for ice jams.


WEATHER OUTLOOKS...

After this weekend, the weather pattern across the Midwest will be
fairly quiet through the remainder of the month. The forecast over
this time period calls for temperatures below normal with highs
ranging in teens and low 20s and lows generally in the single digits.

The 8 to 14 day outlook (Feb 27th to Mar 5th) indicates a greater
than 50 percent likelihood for below normal temperatures across
Illinois with near normal precipitation.

The 30 day outlook for March indicates a greater than 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 minor flooding are forecast for the
Illinois River. This enhanced risk is largely being driven by
potential flow from upstream on the Illinois River from snowmelt. As
noted earlier in this outlook, the Chicagoland area received a
significant snowpack from the historic snowstorm in early February.
Melting of this snowpack in combination with any other precipitation
could contribute to higher streamflows along the Illinois River and
thus higher potential for at least minor flooding.

Near normal probabilities for flooding exist elsewhere across central
and southeast Illinois. The likelihood for minor flooding is highest
along the Little Wabash and portions of the Embarras River this
spring. However, these rivers typically experience at least minor
flooding this time of year. The main concern at this point is the
current snowpack of 4 to 6 inches in that area. With the frozen
ground, any appreciable warmup and/or rain event in the short term
could lead to an enhanced risk for flooding along those rivers.

Overall, any significant flooding across central and southeast
Illinois will be largely driven by spring rains or additional snow
and subsequent snowmelt. If temperatures remain cold with frost
depths at their current levels, then runoff potential will remain
high.

With the cold, also comes the potential threat of ice jams. These
threats are highly dependent on the weather conditions going forward
into the spring. Therefore, river ice conditions will continue to be
monitored over the coming weeks. Those people living along or near
rivers and streams should remain aware of the current conditions in
their area.


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:  2/23/2015 - 5/24/2015

                                       :    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 :  70   53   60   43   <5   <5
Peoria              18.0   22.0   28.0 :  83   63   33   27   <5   <5
Havana              14.0   17.0   23.0 :  84   69   47   41   <5   <5
Beardstown          14.0   18.0   28.0 :  87   80   67   56    6   <5
:Mackinaw River
Congerville 2NW     13.0   14.0   20.0 :  21   16   16   15   <5   <5
:Spoon River
London Mills        15.0   21.0   24.0 :  53   46   10    9   <5   <5
Seville             22.0   25.0   30.0 :  43   41   20   16   <5   <5
:Sangamon River
Monticello          13.0   17.0   20.0 :  58   63    6    6   <5   <5
Riverton            23.0   26.0   29.0 :  13   15   <5   <5   <5   <5
Petersburg          23.0   24.0   33.0 :  16   16   13   13   <5   <5
:Salt Creek
Greenview           16.0   17.0   20.0 :  16   23   13   13    7    7
:Sangamon River
Oakford            471.0  472.9  478.5 :  30   33   16   16   <5   <5
Chandlerville      456.6  459.0  462.0 :  43   49   18   20   <5   <5
:Little Wabash River
Clay City           18.0   22.0   25.0 :  94   <5   17   <5   <5   <5
:Vermilion River
Danville            18.0   22.0   28.0 :  18   <5    7   <5   <5   <5
:Embarras River
Lawrenceville       30.0   37.0   41.0 :  77   <5   16   <5   <5   <5
Ste. Marie          19.0   20.0   27.0 :  27   <5   19   <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: 2/23/2015 - 5/24/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Illinois River
Henry                19.2   20.3   22.6   24.5   26.2   27.5   30.0
Peoria               14.2   16.1   19.2   21.0   22.8   24.0   26.3
Havana               12.9   13.5   15.3   17.1   19.2   21.4   23.5
Beardstown           12.3   13.3   17.1   20.0   24.4   26.8   28.9
:Mackinaw River
Congerville 2NW       4.3    5.4    7.0   10.1   12.3   15.8   17.2
:Spoon River
London Mills          8.0   10.2   12.0   15.8   18.3   21.4   22.6
Seville              12.2   13.6   16.2   20.3   24.3   26.8   30.4
:Sangamon River
Monticello            9.3   10.1   12.0   13.2   14.4   15.6   17.6
Riverton             10.4   13.3   16.3   18.7   21.3   23.9   26.2
Petersburg            8.8   10.7   13.6   16.7   20.3   24.3   29.4
:Salt Creek
Greenview             4.5    6.3    8.0   11.4   14.2   19.2   21.4
:Sangamon River
Oakford             459.9  461.9  464.6  469.0  471.3  474.3  475.4
Chandlerville       447.3  449.4  452.2  456.4  458.2  460.8  461.7
:Little Wabash River
Clay City            15.6   18.3   19.7   20.5   21.4   22.7   23.5
:Vermilion River
Danville              8.3    8.6   10.9   14.2   16.3   20.4   24.1
:Embarras River
Lawrenceville        26.1   27.5   30.5   32.5   35.2   38.2   39.9
Ste. Marie            8.4    9.2   13.3   16.1   19.4   21.2   23.7

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: 2/23/2015 - 5/24/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Illinois River
Henry                14.8   14.7   14.7   14.7   14.7   14.6   14.5
Peoria               11.8   11.7   11.6   11.0   10.6   10.6   10.6
Havana                5.3    5.2    5.1    5.0    5.0    4.9    4.9
Beardstown            9.8    9.8    9.7    9.7    9.6    9.3    9.2
:Mackinaw River
Congerville 2NW       1.5    1.5    1.5    1.4    1.2    1.1    1.0
:Spoon River
London Mills          3.1    3.1    3.1    3.1    2.9    2.6    2.4
Seville               6.2    6.2    6.2    6.1    6.0    5.6    5.3
:Sangamon River
Monticello            7.0    6.9    6.8    6.5    6.3    5.8    5.7
Riverton              4.9    4.9    4.8    4.8    4.5    4.1    3.8
Petersburg            6.2    6.2    6.1    6.1    5.8    5.5    5.4
:Salt Creek
Greenview             1.9    1.9    1.8    1.7    1.5    1.2    1.1
:Sangamon River
Oakford             457.5  457.5  457.4  457.4  457.1  456.7  456.6
Chandlerville       444.8  444.8  444.7  444.7  444.4  444.0  443.9

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.

The next scheduled issuance of the Spring Flood and Water Resources
Outlook for central and southeast Illinois will be on Thursday, March
5th. 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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