National Weather Service United States Department of Commerce

2021 Spring Flood Outlook for Central and Southeast Illinois

Probabilistic Hydrologic Outlook
National Weather Service Lincoln IL
220 PM CST Thu Mar 11 2021

...2021 Spring Flood and Water Resources Outlook Number 3...

...Above normal likelihood for flooding along portions of the
Illinois, Sangamon, Little Wabash and Embarras rivers...

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 multi-season scenarios from more than 30
years of climatological data, current streamflows, soil conditions,
snow pack, as well as short/long range weather forecasts.

FLOOD OUTLOOK HIGHLIGHTS...

- Since the last outlook, probabilities for flooding have increased
along portions of the Illinois, Sangamon, Little Wabash, and Embarras
rivers. Near normal likelihood elsewhere across central and southeast
Illinois.

- Overall, flooding is expected to be minor with portions of the
Illinois River in the moderate flood category.

- Shallow soils continue to be on the wetter side from recent
snowmelt and rain over the last 24 hours. Deeper levels remains
relatively dry and able to take on some water tempering runoff in the
near term.

- Current streamflows are near normal to below normal across central
and southeast Illinois.

- Temperatures probabilities are expected to trend below normal over
the next week...transitioning to above normal for the remainder of
the month. Precipitation is expected to trend near normal to below
normal for the remainder of March.

- Springtime rains will drive our flood season going forward.


WINTER WEATHER REVIEW...

--December--

Statewide Temperatures/Precipitation:

Information, courtesy of the Illinois State Climatologist, shows
that December temperatures were much warmer than average across
Illinois...generally ranging from 1 to 6 degrees on the warm side.
Overall, the statewide average December temperature was 32.8
degrees, 2.9 degrees above the 30-year normal and tied for 35th
warmest on record for the state.

December total precipitation ranged from just under 3 inches in
northwest Illinois to just over 1 inch in much of central and
southern Illinois. The southern two-thirds of the state was drier
than average with deficits of between 2 and 3 inches in southern
Illinois.  Statewide total December precipitation was 1.78 inches,
approximately 0.91 inches below the 30-year normal and the 43rd
driest on record.

Most of the state experienced below normal snowfall in December. All
areas except the far northwest corner of Illinois had less than 5
inches of snowfall. These totals range between 1 and 10 inches below
average, with the largest departures in the Chicagoland area.

The December 29th issuance of the U.S. Drought Monitor showed
continued moderate drought across western and central Illinois, and
severe drought persisting along the I-72 corridor, between
Springfield and Decatur.

Local Temperatures/Precipitation:

Temperatures for December averaged well above normal across the ILX
Hydrologic Service Area (HSA). They generally ranged from 2 to 4
degrees above normal. Daily high temperatures ranged from the upper
teens to the mid-60s. Normal highs for December typically range from
the low 30s to the mid-40s. Low temperatures across the area ranged
from the single digits to the low 40s in December. They typically
range from the teens to the upper 20s.

Liquid precipitation totals across the ILX HSA were below normal.
Monthly precipitation ranged from 0.72 inches in Yates City to 2.72
inches in Paris. These totals ranged from 1.31 to 0.31 inches below
normal, respectively. This equates to precipitation that roughly
ranged from 35 to 90 percent of normal.

With the below normal precipitation, central and southeast Illinois
did not experience any flooding during the month of January.

U.S. Geological Survey (USGS) monthly average streamflow values for
December were in the normal range across most of Illinois. The main
exception was across portions central Illinois, where streamflows
were in the below normal...to much below normal category for the
month.

 

December Precipitation
(Accumulation)

December Precipitation
(Percent of Mean)

December Snowfall
(Accumulation)
December Snowfall
(Percent of Mean)
--January--

Statewide Temperatures/Precipitation:

The Illinois State Climatologist notes that our first month of 2021
was quite a bit warmer than average across the state. The
preliminary statewide average January temperature was 28.8 degrees,
2.4 degrees above the 1981-2010 normal and tied for the 36th warmest
on record going back to 1895.

Climatologically, January is one of the drier months of the year in
Illinois. This year, it started with rain and snow for most of the
state, followed by two weeks when most of the state received less
than half an inch of total precipitation. However, the last week of
January brought more active winter weather, including multiple large
winter storms that produced heavy precipitation and impressive snow
totals across the state.

January total snowfall ranged from less than half an inch in
southern Illinois to over 20 inches in northern Illinois. Total
snowfall is 10 to 50 percent of average in southern and central
Illinois and above average only in northwest and far northern
Illinois.

Overall, total January precipitation ranged from nearly 6 inches in
far southern Illinois to just under 2 inches in northwest Illinois.
Preliminary statewide average total January precipitation was 2.56
inches, 0.49 inches above normal and tied for the 32nd wettest on
record.

Local Temperatures/Precipitation:

Temperatures for January continued the warm trend and also averaged
above normal across the ILX Hydrologic Service Area (HSA). They
generally ranged from 2 to 4 degrees above normal. Daily high
temperatures ranged from the mid-20s to the mid-50s. Normal highs
for January range into the low to mid-30s. Low temperatures across
the area ranged from the single digits to the mid-30s this month.
They typically range into the teens.

Liquid precipitation totals across the ILX HSA were overall above
normal. Monthly precipitation ranged from 1.27 inches in Hoopeston
to 3.42 inches in Lincoln. These totals ranged from 0.49 inches
below normal to 1.49 inches above normal, respectively. This equates
to precipitation that roughly ranged from 70 to 175 percent of
normal.

Only minor river flooding was observed in our southeast HSA, along
the Little Wabash River below Clay City. Flooding occurred in early
January, and again in late January to early February.

USGS monthly average streamflow values for January largely remained
in the normal range across most of Illinois. Portions of central
Illinois, continued to have streamflows that were in the below
normal...to much below normal range.

 

January Precipitation
(Accumulation)

January Precipitation
(Percent of Mean)

January Snowfall
(Accumulation)
January Snowfall
(Percent of Mean)
--February--

Information, courtesy of the Illinois State Climatologist, shows the
statewide average February temperature was 20.0 degrees, 11.1 degrees
below normal and 10th coldest on record going back to 1895. February
propelled the 2020-21 winter season temperatures into below normal
territory, despite a warmer than normal January and December. Winter
average temperatures ranged from the high teens in northern Illinois
to the high 30s in southern Illinois, between 0 and 4 degrees below
normal.

February was noteworthy not only for extremely cold weather, but also
for exceedingly high snowfall totals. The position of the subpolar
jet stream created an active winter storm track across the state,
bringing multiple heavy snowfall events. One storm in particular
produced 10 to 20 inches of snow in a 24-hour period in the northeast
part of the state. February snowfall totals ranged from just under 34
inches in the northern Chicago suburbs to about 3 inches in Mt.
Vernon.

Because February snow fell from very cold air, it did not produce a
large amount of equivalent liquid precipitation. February total
precipitation ranged from just over an inch in far northern Illinois
to just over six inches in southeast Illinois. All areas except for
the southeast quadrant were a tenth to one inch drier than normal.
Combined with drier than average months in January and December, most
parts of the state experienced a winter season that was one-half inch
to three inches drier than normal.

Overall, statewide average total precipitation was 2.01 inches in
February, 0.10 inches below normal and tied for the 51st wettest on
record going back to 1895.

Local Temperatures/Precipitation:

Temperatures for February averaged 8 to 10 degrees below normal
across the ILX Hydrologic Service Area (HSA). Daily high temperatures
ranged from the single digits to the mid-60s. Normal highs for
February range into the mid-30s to the mid-40s. Low temperatures
across the area ranged from the single digits below zero to the mid-
40s this month. They typically range from the teens to the upper 20s.

Liquid precipitation totals across the ILX HSA were a mixed bag.
Monthly precipitation ranged from 1.03 inches in Minonk to 4.42
inches in Flora. These totals ranged from 0.93 inches below normal to
1.78 inches above normal, respectively. This equates to precipitation
that roughly ranged from 55 to 165 percent of normal.

Snowfall totals were above normal for February. They ranged from 6.6
inches in Pana to 18.6 inches in Lawrenceville. These totals ranged
from 2.0 inches to 14.1 inches above normal, respectively.

Only minor flooding was observed along the Little Wabash River below
Clay City toward the end of February, but that only lasted a few
days.

 

February Precipitation
(Accumulation)

February Precipitation
(Percent of Mean)

February Snowfall
(Accumulation)
February Snowfall
(Percent of Mean)

 

Winter Precipitation Winter Snowfall Average Temperature
(Percent of Mean) (Percent of Mean) (Departure from Mean)
--March--

The month of March, to this point, has seen above normal
temperatures...ranging from around 5 to 10 degrees above normal
across the ILX Hydrologic Service Area (HSA).

Liquid precipitation, thus far, has averaged below normal...amounting
to no more than trace amounts. This is around 0.50 to 0.80 inches
below normal this far into March.

As of this issuance there is no flooding occurring across central and
southeast Illinois. However, the precipitation over the next few days
will likely cause river levels to rise across the state, especially
across the southern half.


SOIL MOISTURE AND FROST DEPTH CONDITIONS...

Soil moisture conditions across most of Illinois are normal to below
normal for this time of year. Thankfully, there is no longer any
frost across central and southeast Illinois. Although shallow soils
have been on the wetter side, the deeper layers are relatively dry
which will help temper runoff potential early on.

Drought conditions in Illinois have been fairly consistent through
the winter season, with only modest evolution over the past few
months. As of the latest Drought Monitor issuance, D0 (Abnormally
Dry) conditions expand across portions of central and east-central
Illinois, covering a little under 20 percent of the state. D1
(Moderate Drought) conditions extended across portions of east-
central Illinois, covering less than 5 percent of the state.


RIVER CONDITIONS...

As of this issuance, there is no flooding occurring across central
and southeast Illinois. Information, courtesy of the U.S. Geological
Survey (USGS), shows that streamflows across central and southeast
Illinois are currently in the normal to below normal range for this
time of year. However, flows are expected to increase over the next
several days as we enter a period of unsettled weather, especially
across southern Illinois.

With the warming temperatures over the past couple of weeks, rivers
should largely be flowing ice-free. Therefore, concerns for ice jam
potential have really dropped off.


WEATHER OUTLOOKS...

The weather pattern into early next week will be rather unsettled
with periodic chances for rain. Temperatures are expected to
transition from above normal to below normal as we head into next
week with highs dropping to the mid to upper 40s.

The 8 to 14 day outlook (Mar 18 to Mar 24) indicates a greater than
33 percent likelihood for above normal temperatures across
Illinois...increasing to greater than 40 percent in far northern
sections of the state. There is a greater than 33 percent likelihood
for below normal precipitation throughout the Illinois during this
period.

The outlook for this spring (March, April, and May) indicates a
greater than 33 percent likelihood for above normal temperatures
across Illinois...increasing to greater than 40 across the southern
third of the state. There is also a greater than 33 percent
likelihood for above normal precipitation...increasing to greater
than 40 likelihood in east-central and northeast Illinois.

The signal for above normal precipitation this spring is largely
focused across the Great Lakes and Ohio River Valley. This is what we
would expect as we transition out of La Nina conditions...trending
toward ENSO-neutral conditions this summer and fall.


FLOOD OUTLOOK SUMMARY...

Since the last outlook, probabilities for flooding have increased
along portions of the Illinois, Sangamon, Little Wabash, and Embarras
rivers. Near normal likelihood for flooding is expected elsewhere
across central and southeast Illinois.

Overall, flooding this spring is expected to be in the minor category
with moderate flooding along portions of the Illinois River.
Springtime rains will be the driving factor for how this flood season
unfolds. If we get a significantly wet spring season then we could
see more areas with moderate flooding.

Currently, we are not experiencing any river flooding across central
and southeast Illinois. Streamflows are in the normal to below normal
range. However, the periodic rain chances over the next several days
are expected to increase flows across the state, especially across
southern Illinois.

The warm temperatures over the past few weeks have allowed frozen
soils to completely thaw. Overall soil moisture levels are near
normal to below normal. Though the shallow soils may be on the wetter
side, deeper soils are relatively dry. Therefore, this increased
storage capacity in the soils should help temper runoff early this
season until reaching saturation.

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

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:  03/15/2021 - 06/13/2021

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Illinois River
Henry               23.0   24.0   31.0 :  78   54   47   46   <5   <5
Peoria              18.0   22.0   28.0 : >95   63   28   31   <5   <5
Peoria L/D         447.0  449.0  455.0 :  85   54   32   34   <5   <5
Havana              14.0   17.0   23.0 : >95   84  >95   60   15   18
Beardstown          14.0   18.0   28.0 : >95   79  >95   54   <5    5
:Mackinaw River
Congerville         13.0   14.0   20.0 :  22   19   15   15   <5   <5
:Spoon River
London Mills        15.0   21.0   24.0 :  48   45    6   <5   <5   <5
Seville             22.0   25.0   30.0 :  39   39   22   16   <5   <5
:Sangamon River
Monticello          13.0   17.0   20.0 : >95   69    7    8   <5   <5
Riverton            23.0   26.0   29.0 :  11   11   <5   <5   <5   <5
Petersburg          23.0   24.0   33.0 :  24   25   19   17   <5   <5
:Salt Creek
Greenview           16.0   17.0   20.0 :  16   17   13   11    6   <5
:Sangamon River
Oakford            471.0  472.9  478.5 :  42   35   18   20   <5   <5
Chandlerville      456.6  459.0  462.0 :  76   47   24   21   <5   <5
:Embarras River
Lawrenceville       30.0   37.0   41.0 :  68   71   18   17   <5   <5
Ste. Marie          19.0   20.0   27.0 :  41   31   30   23   <5   <5
:Little Wabash River
Clay City           18.0   22.0   25.0 :  93   82   25   19   <5   <5
:Vermilion River
Danville            18.0   22.0   28.0 :  19   26    8   14   <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: 03/15/2021 - 06/13/2021
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Illinois River
Henry                22.9   22.9   23.1   23.8   25.8   27.1   28.2
Peoria               19.4   19.4   19.6   20.3   22.2   23.9   24.8
Peoria L/D          446.9  446.9  447.1  447.8  449.8  451.2  452.1
Havana               18.1   18.1   18.5   19.4   21.4   23.8   26.2
Beardstown           19.5   19.6   20.1   21.9   24.5   26.7   27.9
:Mackinaw River
Congerville           8.5    8.6    8.6    9.9   12.1   15.9   16.7
:Spoon River
London Mills         11.9   11.9   12.2   14.7   18.6   20.3   22.4
Seville              18.3   18.3   18.4   19.7   24.6   26.4   29.5
:Sangamon River
Monticello           13.8   13.8   13.8   13.9   15.0   16.4   17.6
Riverton             18.8   18.8   19.0   19.7   21.6   23.7   25.7
Petersburg           17.6   17.6   17.9   19.4   22.2   26.1   27.3
:Salt Creek
Greenview            11.2   11.2   11.2   11.6   13.5   17.4   20.6
:Sangamon River
Oakford             469.2  469.2  469.4  470.8  472.0  473.9  475.7
Chandlerville       456.4  456.4  456.6  457.7  458.8  460.5  461.9
:Embarras River
Lawrenceville        26.2   27.2   28.9   32.6   35.3   38.9   40.3
Ste. Marie            9.8   11.4   14.8   18.2   20.4   22.1   23.6
:Little Wabash River
Clay City            17.6   18.6   20.3   21.1   21.9   23.9   24.9
:Vermilion River
Danville              7.5    8.1   10.0   12.8   16.2   20.7   23.4

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: 03/15/2021 - 06/13/2021
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Illinois River
Henry                15.3   15.2   15.0   14.9   14.7   14.4   14.3
Peoria               12.4   12.3   12.1   12.0   11.0   10.6   10.6
Peoria L/D          434.6  433.7  433.0  432.0  431.1  430.3  430.1
Havana                7.9    7.3    6.3    5.6    5.0    4.9    4.8
Beardstown           10.7   10.5   10.2    9.9    9.6    9.2    9.1
:Mackinaw River
Congerville           2.3    2.2    1.9    1.9    1.7    1.6    1.5
:Spoon River
London Mills          4.0    3.9    3.5    3.0    2.6    2.4    2.4
Seville               7.6    7.4    6.9    6.4    6.0    5.7    5.6
:Sangamon River
Monticello            7.4    7.1    6.7    6.4    6.0    5.7    5.5
Riverton              7.1    6.7    5.9    5.0    4.4    4.0    3.9
Petersburg            7.3    7.1    6.4    5.8    5.4    5.3    5.2
:Salt Creek
Greenview             2.4    2.2    1.8    1.6    1.3    1.1    1.0
:Sangamon River
Oakford             459.0  458.7  458.0  457.5  457.0  456.7  456.6
Chandlerville       446.3  446.0  445.3  444.8  444.3  444.0  443.9
:Embarras River
Lawrenceville        19.2   19.0   18.6   18.2   17.9   17.7   17.5
Ste. Marie            3.5    3.3    2.9    2.5    2.2    1.9    1.8
:Little Wabash River
Clay City             7.1    6.6    5.8    5.3    4.7    4.4    4.1
:Vermilion River
Danville              3.5    3.4    3.1    2.9    2.7    2.5    2.4

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.

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

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 along the top menu
bar. Full AHPS graphics are available for all forecast points in the
ILX Hydrologic Service Area.

For 30 to 90 day temperature and precipitation outlooks, visit the
web page of the Climate Prediction Center at www.cpc.ncep.noaa.gov.
This will be the final issuance of the 2021 Spring Flood Outlook for
central and southeast Illinois. The NOAA National Spring Flood
Outlook will be issued on Thursday, March 18th. Visit our web site
weather.gov/ilx for more weather and water information.

 

NWS Lincoln Hydrologic Service Area

 

USGS Monthly Streamflow
(December 2020)




 


Drought Monitor
(Issued December 1, 2020)



 

USGS Monthly Streamflow
(January 2021)


 

Drought Monitor
(Issued January 5, 2021)



 

USGS Monthly Streamflow
(February 2021)

 

Drought Monitor
(Issued February 23, 2021)

 

USGS Daily Streamflow
(March 8, 2021)



 

Drought Monitor
(Issued March 9, 2021)

 

 

Frost Depth Conditions
(February 11, 2021)


 

CPC Soil Moisture Percentile Map

 

Modeled Snow Depth
Mar 11, 2021
 
Modeled Snow Depth - Departure from Normal
Mar 11, 2021

 
Modeled Snow Water Equivalent (SWE)
Mar 11, 2021
 
NCRFC Ranked Simulated SWE
Mar 8, 2021
 
 
Spring Leaf Index Anomaly Map

 

Extended Range Outlooks

6-10 Day Temperature Outlook 6-10 Day Precipitation Outlook
   
8-14 Day Temperature Outlook 8-14 Day Precipitation Outlook
   

One Month Temperature Outlook (Mar) One Month Precipitation Outlook (Mar)
   

Three Month Temperature Outlook (Mar-May) Three Month Precipitation Outlook (Mar-May)

 

Greater than 50% chance
of exceeding river flood levels (FEB/MAR/APR)

 

Greater than 75% chance
of exceeding river flood levels (FEB/MAR/APR)

 

Greater than 95% chance
of exceeding river flood levels (FEB/MAR/APR)

 

Advanced Hydrologic Prediction Service (AHPS)


Climate Prediction Center (CPC)