National Weather Service United States Department of Commerce

2018 Spring Flood Outlook for Central and Southeast Illinois

Probabilistic Hydrologic Outlook
National Weather Service Lincoln IL
128 PM CST Thu Mar 01 2018

...2018 Spring Flood and Water Resources Outlook Number 2...

...Above normal potential for flooding along the Illinois River with
near normal potential 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 FOR CENTRAL AND SOUTHEAST IL...

- Risk of flooding this spring is above normal along the Illinois
  River and near normal elsewhere

- Locations that typically flood in the spring will have similar
  likelihood this season

- Flooding will be driven by springtime rains

- No current snowpack

- Current soil moisture near normal to slightly below normal

- No frost observed across the area (thawed soils)

- Current streamflows overall above normal to much above normal due
  to recent heavy rains

- Near normal temperatures across Illinois in early March, trending
  toward below normal mid-month

- Near normal precipitation across Illinois in early March, trending
  toward slightly wetter conditions mid-month


WINTER WEATHER REVIEW...

--December--

Information, courtesy of the Illinois State Climatologist, shows that
the mix of cold and warm weather in December more or less balanced
out, leaving the statewide average temperature for December at 30.4
degrees, 0.5 degrees above normal.

Looking at December, the statewide average precipitation total was
0.79 inches, 1.90 inches below normal and the 7th driest December on
record. Far southern Illinois received 1 to 3 inches of
precipitation, but the rest of the state received less than an inch.
Overall the state remained below normal on December snowfall. The
largest totals stretched from the Quad Cities and passed just south
of Chicagoland.

Across the ILX Hydrologic Service Area (HSA), monthly temperature
averages for December were near to below normal. They generally
ranged from 1.2 degrees below normal to 0.2 degrees above normal.
Daily high temperatures ranged from the single digits to the upper
60s. Normal highs for December range from the low 30s to the mid 40s.
Low temperatures across the area ranged from the single digits below
zero to the low 50s. They typically range from the teens to the upper
20s.

Monthly liquid precipitation for December was well below normal
overall across the ILX HSA. Monthly precipitation ranged from 0.12"
in Decatur to 2.62" in Mackinaw. These totals ranged from 2.42" to
0.08" below normal, respectively. This equates to precipitation that
roughly ranged from 5 percent to 97 percent of normal.

No river flooding was observed in the ILX HSA in December. U.S.
Geological Survey (USGS) streamflow values for December were overall
in the below normal to much below normal percentile range.

December Precipitation
(Accumulation)

December Precipitation
(Percent of Mean)

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

 

--January--

The Illinois State Climatologist notes that the statewide average
temperature for January was 24.1 degrees, 2.3 degrees below normal.
The month started with temperatures below zero and the month ended up
containing two unusually cold and unusually warm periods. The warmest
reading for the month was 68 degrees at Jerseyville on January 22.
The coldest reading for the month was -24 degrees at Morrison on
January 1.

Across the ILX HSA, monthly temperature averages for January averaged
below normal. They generally ranged from 0.5 degrees to 4 degrees
below normal. Daily high temperatures ranged from the single digits
below zero to the low 60s. Normal highs for January range into the
low to mid 30s. Low temperatures across the area ranged from the
teens below zero to the low 40s this month. They typically range into
the teens.

Liquid precipitation totals across the ILX HSA for January were well
below normal. Monthly precipitation ranged from 0.53" in Springfield
to 2.35" in Lawrenceville. These totals ranged from 1.29" to 0.03"
below normal, respectively. This equates to precipitation that
roughly ranged from 30 percent to near 100 percent of normal.

Due to the lack of appreciable precipitation, no river flooding was
observed across the ILX HSA in January. USGS monthly streamflows
showed overall below normal to much below normal values across most
of central and southern Illinois. However, the northern third of the
state saw streamflows near normal to above normal for the month.

January Precipitation
(Accumulation)

January Precipitation
(Percent of Mean)

January Snowfall
(Accumulation)
January Snowfall
(Percent of Mean)
 
Feb 18-24 Precipitation
(Accumulation)
 
Feb 18-24 Precipitation
(Percent of Mean)
 
-- February--

The month of February was a roller coaster with respect to
both temperatures and precipitation. The beginning of the 
month saw temperatures below normal. However, the second 
half saw above normal temperatures. Across the ILX HSA, 
monthly temperature averages for February came out above 
normal overall. They generally ranged from .5 to 3.5 
degrees above normal. Daily high temperatures ranged from 
the teens to over 70 degrees. Normal highs for February 
range into the mid 30s to mid 40s. Low temperatures across
the area ranged from around 10 degrees below zero to the 
mid 50s this month. They typically range from the teens 
to the upper 20s.

Again, the first half of the month saw below normal 
precipitation. However, the second half of February 
brought greater than normal precipitation. Overall, 
liquid precipitation totals across the ILX HSA were well
above normal for February. Monthly precipitation ranged
from 2.82" in Mattoon to 5.90" in Champaign. These 
totals ranged from 1.05" to 3.88" above normal, 
respectively. This equates to precipitation that 
roughly ranged from 150 percent to 300 percent of normal.

The heavy rain during the third week of the month pushed
many area rivers into flood. Rises along the Illinois 
River were significantly enhanced from upstream flow due
to a combination of rain and snow melt runoff. In 
addition to the Illinois River, central and southeast 
Illinois saw flooding along portions of the Spoon, 
Sangamon, Vermilion, Embarras, and Little Wabash rivers.

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)
12/1/17 - 2/28/18 12/1/17 - 2/28/18 12/1/17 - 2/28/18
SOIL MOISTURE AND FROST DEPTH CONDITIONS...

Soil moisture conditions across central and southeast Illinois are
near normal to slightly below normal. In addition, the warm
temperatures over the last two weeks have thoroughly thawed the soils
across the area.

Since no frost has been observed across central and southeast
Illinois, the recent heavy rains have been able to recharge the soils
across central and southeast Illinois. This has brought soil moisture
to overall near normal levels. Some slightly drier soils remain
across portions of west-central Illinois. However, those areas have
seen significant improvement. Locally, the soils may have some
additional capacity to hold water. However, any near-term heavy rains
could yield increased runoff as soils near saturation.

Across Illinois, drought conditions have significantly improved with
the recent heavy rains. In early December there was a large area of
D0 (Abnormally Dry) conditions across portions of central and
southwestern Illinois. Smaller areas of D0 were also seen across
east-central and southeast Illinois. Small areas of D1 (Moderate
Drought) and D2 (Severe Drought) were also observed in southwest
sections of the state.

The Drought Monitor from the February 15th release showed a large
expansion of D0 and D1 conditions since the beginning of the winter
season. D0 conditions had increased from 24 percent to 34 percent in
coverage across the state, while D1 conditions had increased from 3
percent to 24 percent. However, the latest Drought Monitor issuance
depicts a significant improvement over the last two weeks. Much of
the Illinois drought has been wiped out, except for an area of D0
conditions in west-central Illinois and a small area in the
northwest. D0 conditions now only cover a little more than 10 percent
of Illinois.


RIVER CONDITIONS...

Currently, there is minor to moderate river flooding occurring across
portions of the ILX HSA. The Illinois River from Henry to Beardstown
is in moderate flood...with minor flooding along portions of the
Little Wabash and Embarras Rivers. Information, courtesy of the U.S.
Geological Survey (USGS), shows that streamflow conditions across the
area are overall above normal to much above normal for this time of
year. Again, this is largely due to recent heavy rains across the
area in addition to upstream snowmelt, which has contributed to rises
along the Illinois River.

With the overall near normal temperatures forecast into early March,
any near-term precipitation that falls should largely be in the form
of rain. The weather pattern will be fairly quiet over the next two
weeks with only periodic chances for precipitation. We are not
anticipating any major rain events over this time period. This will,
thankfully, give elevated river levels time to come down. Going
forward, springtime heavy rains will be the primary driver for river
flooding across central and southeast Illinois.


WEATHER OUTLOOKS...

The overall weather pattern will be turning quieter as we head into
March. Dry conditions are expected across Illinois through weekend,
with the next chance for precipitation coming early next week. The
forecast for Illinois over the next week calls for overall near
normal temperatures with highs ranging mainly in the 40s and low 50s
and lows in the 30s.

The 8 to 14 day outlook (Mar 8 to Mar 14) indicates near normal
temperatures across the northern third of Illinois with greater than
33 percent likelihood for below normal temperatures across the
southern two-thirds. There is also near normal precipitation expected
across northeast Illinois with greater than 33 percent likelihood for
above normal precipitation over southwestern sections of the state
during this time period.

The 90 day outlook (March, April, and May) for Illinois indicates
that there are no strong signals for temperature. Therefore, equal
chances for below normal, normal, and above normal are outlined for
most of Illinois during this time period. Greater than 33 percent
likelihood for above normal precipitation exists for western
Illinois...increasing to 40 percent in the east over the next 90
days.


FLOOD OUTLOOK SUMMARY...

Near normal probabilities for flooding are forecast for central and
southeast Illinois this spring with the exception of the Illinois
River...which is above normal. The likelihood for flooding is highest
along portions of the Illinois, Embarras, and Little Wabash Rivers.
However, these locations typically experience at least minor flooding
during the spring.

Overall, any significant flooding across central and southeast
Illinois will be driven by springtime rains.

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

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:  03/11/2018 - 06/02/2018

                                       :    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 :  72   54   64   44   <5   <5
Peoria              18.0   22.0   28.0 : >95   62   41   28   <5   <5
Peoria L/D         447.0  449.0  455.0 : >95   52   53   34   <5   <5
Havana              14.0   17.0   23.0 : >95   68  >95   41    6   <5
:Mackinaw River
Congerville         13.0   14.0   20.0 :  17   17   13   14   <5   <5
:Spoon River
London Mills        15.0   21.0   24.0 :  52   51   15   10   <5   <5
Seville             22.0   25.0   30.0 :  41   42   25   19   <5   <5
:Sangamon River
Monticello          13.0   17.0   20.0 :  65   68    6    7   <5   <5
Riverton            23.0   26.0   29.0 :  13   14    6    5   <5   <5
Petersburg          23.0   24.0   33.0 :  15   15    9    7   <5   <5
:Salt Creek
Greenview           16.0   17.0   20.0 :  15   17   12   12    8    7
:Sangamon River
Oakford            471.0  472.9  478.5 :  26   31   15   15   <5   <5
Chandlerville      456.6  459.0  462.0 :  45   44   16   17   <5   <5
:Embarras River
Lawrenceville       30.0   37.0   41.0 :  69   72   16   17   <5   <5
Ste. Marie          19.0   20.0   27.0 :  31   35   22   23   <5   <5
:Little Wabash River
Clay City           18.0   22.0   25.0 :  83   83   17   19   <5   <5
:Vermilion River
Danville            18.0   22.0   28.0 :  20   24    8   15   <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: 03/11/2018 - 06/02/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Illinois River
Henry                21.5   21.6   22.6   24.9   26.4   27.4   29.2
Peoria               18.8   18.9   19.7   21.6   23.0   24.0   25.7
Peoria L/D          447.3  447.4  448.0  449.4  450.5  451.4  453.2
Havana               17.2   17.2   17.4   18.5   20.0   21.6   23.3
:Mackinaw River
Congerville           4.1    4.8    6.4    9.4   11.5   14.9   16.5
:Spoon River
London Mills          7.3    8.1   11.7   15.3   18.8   21.6   22.6
Seville              11.5   12.0   16.2   20.1   24.9   27.0   27.9
:Sangamon River
Monticello            9.8   10.7   12.4   13.6   15.0   16.4   17.4
Riverton             10.0   12.1   16.6   18.2   20.8   23.7   26.5
Petersburg            9.2    9.6   13.1   15.7   19.6   24.0   26.9
:Salt Creek
Greenview             5.2    6.3    9.0   11.3   13.6   18.3   21.5
:Sangamon River
Oakford             461.3  462.4  465.1  468.8  471.1  473.9  475.5
Chandlerville       448.8  449.8  452.7  456.2  458.1  460.5  461.8
:Embarras River
Lawrenceville        25.1   26.8   29.4   32.0   35.1   38.2   39.9
Ste. Marie            8.8    9.3   13.2   16.3   19.8   20.7   23.0
:Little Wabash River
Clay City            14.2   16.3   19.7   20.4   21.4   22.5   23.4
:Vermilion River
Danville              8.4    9.0   11.3   14.0   16.6   21.1   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: 03/11/2018 - 06/02/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Illinois River
Henry                15.5   15.4   15.2   15.0   14.8   14.7   14.5
Peoria               12.5   12.5   12.3   12.1   11.9   10.6   10.6
Peoria L/D          434.9  434.7  433.9  432.6  431.5  431.0  430.4
Havana                8.0    7.7    7.3    6.1    5.3    5.0    4.9
:Mackinaw River
Congerville           2.2    2.1    1.8    1.6    1.5    1.3    1.2
:Spoon River
London Mills          4.1    3.9    3.6    3.4    3.1    2.8    2.6
Seville               7.6    7.2    6.8    6.5    6.0    5.7    5.6
:Sangamon River
Monticello            7.9    7.5    7.1    6.8    6.4    6.1    6.0
Riverton              6.9    6.3    5.7    5.3    4.7    4.4    4.2
Petersburg            7.3    6.8    6.2    5.7    5.3    5.0    5.0
:Salt Creek
Greenview             2.8    2.5    2.1    1.9    1.6    1.4    1.3
:Sangamon River
Oakford             459.0  458.6  458.0  457.5  457.0  456.7  456.5
Chandlerville       446.3  445.9  445.2  444.8  444.3  443.9  443.8
:Embarras River
Lawrenceville        20.2   19.7   19.5   19.0   18.8   18.6   18.4
Ste. Marie            3.6    3.3    3.0    2.7    2.6    2.4    2.2
:Little Wabash River
Clay City             6.8    6.5    5.9    5.3    4.9    4.6    4.3
:Vermilion River
Danville              4.1    3.9    3.6    3.5    3.3    3.1    3.1

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 HSA.

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 last issuance of the 2018 Spring Flood and Water
Resources Outlook for central and southeast Illinois. The NOAA
National Spring Flood Outlook will be issued on Thursday, March 15th.
Flood Safety Awareness Week is March 12th to the 16th.

$$

 

NWS Lincoln Hydrologic Service Area

 

USGS Monthly Streamflows
(December 2017)




 


Drought Monitor
(Issued December 7, 2017)



 

USGS Monthly Streamflows
(January 2018)


 

Drought Monitor
(Issued January 4, 2018)



 

Drought Monitor
(Issued February 15, 2018)

 

USGS Daily Streamflow
(March 1, 2018)



 

Drought Monitor
(Issued March 1, 2018)

 

Frost Depth Conditions
(February 28, 2018)

 

CPC Soil Moisture Percentile Map


 

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)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Advanced Hydrologic Prediction Service (AHPS)


Climate Prediction Center (CPC)