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2020 Spring Flood Outlook for Central and Southeast Illinois

Probabilistic Hydrologic Outlook
National Weather Service Lincoln IL
1255 PM CDT Thu Mar 12 2020

...2020 Spring Flood and Water Resources Outlook Number 3...

...Above normal potential for flooding this spring along portions of
the Illinois, Embarras, and Little Wabash rivers with near normal
likelihood across the remainder of 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 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...

- Above normal likelihood for flooding this spring along portions of
the Illinois, Embarras, and Little Wabash rivers...near normal across
the remainder of central and southeast Illinois.

- Those locations that typically flood in the spring will have
similar likelihood this season.

- Current soil moisture greater than 95th percentile is a concern
for runoff.

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

- Above normal temperatures favored across Illinois with above normal
precipitation favored across the southern half of the state in March.

- Any significant flooding will be primarily driven by spring rains.


WINTER WEATHER REVIEW...

--December--

Statewide Temperatures/Precipitation:

Information, courtesy of the Illinois State Climatologist, shows
that December temperatures were well above the long-term average
across Illinois, breaking dozens of local daily maximum and minimum
temperature records. The statewide December average temperature was
35.2 degrees, about 5 degrees above normal and the 18th warmest on
record. December was drier than average for most of the state. The
statewide average precipitation total was 2.03 inches, 0.66 inches
below the 30-year normal.

Temperatures during the first half of December were very close to
average. This was followed by a brief period of well below average
temperatures. On December 20th, southwesterly flow brought warm, dry
air into the region. Temperatures between December 20 and 29 ranged
from 5 to 25 degrees above normal across the state. In total, 104
daily high maximum temperature records and 27 daily high minimum
temperature records were broken over this time period, including a
few dozen records on December 25. In fact, it was the warmest
Christmas day at 68 stations across the state.

A shift in the upper atmosphere and the passage of a cold front late
in the month allowed temperatures to moderate. December average
temperatures ranged from the low 30s in northern Illinois to the
mid-40s in southern Illinois. Monthly average temperature departures
ranged from 7 degrees above the long-term mean in northwestern
Illinois to just over 1 degree above average in south-central
Illinois.

December precipitation was below the long-term average for the
entire state. Areas in far southern Illinois received 2 to 3 inches
less than average in December, approximately 50 percent of normal
December precipitation. The statewide average total precipitation
was 2.03 inches, approximately 0.66 inches below normal for the
month. This was the 50th driest December on record in Illinois and
marked the second straight month of below average statewide
precipitation. Preexisting wetness and reduced evaporative demand,
typical for this time of the year, prevented impacts from the
prolonged dry conditions.

December snowfall totals ranged from less than a tenth of an inch in
far southern Illinois to over 10 inches in south-central Illinois. A
strong system came through mid-month and brought several inches of
snow to an area spanning the St. Louis Metro East to the Champaign-
Urbana area. The December snowfall glut in south-central Illinois
turned into snowfall deficits of 8 to 10 inches in northern Illinois.

Local Temperatures/Precipitation:

Temperatures for December averaged well above normal across the ILX
Hydrologic Service Area (HSA). They generally ranged from 3 to 6
degrees above normal. Daily high temperatures ranged from the mid-
20s to the upper 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 50s 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 0.75 inches in Champaign to 3.36
inches in Olney. These totals ranged from 1.77 to 0.52 inches below
normal, respectively. This equates to precipitation that ranged from
30 to 87 percent of normal.

Minor flooding was observed across portions of the Little Wabash and
Embarras Rivers. However, this came to an end the first week of
December. Renewed flooding along the Little Wabash River came at the
very end of the month and continued into January.

U.S. Geological Survey (USGS) monthly average streamflow values for
December were in the normal to above normal range overall across
most of the state. The main exceptions were in northwest Illinois
and along portions of the Mississippi River, where streamflows were
much above normal 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 2020
was quite a bit warmer and wetter than average across the state. The
statewide average January temperature was 31.4 degrees, 5 degrees
above the 30-year normal and the 17th warmest on record going back
to 1895. The statewide average total January precipitation was 4.41
inches, 2.34 inches above the 30-year normal and the 9th wettest on
record.

Following a warmer than average December, temperatures remained
persistently above average for the first half of January, with only
a short cold air incursion between Jan. 15 and 23. January average
temperatures ranged from the mid-20s in northern Illinois to the
high 30s in southern Illinois, and were 2 to 7 degrees above average
across the state.

January total precipitation was above normal across the state, with
monthly precipitation totals ranging from 2 inches in northwestern
Illinois to nearly 8 inches in south-central Illinois. The highest
accumulation was along the Interstate 70 corridor between the St.
Louis Metro East and Effingham. This region experienced nearly 300
percent of its average January total precipitation. As with most of
the wettest parts of the state, most of the January precipitation
fell in just three days. Much of this was the result of a single
winter storm that moved through the Midwest between the 9th and
12th.

Snowfall totals in January ranged from less than a tenth of an inch
in southern Illinois to over 12 inches in northwestern Illinois.
There was a strong southeast-to-northwest January snowfall gradient
across the state, resulting from a similar gradient in air
temperature. The highest monthly snowfall total was 15 inches in
both Stephenson and Bureau Counties. Rockford experienced the
highest 1-day snowfall maximum across the state with 6 inches on
Jan. 25.

Local Temperatures/Precipitation:

Temperatures for January averaged well above normal across the ILX
Hydrologic Service Area (HSA). They generally ranged from 5 to 7
degrees above normal. Daily high temperatures ranged from the low
teens to the low 60s. Normal highs for January range into the low to
mid 30s. Low temperatures across the area ranged from the single
digits to the low 50s this month. They typically range into the
teens.

Liquid precipitation totals across the ILX HSA were well above
normal. Monthly precipitation ranged from 2.58 inches in Galesburg to
7.59 inches in Beecher City. These totals ranged from 1.07 to 5.09
inches above normal, respectively. This equates to precipitation that
roughly ranged from 170 to 300 percent of normal.

There was more widespread river flooding across central and southeast
Illinois than had been seen in recent months. We saw minor
flooding along portions of the Illinois, Sangamon, Little Wabash and
Embarras rivers. However, many other locations saw rises to near-
flood levels.

USGS monthly average streamflow values for January reflected the
above normal precipitation. Overall, values ranged from above normal
to much above normal throughout the state.

January Precipitation
(Accumulation)

January Precipitation
(Percent of Mean)

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

Statewide Temperatures/Precipitation:

The Illinois State Climatologist notes that February was slightly
warmer and wetter than average across Illinois, bringing an end to a
very warm winter season. The statewide average temperature was 31.2
degrees, 0.30 degrees above the 30-year normal and tied for 42nd
warmest on record. Statewide average total precipitation for February
was 2.13 inches, 0.07 inches wetter than the 30-year normal and tied
for 46th wettest on record.

February started consistently warmer than average, but multiple cold
air incursions in the latter half of the month led to an overall
near-normal temperature month. Average temperatures in February
ranged from the high teens in northwestern Illinois to the high 30s
in southern Illinois. Average temperatures ranged within a degree of
the long-term average for all but a southeast sliver of the state.

The warm weather that started the month resulted in 115 daily high
maximum temperature records and 12 daily high minimum records being
broken across the state. One truly incredible departure was a 70
degree high temperature in Charleston in Coles County on Feb. 3rd.
This was nearly twice the long-term average daily high temperature of
38 degrees for that calendar day in Charleston and 5 degrees above
the previous record. Eleven days later the Charleston station broke
its daily low maximum temperature, reaching only 15 degrees on
Valentine`s Day. In total, there were 23 daily low maximum
temperature records and 34 daily low minimum temperature records
being broken, most of which were recorded on Valentine`s Day.

The highest temperature recorded in the state in February was 72
degrees in Effingham County, while the lowest temperature was -18
degrees in Jo Daviess County.

In February, storms tended to track south of the state, bringing the
most rain to southern and south-central portions of Illinois. Total
February precipitation ranged from over 10 inches in far southern
Illinois to just over a tenth of an inch in northwestern Illinois.
These totals range from over 150 percent of average February
precipitation in southern Illinois to less than 25 percent of average
in northern Illinois.

While southern Illinois was experiencing persistent rain, most of
northern Illinois was treated to abundant snowfall. Snowfall totals
from February ranged from just over 15 inches in Kane County to less
than an inch along Interstate 70. Thanks to a mid-month storm, a
small area of Mason, Cass, and Menard counties received 6 to 8 inches
more than average snowfall in February, whereas most of the rest of
the state north of Interstate 70 received near average to just a
couple of inches above average snowfall.

Local Temperatures/Precipitation:

Temperatures for February averaged above normal across the ILX
Hydrologic Service Area (HSA). They generally ranged from 0.5 to 1.5
degrees above normal. Daily high temperatures ranged from the single
digits to the low 70s. Normal highs for February range into the mid
30s to mid 40s. Low temperatures across the area ranged from the
single digits below zero to the upper 40s. They typically range from
the teens to the upper 20s.

Liquid precipitation totals across the ILX HSA were above normal
overall. However, a few locations received below normal precipitation
in February. Monthly precipitation ranged from 1.37 inches in Minonk
to 3.63 inches in Palestine. These totals ranged from 0.59 inches
below normal to 1.07 inches above normal, respectively. This equates
to precipitation that roughly ranged from 70 to 140 percent of
normal.

Flooding in February was mainly contained to portions of the
Illinois, Embarras and Little Wabash Rivers. These locations saw only
minor flooding.

USGS monthly average streamflow values for February were overall near
normal to above normal throughout the state. However, well above
normal streamflows were observed along the Mississippi River from St.
Louis to areas downstream as well as portions of the Kaskaskia River
and Spring Creek.

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)
SOIL MOISTURE AND FROST DEPTH CONDITIONS...

Soil moisture conditions across Illinois remain well above normal...
and greater than the 95th percentile for this time of year. As such,
drought conditions in Illinois are not currently a concern and have
been non-existent since November 2019. As of the latest Drought
Monitor issuance, there continues to be no drought conditions noted
in Illinois.

The longer duration of above normal temperatures and minimal snowpack
has resulted no frost across central and southeast Illinois for the
last several weeks. As a matter of fact, there currently is no frost
up through southern Wisconsin.

As we continue through spring, the saturated soils will be a
significant contributing factor to flood potential. However, thawed
soils are of benefit, if optimal conditions allow for some drying.
Temperature outlooks over the next 2 weeks continue to favor near
normal to above normal temperatures. However, precipitation outlooks
favor above normal precipitation...especially across central and
southern Illinois. Therefore, significant drying is not likely to
occur in the short term.

RIVER CONDITIONS...

As mentioned, there is only minor flooding occurring along the
Illinois River at Beardstown and Little Wabash River near Clay City.
Otherwise, central and southern Illinois are flood-free as of this
Spring Flood Outlook issuance.

Information, courtesy of the U.S. Geological Survey (USGS), shows
above normal to much above normal streamflows across far northern
Illinois as well as western sections of the state. Streamflows across
the remainder of the state are in the normal to above normal range.

There will be several chances for rain over the next week. The
heaviest rains currently look to impact central and southern Illinois
most significantly. With high soil moisture in place, much of the
rain will likely go towards runoff. As a result, rising river levels
and flooding concerns will be in play.

WEATHER OUTLOOKS...

The latest forecast for Illinois calls for near normal temperatures
through this weekend, then above normal temperatures as we head into
next week. Multiple rounds of rain will impact Illinois. However the
primary focus will be central and southern sections of the state,
where the heaviest precipitation is forecast. Current expectations
are for rainfall amounts to range from 1 to 1.5 inches in central
Illinois...to 2 to 3 inches across southern sections of the state.

The 8 to 14 day outlook (Mar 19th - 25th) indicates overall near
normal temperatures across most of Illinois. Above normal
precipitation is currently favored for this time period across the
state, but is more likely across the southeastern half of Illinois.

The latest outlook for this spring (March, April, and May) indicates
a lot of uncertainty for temperatures across Illinois...with no
favored trends. However, there is a greater than 40 percent
likelihood for above normal precipitation outlined across Illinois.

FLOOD OUTLOOK SUMMARY...

Probabilities for flooding this spring are overall near normal
across central and southeast Illinois. The exceptions are for
portions of the Illinois, Embarras, and Little Wabash rivers...where
probabilities are higher than normal. However, these rivers typically
experience at least minor flooding in the spring.

For central and southeast Illinois, springtime rains will be the
driving factor in the evolution of this year`s flood season. The
saturated soil conditions and elevated streamflows will likely reduce
the response time of local rivers and streams, due to efficient
runoff. In turn, this would reduce the response time for people
living in these areas...should flooding occur. We are currently not
expecting widespread flooding across central and southeast Illinois.
However, if we trend toward a very wet spring, then more widespread
flooding will be possible.

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

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:  03/16/2020 - 06/14/2020

                                       :    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 :  54   53   38   43   <5   <5
Peoria              18.0   22.0   28.0 :  67   63   23   27   <5   <5
Peoria L/D         447.0  449.0  455.0 :  52   53   27   32   <5   <5
Havana              14.0   17.0   23.0 :  73   69   37   41   <5   <5
Beardstown          14.0   18.0   28.0 : >95   79   63   56   <5   <5
:Mackinaw River
Congerville         13.0   14.0   20.0 :  19   17   15   15   <5   <5
:Spoon River
London Mills        15.0   21.0   24.0 :  47   49   <5   <5   <5   <5
Seville             22.0   25.0   30.0 :  37   42   19   15   <5   <5
:Sangamon River
Monticello          13.0   17.0   20.0 :  67   66    7    7   <5   <5
Riverton            23.0   26.0   29.0 :  14   12    5   <5   <5   <5
Petersburg          23.0   24.0   33.0 :  21   20   19   18   <5   <5
:Salt Creek
Greenview           16.0   17.0   20.0 :  16   17   11   10    7   <5
:Sangamon River
Oakford            471.0  472.9  478.5 :  34   36   17   18   <5   <5
Chandlerville      456.6  459.0  462.0 :  48   47   20   20   <5   <5
:Embarras River
Lawrenceville       30.0   37.0   41.0 :  75   71   17   17   <5   <5
Ste. Marie          19.0   20.0   27.0 :  51   31   32   23   <5   <5
:Little Wabash River
Clay City           18.0   22.0   25.0 :  92   82   25   19   <5   <5
:Vermilion River
Danville            18.0   22.0   28.0 :  28   29   12   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: 03/16/2020 - 06/14/2020
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Illinois River
Henry                17.4   18.3   20.0   23.3   25.2   26.7   27.2
Peoria               13.6   13.8   16.2   19.7   21.9   23.0   23.7
Peoria L/D          440.4  441.0  443.7  447.1  449.4  450.4  451.0
Havana               12.9   13.1   13.8   16.2   18.4   20.1   20.8
Beardstown           14.7   14.8   16.7   19.1   23.3   25.5   27.3
:Mackinaw River
Congerville           5.2    5.6    6.8    9.5   12.4   15.2   17.0
:Spoon River
London Mills          7.1    8.4   11.0   14.2   18.3   20.1   21.0
Seville              11.7   12.6   15.7   19.1   24.2   26.1   27.1
:Sangamon River
Monticello           11.9   12.0   12.7   13.7   15.0   16.5   17.9
Riverton             16.7   16.7   17.0   18.9   21.5   23.8   26.1
Petersburg           14.3   14.3   14.9   17.3   21.8   25.8   28.3
:Salt Creek
Greenview             7.2    7.2    8.8   11.0   13.3   17.6   20.8
:Sangamon River
Oakford             465.7  465.8  466.8  469.1  471.8  474.1  475.6
Chandlerville       453.4  453.4  454.4  456.3  458.6  460.7  461.9
:Embarras River
Lawrenceville        27.3   27.6   30.0   33.7   35.3   38.7   41.0
Ste. Marie           10.8   11.7   14.2   19.1   20.4   21.8   22.7
:Little Wabash River
Clay City            17.5   18.5   20.1   21.0   22.0   24.1   24.8
:Vermilion River
Danville              8.4    9.3   11.1   14.4   18.6   22.7   24.2

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--Nonexceedance Probabilities...

                            Chance of Falling Below Stages
                                 at Specific Locations
                          Valid Period: 03/16/2020 - 06/14/2020
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Illinois River
Henry                15.3   15.2   15.0   14.9   14.7   14.4   14.4
Peoria               12.4   12.3   12.1   11.9   10.7   10.6   10.6
Peoria L/D          434.2  433.8  432.6  431.9  431.1  430.3  430.2
Havana                7.6    7.4    6.3    5.6    5.0    4.9    4.8
Beardstown           10.7   10.5   10.1    9.9    9.6    9.2    9.1
:Mackinaw River
Congerville           1.9    1.8    1.5    1.4    1.2    1.1    1.0
:Spoon River
London Mills          4.0    3.6    3.3    2.9    2.6    2.3    2.2
Seville               7.3    6.9    6.5    6.1    5.7    5.4    5.1
:Sangamon River
Monticello            7.2    7.0    6.7    6.2    5.8    5.6    5.4
Riverton              7.0    6.5    5.8    5.1    4.4    4.0    3.9
Petersburg            7.3    7.0    6.4    5.8    5.4    5.2    5.2
:Salt Creek
Greenview             2.4    2.3    2.0    1.7    1.5    1.3    1.2
:Sangamon River
Oakford             458.9  458.6  457.9  457.5  456.9  456.6  456.5
Chandlerville       446.3  445.9  445.2  444.8  444.2  443.9  443.8
:Embarras River
Lawrenceville        19.4   19.3   18.9   18.6   18.3   18.0   17.9
Ste. Marie            3.3    3.2    2.9    2.6    2.3    2.1    2.0
:Little Wabash River
Clay City             7.1    6.9    6.0    5.4    4.9    4.6    4.4
:Vermilion River
Danville              3.8    3.7    3.5    3.4    3.2    3.0    2.9

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

 

NWS Lincoln Hydrologic Service Area

 

USGS Monthly Streamflows
(December 2019)




 


Drought Monitor
(Issued December 3, 2019)



 

USGS Monthly Streamflows
(January 2020)


 

Drought Monitor
(Issued January 7, 2020)



 

USGS Monthly Streamflows
(February 2020)

 

Drought Monitor
(Issued February 4, 2020)

 

USGS Daily Streamflow
(March 11, 2020)



 

Drought Monitor
(Issued March 12, 2020)

 

Frost Depth Conditions
(March 12, 2020)


 

CPC Soil Moisture Percentile Map

 

Modeled Snow Depth
Mar 12, 2020
 
Modeled Snow Depth - Departure from Normal
Mar 12, 2020

 
Modeled Snow Water Equivalent (SWE)
Mar 12, 2020
 
NCRFC Ranked Simulated SWE
Mar 9, 2020
 
 
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 (MAR/APR/MAY)

 

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

 

Greater than 90% chance
of exceeding river flood levels (MAR/APR/MAY)

 

Advanced Hydrologic Prediction Service (AHPS)


Climate Prediction Center (CPC)