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Flood Potential Outlook
Issued by NWS Central Illinois
Issued by NWS Central Illinois
000
FGUS73 KILX 292015
ESFILX
ILC009-017-025-033-057-079-095-101-113-123-125-129-137-143-147-
155-159-167-169-179-183-203-092200-
PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE Lincoln IL
215 PM CST Thu Feb 29 2024
...2024 Spring Flood and Water Resources Outlook Number 2...
...Near normal to below normal likelihood for flooding across
central and southeast Illinois this spring...
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...
- Risk of flooding this spring is near normal to below normal across
central and southeast Illinois.
- Factors limiting flood potential this spring include: near normal
to below normal streamflows, no local or upstream snowpack, thawed
soils, deep layer soil moisture deficits.
- Springtime rains expected to be the primary driver for flooding.
WINTER WEATHER REVIEW...
--December--
Statewide Temperatures/Precipitation:
Information, courtesy of the Illinois State Climatologist, shows that
the preliminary statewide average December temperature was 39.2
degrees, 7.6 degrees above normal and the 3rd warmest on record going
back to 1895. For the second time in three years, Illinois
experienced an extremely mild December. All but three days were
warmer than normal in Decatur, and several days in the second and
fourth weeks of the month were 10 to 20 degrees warmer than normal.
This was the 2nd warmest December in Rockford, the 3rd warmest in
Peoria, and the 4th warmest in Chicago and Moline. None of the more
than 120 NWS observing stations in Illinois recorded a low
temperature in the
single digits. Many places hit the freezing mark only a handful of
nights.
December average temperatures ranged from the low 30s in northern
Illinois to the low 40s in southern Illinois, between 6 and 10
degrees above normal. The warmest place in the state was Du Quoin
with an average December temperature of 46.1 degrees. The coolest was
Stockton in Jo Daviess County with an average December temperature of
33.9 degrees. It is important to note that the nighttime low
temperatures in December were much higher than
normal. The preliminary average December minimum temperature is 32.2
degrees, which would be the 2nd highest on record statewide.
The mild December weather broke 20 daily high maximum temperature
records and 99 daily high minimum temperature records across
Illinois! No daily low maximum or daily low minimum temperature
records were broken.
The preliminary statewide average total December precipitation was
2.99 inches, 0.56 inches above normal and the 30th wettest on record
statewide.
The first month of climatological winter brought a more active storm
track to the Midwest than for most of the fall. December total
precipitation ranged from just over 4 inches in parts of northern
Illinois to less than 1 inch in parts of far southern Illinois. Most
of northern Illinois was around 1 inch wetter than normal, while most
of the state south of Interstate 64 was 1 to 3 inches drier than
normal in December.
As is often the case in milder Decembers, snowfall was hard to come
by across Illinois. Total snowfall ranged from around 4 inches in far
northwest Illinois to less than a tenth of an inch in southern
Illinois. This was between 1 and 8 inches below normal.
Local Temperatures/Precipitation/River Conditions:
Temperatures for December were above normal across the ILX Hydrologic
Service Area (HSA). They generally ranged from 7.5 degrees to 9
degrees above normal. Daily high temperatures ranged from the teens
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 mid 30s to the low 50s. They typically range from the teens to
the upper 20s.
Rainfall totals across most of the ILX HSA were above normal for the
month of December. However, far southeastern areas saw below normal
precipitation. Monthly precipitation ranged from 1.68 inches in
Hutsonville to 4.07 inches in Fisher. These totals ranged from 1.38
inches below normal to 1.62 inches above normal, respectively. This
equates to roughly 55 to 165 percent of normal precipitation for the
month.
The above normal precipitation in northern Illinois allowed for
drought improvement in those areas. In contrast, conditions worsened
across southern sections of the state, due to below normal
precipitation. While D0 (Abnormally Dry) and D1 (Moderate Drought)
conditions improved overall, areas of D2 (Severe Drought) expanded
from 6 percent to 19 percent month over month. This was most evident
across portions of west-central Illinois as well as the southern
third of the state.
With low streamflows and below normal soil moisture conditions, the
above normal December precipitation was not enough to cause flooding
issues across central and southeast Illinois.
U.S. Geological Survey (USGS) monthly average streamflow values for
December show overall near normal streamflows across mainly the
northern half of Illinois. Flows across the southern half of the
state were overall in the below normal to much below normal
categories.
--January--
Statewide Temperatures/Precipitation:
The Illinois State Climatologist notes that the preliminary statewide
average January temperature was 25.7 degrees, 1.0 degree above normal
and tied for the 57th coldest on record going back to 1895.
The very mild December weather spilled over into the new year as the
first 10 to 12 days of January had temperatures near to slightly
above normal. Extremely cold air moved into Illinois following a
series of winter storms and brought frigid weather across the state
for the middle part of the month. Daily temperature departures from
normal showed average temperatures were 10 to 30 degrees below
normal. Some of the coldest temperatures from that week included -25
degrees in Altona and -19 degrees in Moline. Strong northerly and
northwesterly winds added to the cold and pushed wind chills into the
-30 to -40 degree range. Water main breaks were reported across the
state, and several school districts closed for multiple days because
of the cold. Numerous deaths in the state were attributed to the cold
as well. Temperatures moderated in the final week of the month,
providing a well-deserved break from an Arctic winter.
January temperatures ranged from the low 20s in northern Illinois to
the mid 30s in southern Illinois. The southern half of the state was
1 to 3 degrees colder than normal. Despite the extreme cold mid-
month, northern Illinois was 1 to 2 degrees warmer than normal. The
coldest point in the state in January was Stockton in Jo Daviess
County at 20.1 degrees. The “warmest” point was Olmstead in Pulaski
County at 32.7 degrees.
The preliminary statewide average total January precipitation was
4.50 inches, 2.19 inches below normal and tied for the eighth wettest
on record statewide.
Precipitation was hard to come by for much of Illinois during the
last few months of 2023. Drought impacts are usually minimal in
winter, but there were many reports of unusually dry soils and low
streams and ponds at the start of the new year. While January did not
completely replenish all water lost last year, it took a big bite out
of the drought.
January total precipitation ranged from around 2.5 inches in
northwest Illinois to nearly 10 inches in far southern Illinois.
Everywhere in Illinois was wetter than normal in January, to the tune
of 1 to 4 inches, between 150% and 300% of normal monthly
precipitation. It was the eighth wettest January on record in
Champaign and Centralia, both with over 5 inches total.
Depending on where you are in Illinois, January is either the first
or second snowiest month of the year. If you live north or west of
the Illinois River, this was the case this past January. For the rest
of Illinois, January just brought more cold rain. Total January
snowfall ranged from less than half an inch in southern Illinois to
over 25 inches in northwest Illinois. The latter was 4 to 15 inches
above normal.
Most of the snow in January came immediately ahead of or during the
extreme cold in the middle of the month. Moline picked up more
snowfall between January 8 and January 18 than in all of 2023.
January was the second snowiest on record in Moline, only less than
2019. The 12th of January was also the second snowiest day on record
in Moline, with 15.4 inches. It was only less than on January 3,
1971.
The heavy snowfall in mid-January pushed the northwest corner of
Illinois 1 to 6 inches above normal on season-to-date snowfall.
Meanwhile, most of central and southern Illinois had 2 to 8 inches
below normal snowfall by that time.
Local Temperatures/Precipitation/River Conditions:
Temperature averages for January were overall near normal across the
ILX Hydrologic Service Area (HSA). Temperatures generally ranged from
1 degree below normal to 1 degree above. Daily high temperatures
ranged from the single digits below zero to the mid 50s. Normal highs
for January typically range into the low to mid 30s. Low temperatures
across the area ranged from low teens below zero to the mid 30s. They
typically range into the teens.
Liquid precipitation totals across the ILX HSA were well above normal
for the month of January. Monthly precipitation ranged from 2.87
inches in Mackinaw to 6.32 inches in Casey. These totals ranged from
0.70 to 3.07 inches above normal, respectively. This equates to
roughly 130 to 195 percent of normal precipitation for the month. The
above normal precipitation for January continued to erode drought
coverage across the state. Only areas of D0 (Abnormally Dry)
conditions remain across portions of southern and west-central
Illinois. Drought coverage dropped from to 54 to 17 percent
of the state.
With the above normal precipitation, we did see minor to moderate
river flooding. However, it was not widespread and began in the
latter half of the month. Flooding was seen along the Illinois River,
and portions of the Little Wabash and Sangamon rivers and largely
continued into February.
Bitterly cold temperatures mid-month caused appreciable ice
development on area rivers. This was followed by a rapid warm-up
along with widespread heavy rain. The frozen ground led to
significant runoff, which caused area rivers to swell and
mechanically break up the ice. The higher flows caused downstream
movement of the ice. As a result, there were a few instances of ice
jams along portions of the Mackinaw and Sangamon Rivers. Thankfully,
impacts from these ice jams were minor and short-lived.
USGS monthly streamflow for January shows overall near normal
streamflows across mainly the southern half of Illinois as well as
areas in the northwest. Flows across remainder of the state were
overall in the above normal to much above normal categories.
--February--
Local Temperatures/Precipitation/River Conditions:
The month of February, has seen daily average temperatures that are
well above normal. They generally ranged from around 8 to 12 degrees
above average across the ILX Hydrologic Service Area (HSA). In
contrast, precipitation for February has been well below normal...
generally ranging from 1 to 2 inches below average. Overall,
precipitation for the month ranged from 10 to 50 percent of normal.
The below normal precipitation for February has caused worsening
drought conditions across much of the Illinois. Some form of drought
is now reflected for 80 percent of the state, according to the latest
drought monitor.
With the overall drier conditions, river flooding that carried over
into February came to an end by the third week. Streamflows have
continued to decline and currently range in the normal to below
normal categories across central and southeast Illinois.
SOIL MOISTURE AND FROST DEPTH CONDITIONS...
Shallow soil moisture conditions across Illinois are near normal for
this time of year. However, deep layer soil conditions (down to 39
inches) continue to show an appreciable deficit across nearly the
entire state.
Drought conditions in Illinois have notably improved through the
winter season as a whole. The drought recovery is thanks to overall
above normal temperatures that minimized periods of frozen soils in
addition to
precipitation that fell in form of rain.
In late November, nearly 40 percent of Illinois was experiencing D0
(Abnormally Dry) conditions with about 40 percent in the D1 (Moderate
Drought) category...or worse. Only pockets of D0 conditions remained
by mid-February, covering portions of west-central and southern
Illinois and encompassing only about 20 percent of the state. Since
then, conditions have been overall dry. As a result, drought
conditions have expanded significantly across Illinois. The February
29th Drought Monitor issuance now shows nearly 75 percent of the
state within the D0 (Abnormally Dry) category with an additional 7
percent in the D1 (Moderate Drought) category.
With overall above normal temperatures this winter, frost was
afforded little opportunity to develop or persist across the area.
One exception was the Arctic outbreak we had in mid-January. That
stretch of frigid temperatures caused frost to develop down to 6 to
10 inches across our service area. However, the return to above
normal temperatures quickly thawed the soils across the area. As of
this issuance, Illinois remains free of frost.
Frost is not a concern going forward into the spring. The lack of
frost will allow for deeper infiltration of rainfall into the soil.
As a result, runoff potential will be reduced until soils moisten up
more thoroughly. If we get into a longer duration, wet weather
pattern then runoff potential and risk of flooding can increase with
time.
RIVER CONDITIONS...
As of this issuance, there is no river flooding that is currently
impacting Illinois. Information, courtesy of the U.S. Geological
Survey (USGS), shows
that streamflow conditions are overall near normal across most of
northern and central Illinois. In contrast, portions of central and
most of southern Illinois are in the below normal to much below
normal categories.
Thanks to the above normal temperatures the past few weeks, river ice
is not currently present on area rivers. With above normal
temperatures continuing as we head into the spring, ice jam flooding
will not be a concern.
WEATHER OUTLOOKS...
The weather pattern over the next 2 weeks will be somewhat active and
will bring a couple opportunities for precipitation across Illinois
over that time. As we look toward this weekend and into next week,
high temperatures will generally range into the 50s and 60s with lows
well above freezing. The next best chance for widespread
precipitation comes early to mid-next week. The warm temperatures
should allow this to fall mainly as rain across central and southeast
Illinois.
The 8 to 14 day outlook (Mar 7 to Mar 13) favors above normal
temperatures in Illinois with the highest likelihood across the
northern half of the state. Above normal precipitation is also
favored across Illinois over the same time period.
The most recent outlook for this spring (March / April / May) favors
above normal temperatures across Illinois with the highest likelihood
across far northeastern portions of the state. As for precipitation,
most of Illinois is favored for above normal precipitation this
spring with the highest likelihood across the southern third of the
state.
FLOOD OUTLOOK SUMMARY...
The risk of flooding this spring is near normal to below normal
across central and southeast Illinois. Any flooding that does occur
would most likely be in the minor category with isolated moderate
flooding possible.
Currently, there is no river flooding that is impacting Illinois as
streamflows are currently near normal to below normal. Soils are
thawed with shallow moisture conditions near normal. However, deeper
soils continue to show an appreciable deficit. As a whole, these
conditions are not contributory toward enhanced flood potential this
spring.
Spring rains will be the primary driver of flooding this year since
other hydrometeorological conditions are not significant contributing
factors. Again, expectations are for isolated minor to moderate
flooding this spring. However, if we get into a very wet springtime
pattern then more widespread flooding is possible, but would most
likely be minor in severity.
--------------------------------------------------------------------
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: 03/04/2024 - 06/02/2024
: 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 56 42 52 <5 <5
Peoria 18.0 22.0 28.0 : 64 66 28 36 <5 <5
Peoria L/D 447.0 449.0 455.0 : 52 59 31 38 <5 <5
Havana 14.0 17.0 23.0 : 82 84 63 62 9 22
Beardstown 14.0 18.0 28.0 : 76 79 52 60 <5 7
:Mackinaw River
Congerville 13.0 14.0 20.0 : 19 21 14 16 <5 <5
:Spoon River
London Mills 15.0 21.0 24.0 : 43 47 6 5 <5 <5
Seville 22.0 25.0 30.0 : 35 40 19 17 <5 <5
:Sangamon River
Monticello 13.0 17.0 20.0 : 61 70 5 6 <5 <5
Riverton 23.0 26.0 29.0 : 14 12 <5 <5 <5 <5
Petersburg 23.0 24.0 33.0 : 21 24 17 15 <5 <5
:Salt Creek
Greenview 16.0 17.0 20.0 : 15 17 11 11 <5 <5
:Sangamon River
Oakford 471.0 472.9 478.5 : 26 38 17 19 <5 <5
Chandlerville 456.6 459.0 462.0 : 42 49 19 23 <5 <5
:Embarras River
Lawrenceville 30.0 37.0 41.0 : 70 75 23 19 <5 <5
Ste. Marie 19.0 20.0 27.0 : 35 35 24 23 <5 <5
:Little Wabash River
Clay City 18.0 22.0 25.0 : 85 85 18 21 <5 <5
:Vermilion River
Danville 18.0 22.0 28.0 : 15 23 5 12 <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: 03/04/2024 - 06/02/2024
Location 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:Illinois River
Henry 16.4 16.7 20.3 23.3 25.8 27.3 28.9
Peoria 13.0 13.2 16.1 19.7 22.3 23.6 25.5
Peoria L/D 436.1 436.5 443.6 447.1 449.8 450.9 452.9
Havana 11.0 12.5 15.0 18.1 21.3 22.8 25.5
Beardstown 11.2 12.0 14.3 18.2 22.9 25.4 27.3
:Mackinaw River
Congerville 3.8 4.3 6.2 9.3 11.7 14.9 16.3
:Spoon River
London Mills 5.4 6.3 9.8 13.1 18.4 20.3 22.1
Seville 9.7 10.4 14.7 17.5 24.4 26.6 27.9
:Sangamon River
Monticello 9.0 9.9 12.1 13.5 14.8 16.1 17.0
Riverton 9.3 12.3 16.2 18.5 21.1 23.2 25.9
Petersburg 8.1 10.4 13.7 16.6 21.0 24.9 27.3
:Salt Creek
Greenview 4.3 4.9 7.7 10.5 12.5 17.4 20.0
:Sangamon River
Oakford 460.1 461.9 464.7 468.2 471.6 473.9 475.5
Chandlerville 447.5 449.5 452.3 455.7 458.5 460.5 461.8
:Embarras River
Lawrenceville 24.6 26.3 29.4 32.6 36.7 38.8 39.5
Ste. Marie 6.6 9.2 12.5 17.7 19.9 21.4 22.9
:Little Wabash River
Clay City 16.4 17.3 19.6 20.8 21.6 22.4 23.7
:Vermilion River
Danville 6.9 8.2 10.1 12.1 15.3 19.4 22.3
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: 03/04/2024 - 06/02/2024
Location 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:Illinois River
Henry 15.3 15.2 15.0 14.9 14.7 14.5 14.3
Peoria 12.4 12.3 12.1 12.0 11.6 10.6 10.6
Peoria L/D 434.2 433.9 432.9 432.1 431.2 430.6 429.9
Havana 7.4 7.1 6.3 5.6 5.0 4.9 4.8
Beardstown 10.7 10.3 10.2 9.9 9.7 9.3 9.1
:Mackinaw River
Congerville 1.9 1.7 1.5 1.4 1.2 1.0 1.0
:Spoon River
London Mills 3.7 3.3 3.0 2.8 2.4 2.0 1.8
Seville 7.0 6.6 6.4 6.0 5.6 5.2 5.0
:Sangamon River
Monticello 7.0 6.8 6.4 6.1 5.7 5.2 4.9
Riverton 6.5 6.1 5.7 5.1 4.4 4.0 3.8
Petersburg 6.8 6.7 6.2 5.8 5.4 5.3 5.2
:Salt Creek
Greenview 2.2 2.0 1.9 1.6 1.4 1.1 1.0
:Sangamon River
Oakford 458.4 458.1 457.7 457.4 456.9 456.5 456.4
Chandlerville 445.8 445.5 445.1 444.8 444.3 443.9 443.8
:Embarras River
Lawrenceville 18.7 18.4 17.8 17.7 17.6 17.4 17.1
Ste. Marie 2.7 2.6 2.2 2.1 2.0 1.7 1.4
:Little Wabash River
Clay City 6.6 5.8 4.8 4.7 4.6 4.4 4.2
:Vermilion River
Danville 3.7 3.6 3.5 3.3 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.
The third and final issuance of the Spring Flood Outlook for central
and
southeast Illinois will be on Thursday, March 14th. The NOAA
National Spring Flood Outlook will be issued on Thursday, March 21st.
$$
DRH
- National Weather Service
- Northern Indiana Weather Forecast Office
- 7506 E 850 N
- Syracuse, IN 46567
- 574-834-1104
- Page Author: IWX Webmaster
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- Page last modified: Sep 19th, 2023 19:10 UTC