2014 Spring Flood Outlook #2

 

PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE LINCOLN IL
105 PM CST THU MAR 06 2014
 
...2014 Spring Flood and Water Resources Outlook Number 2...
 
...Above normal potential for flooding along the Illinois River with
near normal probabilities elsewhere across central and southeast
Illinois...
 
This flood outlook covers the Lincoln Hydrologic Service Area (HSA)
which encompasses 35 counties in central and southeast Illinois. It
includes the following rivers...
 
- Illinois River from Henry to Beardstown
- Spoon River from London Mills to Seville
- Mackinaw River at Congerville
- Sangamon River from Monticello to Chandlerville
- Salt Creek at Greenview
- Little Wabash River near Clay City
- Embarras River from Ste. Marie to Lawrenceville
 
These flood outlooks are issued in late winter and early spring, in
addition to the 7 day river forecasts that are issued when river
forecast locations are in flood or are forecast to rise above flood
stage. They are based on current streamflows, soil conditions, snow
pack, as well as short/long range weather forecasts.
 
Flood Outlook Highlights...
 
There have been no major changes to spring flood potential since the
first outlook was issued on February 20th. The risk of flooding from
the late winter into early spring is overall near normal across most
of central and southeast Illinois. However, the likelihood for minor
to moderate flooding along the Illinois River is projected to be
above normal this spring.
 
Those locations with near normal probabilities for flooding, or those
that usually flood in the spring will likely see typical conditions
this season. Those locations with above normal probabilities will see
a greater chance of flooding when compared to a normal year.
 
Ice jams and associated flooding remain a concern as we head further
into March. Many area rivers still have considerable ice coverage.
Ice jams can cause rapid rises in water levels in the area of the
jam. Those living near rivers and streams should remain aware of
river conditions in their area.
 
 
Winter Weather Review...
 
--December--
 
Information courtesy of the Illinois State Climatologist shows that
the average statewide precipitation for December was 2.50 inches,
which is slightly below normal. However, precipitation varied widely
across Illinois. Conditions were very dry across northern and central
Illinois, while much wetter conditions were observed in southern
sections of the state.
 
Across the ILX HSA, precipitation totals for December were overall
below normal. However, a few areas in our southeast observed above
normal precipitation. Monthly precipitation totals ranged from 1.13
inches in Galesburg to 4.97 inches in Palestine. These totals ranged
from 1.14 inches below normal to 1.68 inches above normal,
respectively. This equates to precipitation that ranged from around
50 to 150 percent of normal.
 
Temperatures for December averaged below normal across the ILX HSA,
ranging from 2 to 4 degrees below normal. High temperatures had large
swings, ranging from the teens to the upper 60s. Normal highs for
this month range from the low 30s to the low 40s. Low temperatures
ranged from the single digits below zero to the mid 40s in December.
They normally range from the teens to the upper 20s.
 
--January--
 
The State Climatologist notes that snowfall for January was above
average across most of Illinois with the exception of southern
sections. Snowfall amounts ranged from as little as 1 to 6 inches in
far southern Illinois to 25 to 30 inches in northeast portions of the
state. The remainder of Illinois, on average, saw 10 to 20 inches.
 
The combination of water content of the snow and a few rain events
resulted in a state-wide precipitation total of 1.76 inches. This is
just slightly below the normal of 2.12 inches. However, some areas of
the state were below average in January, especially south of
Interstate 70 where winter-time precipitation is typically heavier
than was experienced this year.
 
Across the ILX HSA, precipitation totals for January were near normal
across northern portions of the area while southern locations trended
below normal. Monthly precipitation totals ranged from 1.21 inches in
Rushville to 2.93 inches in Danville. These totals ranged from 0.68
inches above normal to 0.42 inches below normal, respectively. This
equates to precipitation that ranged from around 75 to 130 percent of
normal.
 
Temperatures for January averaged well below normal. Monthly averages
reached up to 7 degrees below normal. High temperatures across the
area ranged from the single digits below zero to the mid 50s. Normal
highs for this month range from the low to mid 30s. Low temperatures
across the area ranged from the teens below zero to the low 30s. They
typically range in the teens.
 
--February--
 
Heading into February, we continued the colder than normal trend.
However, the third week of the month saw the first above freezing
temperatures in weeks. In fact temperatures pushed into the 40s, 50s,
and 60s across Illinois.
 
Ahead of that warm-up, the snowpack across central and southeast
Illinois ranged from 12 to 17 inches in our northernmost counties
with 6 to 10 inches across most other areas. Our southernmost tier of
counties had snow depths from 1 to 4 inches. The liquid content of
the snow generally ranged from 1 to 2 inches across much of the HSA.
 
After that event, there was little to no snow across the southern
half of Illinois. Snow depths in the northernmost counties of our HSA
generally ranged from 1 to 4 inches. The liquid water content of that
snow ranged from a trace to a half an inch. The remainder of February
was generally quiet with a return to below normal temperatures across
Illinois.
 
--Winter Season Stats--
 
Temperatures...
 
This winter season as a whole has brought us record cold temperatures
in many areas. Most other locations that did not break their records
were still among the top 5 coldest on record. The table below shows
how the daily mean temperatures rank historically as of March 5th...
 
 
                2013-14                 Coldest               Records
Location        Rank        Temp        Winter                 Began
---------------------------------------------------------------------
Danville        7th         23.5        1976-77 (20.6)         1895
Decatur         6th         22.6        1977-78 (20.9)         1893
Effingham       6th         24.1        1977-78 (20.5)         1892
Galesburg       2nd         16.5        1978-79 (15.4)         1895
Hoopeston       7th         21.3        1977-78 (18.9)         1887
Jacksonville    7th         22.6        1977-78 (19.1)         1895
Lincoln        -1st-        20.6        1977-78 (20.9) old     1905
Normal          2nd         19.1        1935-36 (19.0)         1893
Olney           4th         25.1        1917-18 (22.0)         1890
Paris           4th         21.6        1977-78 (20.6)         1893
Peoria          8th         20.2        1978-79 (17.0)         1883
Rushville       2nd         19.7        1935-36 (19.5)         1890
Springfield     8th         22.8        1977-78 (19.8)         1879
Tuscola         4th         21.5        1977-78 (20.4)         1893
Urbana          9th         21.5        1977-78 (20.2)         1888
 
Snowfall...
 
The snowfall totals observed this winter are well above normal across
the board. Most locations are in the top 10 snowiest on record. This
is in stark contrast to last winter season when snowfall over central
and southeast Illinois was well below normal.
 
The table below shows observed snowfall in inches through March 5th
for several cities and compares how they rank historically for the
entire winter season.
 
            2013-14                             Snowiest      Records
Location    Winter   Rank  Normal  Departure     Winter        Began
---------------------------------------------------------------------
Charleston   33.3    10th   15.6    +17.7     45.1 (1995-96)   1896
Danville     45.1     2nd   15.9    +29.2     45.4 (1942-43)   1895
Decatur      37.6     5th   14.6    +23.0     49.7 (1981-82)   1893
Effingham    35.4     7th   11.9    +23.5     40.6 (1977-78)   1892
Galesburg    46.1     3rd   20.9    +25.2     52.8 (1978-79)   1895
Hoopeston    53.9     2nd   16.1    +37.8     77.2 (1903-04)   1887
Jacksonville 31.7    16th   15.3    +16.4     54.0 (1977-78)   1895
Lincoln      44.0     2nd   18.9    +25.1     45.0 (1981-82)   1905
Mattoon      39.9     5th   13.2    +26.7     49.7 (1977-78)   1893
Normal       48.7     2nd   18.1    +30.6     57.8 (1959-60)   1893
Olney        28.0     9th   10.8    +17.2      3.3 (1895-96)   1890
Paris        37.4     7th   21.5    +15.9     71.5 (1977-78)   1893
Peoria       53.4    -1st-  21.8    +31.6      2.5 (2010-11)   1883
Rushville    38.5     7th   14.3    +24.2     61.3 (1964-65)   1890
Springfield  43.2     3rd   18.6    +24.6     52.1 (1977-78)   1879
Tuscola      43.5     4th   16.4    +27.1     49.7 (1977-78)   1893
Urbana       41.1     7th   20.8    +20.3      7.2 (1977-78)   1888
 
 
Soil Moisture and Frost Depth Conditions...
 
Soil moisture conditions across the northern two thirds of Illinois
ranged from the 5th to 30th percentile. There were also a few areas,
especially in central Illinois that ranked even lower. Locations
across the southern third of the state were in the 30th to 70th
percentile, which is in the normal range.
 
Drought conditions have improved slowly over the winter season. The
latest drought monitor from March 4th shows D1 (Moderate Drought)
across approximately one quarter of the ILX Hydrologic Service Area
(HSA). The D1 conditions extend from southern Scott and Morgan
counties northeastward into southern McLean and Western Champaign
counties. An area of D0 (Abnormally Dry) conditions encompasses the
D1 outlined areas, surrounding them by one tier of counties.
 
The long cold spells this winter have caused frost depths across
central Illinois to push down to 10 to 16 inches as of this outlook.
Southeastern Illinois locations are currently reporting frost depths
of 5 to 7 inches.
 
River Conditions...
 
Even though we did experience a significant warm-up the third week of
February, temperatures came back down to below normal levels very
quickly. However, the combination of warm temperatures, frozen ground
and rapid snowmelt along with rainfall caused a significant amount of
runoff into the river system. This was significant enough to cause
mainly minor flooding along many rivers and streams across central
and southeast Illinois. The increased streamflows also caused river
ice to breakup and begin flowing. There were multiple reports of ice
jams, some of which cause localized flooding.
 
Currently all the rivers, with the exception of a few locations along
the Illinois River have fallen below flood stage. Most river gaging
locations are currently within the normal range for streamflows for
this time of year.
 
Unfortunately, many rivers still have an appreciable amount of ice on
them which could lead to ice jam problems in the near future. We are
looking at a significant warm-up over the next week. High
temperatures will be warming into the 40s and 50s with overnight lows
near or below freezing. This will aid in a more tempered melt process
in the short term. However, if we do get a big rain event while the
ground is still frozen, then we will have an increased flood risk,
including flooding caused by ice jams.
 
If ice jams do form, they have the potential to produce rapid
flooding in the vicinity of the jam. Those living along rivers and
streams should be on the lookout for signs of ice jam formation as we
head into this warm-up period and beyond.
 
Weather Outlooks...
 
The weather pattern across the Midwest will be fairly quiet over the
next week. There will be a couple of weak weather systems moving
through, but they are not expected to produce much in the way of
precipitation. The forecast over this time period calls for
temperatures to rise to near normal levels.
 
The 8 to 14 day outlook (Mar 13th to Mar 19th) indicates a greater
than 50 percent likelihood for below normal temperatures across
Illinois, with a greater than 60 percent likelihood across the
eastern half. There is also greater than 33 percent likelihood for
below normal precipitation across the state during this time period.
 
The 90 day outlook (March, April, and May) for Illinois shows greater
than 33 percent likelihood for below normal temperatures across the
northern third of Illinois. There are no strong signals for
temperatures trends across the rest of the state. There is greater
than 33 percent likelihood for above normal precipitation across the
southern half of Illinois with no strong precipitation trends noted
across the remainder of the state.
 
Flood Outlook Summary...
 
Above normal probabilities for flooding are forecast for the Illinois
River with overall near normal probabilities elsewhere across central
and southeast Illinois. The likelihood for minor flooding is highest
along the Illinois River as well as the Embarras and Little Wabash
Rivers this spring.
 
A warm-up in temperatures over the next week will melt the remaining
snow across central and southeast Illinois. It will also help to melt
river ice that remains along many rivers. Ice jams still remain a
risk for those people living along rivers and streams. Please remain
aware of river conditions in your area. If you come across a flooded
area remember, Turn Around Don`t Drown.
 
With the ground still frozen, any significant rain/snow producing
weather systems in the near term will create an enhanced flood risk.
The severity of these flood events would be determined by the amount
precipitation/snowmelt and current hydrologic conditions.
 
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: 3/10/2014 - 6/8/2014
 
                                       :    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 : 83   56   64   44   <5   <5
Peoria              18.0   22.0   28.0 : 89   63   50   27   <5   <5
Havana              14.0   17.0   23.0 : 90   69   61   41   <5   <5
Beardstown          14.0   18.0   28.0 : 92   78   70   53   <5   <5
:Mackinaw River
Congerville         13.0   14.0   20.0 : 26   21   16   13   <5   <5
:Spoon River
London Mills        15.0   21.0   24.0 : 56   50   35   27   10    7
Seville             22.0   25.0   30.0 : 44   43   29   21   <5   <5
:Sangamon River
Monticello          13.0   17.0   20.0 : 64   64    6    7   <5   <5
Riverton            23.0   26.0   29.0 : 10   10    6   <5   <5   <5
Petersburg          23.0   24.0   33.0 : 15   15   12   13   <5   <5
:Salt Creek
Greenview           16.0   17.0   20.0 : 13   15   13   13    7    7
:Sangamon River
Oakford            471.0 472.9 478.5 : 24   30   15   16   <5   <5
Chandlerville      456.6 459.0 462.0 : 38   44   16   18   <5   <5
:Little Wabash River
Clay City           18.0   22.0   25.0 : 91   89   19   17   <5   <5
:Vermilion River
Danville            18.0   22.0   28.0 : 24   19   12    8   <5   <5
:Embarras River
Lawrenceville       30.0   37.0   41.0 : 71   68   18   16   <5   <5
Ste Marie           19.0   20.0   27.0 : 30   29   23   21   <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: 3/10/2014 - 6/8/2014
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Illinois River
Henry               20.5   21.7   23.5   25.5   26.5   28.2   28.8
Peoria               16.2   18.1   19.7   22.1   23.1   24.7   25.4
Havana               13.7   14.7   16.0   18.1   19.5   20.8   22.5
Beardstown           13.5   15.5   17.4   21.8   24.3   26.0   27.5
:Mackinaw River
Congerville           6.2    6.5    7.7   10.7   13.1   16.3   16.9
:Spoon River
London Mills          9.9   10.3   12.8   16.4   22.2   24.1   26.3
Seville              13.4   14.4   17.1   21.0   25.4   27.3   30.7
:Sangamon River
Monticello           10.8   11.0   12.4   13.7   15.3   16.4   18.1
Riverton             11.2   13.1   15.8   18.2   21.3   23.4   26.6
Petersburg            9.5   10.9   12.7   15.4   19.4   25.0   28.1
:Salt Creek
Greenview             5.8    6.9    9.2   11.4   14.0   18.2   21.6
:Sangamon River
Oakford             461.7 462.8 464.9 468.0 471.2 473.8 475.5
Chandlerville       449.1 450.3 452.5 455.5 458.1 460.4 461.8
:Little Wabash River
Clay City            14.4   17.0   19.3   20.6   21.4   23.0   23.5
:Vermilion River
Danville              8.1    8.6   11.4   14.5   17.8   22.8   24.4
:Embarras River
Lawrenceville        26.1   26.8   29.5   33.1   35.7   38.9   39.9
Ste Marie             8.8    9.4   12.5   16.4   19.7   23.3   24.0
 
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: 3/10/2014 - 6/8/2014
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Illinois River
Henry                15.2   15.1   15.1   14.9   14.7   14.5   14.4
Peoria               12.4   12.3   12.2   12.0   11.0   10.6   10.6
Havana                8.1    7.8    6.8    6.0    5.0    4.9    4.9
Beardstown           10.8   10.7   10.4   10.0    9.7    9.4    9.1
:Mackinaw River
Congerville           2.1    1.9    1.6    1.4    1.2    1.1    1.1
:Spoon River
London Mills          4.2    3.9    3.5    3.3    2.9    2.7    2.6
Seville               7.7    7.2    6.7    6.4    5.9    5.6    5.5
:Sangamon River
Monticello            7.5    7.1    6.6    6.3    5.9    5.5    5.3
Riverton              6.9    6.1    5.3    4.6    4.1    3.8    3.6
Petersburg            7.5    7.0    6.5    6.0    5.6    5.4    5.3
:Salt Creek
Greenview             2.8    2.4    2.0    1.7    1.4    1.2    1.1
:Sangamon River
Oakford             459.1 458.6 457.8 457.4 456.9 456.6 456.5
Chandlerville       446.4 445.9 445.1 444.7 444.1 443.9 443.8
 
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 http://www/weather.gov/ilx for more official
NWS river and weather information. To view graphical AHPS
information, including forecasts, select Rivers and Lakes from the
list on the left side menu. Full AHPS graphics are available for all
forecast points in the ILX HSA.
 
For 30 to 90 day temperature and precipitation outlooks, visit the
web page of the Climate Prediction Center at http://www.cpc.noaa.gov.
 
This will be the last issuance of the Spring FloodOutlook for
central and southeast Illinois unless conditions warrant an update.
The NOAA National Spring FloodOutlook will be issued on Thursday,
March 20th. National Flood Awareness Week is March 17th to the 21st.
 
$$
 
DRH
 


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