Flood Potential Outlook
Issued by NWS North Platte, NE

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FGUS73 KLBF 200544 CCA
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NEC017-031-063-069-085-089-101-103-111-040000-

PROBABILISTIC HYDROLOGIC OUTLOOK...CORRECTED
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1141 PM CST THU FEB 19 2015

...Spring Flood And Water Resource Outlook...

This Spring Flood and Water Resource Outlook is for the North Platte
Hydrologic Service Area, which covers western and north central
Nebraska. The river basins include: the North Platte and South
Platte Rivers and the Platte River in the eastern panhandle and
western Nebraska, Frenchman Creek and Stinking Water Creek in
southwest Nebraska, the Loup and Dismal Rivers in the Sandhills of
Nebraska, and portions of the Elkhorn and Niobrara Rivers in north
central Nebraska.

...Low Flood Potential For Significant Flooding...

.Flood Outlook Summary...

At this time, the potential for significant flooding from snowmelt
is low. Any further significant snowfall later this season could
modify the potential for flooding due to snowmelt.

The flood potential for ice jam related flooding is near average on
area rivers and streams. Rivers across the area are currently ice
free, however cold temperatures are forecast over the next several
weeks which could again enhance ice jam flooding concerns.

The flood potential for flooding from reservoir releases is near
average. The potential will vary based on the amount of water
released due to downstream demands this spring.

The potential for rainfall induced flash flooding is not
quantifiable. This type of flooding is most likely to occur during
the spring and summer months.

.Snow Cover And Liquid Water Content...

As of February 19th, a strip of up to 2 inches of snow is on the
ground from northern Cherry County and Western Keya Paha County down
through northeast Custer County to southwest Wheeler County. Liquid
equivalent content of this snow cover is less than two tenths of an
inch.

All other locations are free of snow cover at this time.

.Seasonal Precipitation...

Precipitation so far this water year, since October 1, 2014 has been
slightly below average. After October and November, which were dry
months, above average precipitation fell in December to help
alleviate the dry conditions. January was another dry month, but
since it is one of the driest months of the year, the drier than
normal conditions did not contribute to the overall dryness of the
area.

As of mid-February, most locations have seen above average
precipitation, with the exception of far southwest Nebraska, which
is currently near two-tenths of an inch below average for the month.

.Soil Conditions And Frost Depths...

Soil moisture varies across western and north central Nebraska. Much
below normal ground water depths are being observed across southwest
Nebraska, while both surface and root zone soil moisture is below
average over much of southern Nebraska. The northern half of
Nebraska is observing near to above average soil moisture, with
locations over the northern panhandle observing well above normal
soil moisture.

Warm weather in late January and early February allowed much of the
frost to thaw across the region. However, the return of colder
temperatures has caused frost to develop again, with 6 inches being
observed over southwest Nebraska. With the colder air in the
forecast, frost depths will likely deepen over the next week.

.River Conditions...

Recent warm conditions have allowed the majority of rivers across the
area to flow ice free. In locations where ice does remain on the
rivers, flows are not being impacted at a high degree. Streamflow
observations across the Republican River Basin are indicating well
below normal flows, ranging from 6 to 25 percent of average across
the basin. Streamflows across the remainder of western and north
central Nebraska are near to above average for this time of year.

.Reservoir And Snowpack Conditions...

Normal operations are ongoing at reservoirs along the North Platte
River for this time of year. Releases from these dams have been very
limited through the winter months, with inflows generally coming
from melting snow. Because of these operations, reservoir levels
have risen through the winter months. The reservoirs across Wyoming,
as well as Lake McConaughy, are reporting levels at 75
percent or less of capacity as of mid February.

Snowpack across the North Platte River Basin is indicating below
average spring snowmelt runoff as of mid February. Snow water
equivalent across the basin is registering at 70 to 90 percent of
average. The South Platte River Basin is indicating snow water
equivalent slightly higher, but remaining below average at 90 to 100
percent of average.

.Drought...

According to the U.S. Drought Monitor, abnormally dry conditions
were present across southern Nebraska, roughly south of a line from
Imperial through Stapleton to Burwell. The remainder of western and
north central Nebraska is currently void of drought conditions.
With February being climatologically one of the driest months of the
year, even if the remainder of the month experiences dry conditions,
drought conditions are not expected to expand across western and
north central Nebraska.

.Weather Outlooks...

According to the Climate Prediction Center, the latest 8 to 14 day
outlook valid for the end of February through the first week of March
calls for higher chances for below average temperatures for all of
western and north central Nebraska. The precipitation outlook calls
for equal chances for below average, average, or above average
precipitation for all of western and north central Nebraska.

The latest 30 day outlook for March calls for equal chances for
below average, average, or above average temperatures and
precipitation.

The latest 90 day outlook for March, April, and May calls for equal
chances for below average, average, or above average temperatures
across all of Nebraska. The precipitation outlook calls for equal
chances for below average, average, or above average precipitation
for much of Nebraska, with the exception of southwest Nebraska which
has higher chances for above average precipitation.

.Numerical River Outlooks...

For the North and South Platte Rivers...long range probabilistic
outlooks are issued for the water year from January through June.
All other months and locations are 90 day probabilistic outlooks.

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:  2/21/2015 - 9/30/2015

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:North Platte River
Lisco                4.0    5.0    6.0 :   9   20    6   13   <5    9
Lewellen             7.5    8.5    9.5 :  11   27   <5   17   <5   11
North Platte         6.0    6.5    7.0 :  96   26    8   16    5   13
:South Platte River
Roscoe               9.0   11.0   13.0 :  31   15   14    8    5   <5
North Platte        13.0   14.0   15.0 :   9    7    6   <5   <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: 2/21/2015 - 9/30/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:North Platte River
Lisco                 2.2    2.2    2.2    2.3    2.7    3.7    5.2
Lewellen              6.6    6.6    6.6    6.7    7.1    7.7    8.3
North Platte          6.0    6.1    6.2    6.2    6.3    6.5    7.0
:South Platte River
Roscoe                6.0    6.1    6.9    8.1    9.5   11.8   13.1
North Platte          7.5    7.7    8.7    9.9   10.8   12.9   14.5

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: 2/21/2015 - 9/30/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:North Platte River
Lisco                 1.0    1.0    0.8    0.7    0.7    0.6    0.6
Lewellen              5.4    5.3    5.3    5.2    5.1    5.1    5.0
North Platte          4.6    4.5    4.4    4.4    4.4    4.3    4.3
:South Platte River
Roscoe                3.3    2.9    2.8    2.8    2.7    2.7    2.7
North Platte          6.1    6.1    6.0    6.0    5.8    5.8    5.6


The following are the 90 day probabilistic outlooks.

...Table 1--Probabilities for minor, moderate and major flooding...
                    Valid Period:  2/21/2015 - 5/22/2015

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Elkhorn River
Ewing 1N             9.0   10.0   12.0 :  <5   <5   <5   <5   <5   <5
:Platte River
Brady North Chann    7.5    9.0   11.0 :  16   18   11   10    5   <5
:Frenchman Creek
Palisade             7.0    8.0    9.0 :  <5   <5   <5   <5   <5   <5
:Stinking Water Creek
Palisade 2NW        10.0   11.0   12.0 :  <5   <5   <5   <5   <5   <5
:Niobrara River
Sparks               6.0   10.0   12.0 :  <5   <5   <5   <5   <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: 2/21/2015 - 5/22/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Elkhorn River
Ewing 1N              3.6    3.7    3.8    4.1    4.5    5.2    6.0
:Platte River
Brady North Chann     2.6    2.6    3.0    4.4    6.5    9.5   10.6
:Frenchman Creek
Palisade              2.7    2.7    2.7    2.9    3.9    5.7    6.3
:Stinking Water Creek
Palisade 2NW          2.9    2.9    3.1    3.6    4.5    6.6    7.6
:Niobrara River
Sparks                3.1    3.1    3.3    3.4    3.5    3.6    3.7

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: 2/21/2015 - 5/22/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Elkhorn River
Ewing 1N              3.2    3.2    3.2    3.1    3.1    3.1    3.1
:Platte River
Brady North Chann     1.8    1.7    1.7    1.6    1.5    1.3    1.2
:Frenchman Creek
Palisade              2.6    2.6    2.5    2.5    2.5    2.4    2.3
:Stinking Water Creek
Palisade 2NW          2.8    2.7    2.7    2.5    2.3    2.3    2.3
:Niobrara River
Sparks                2.7    2.7    2.7    2.6    2.6    2.5    2.5

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.

Visit our web site weather.gov/lbf for more weather and water
information.

This is the first spring flood and water resource outlook for 2015.
Regular long-range probabilistic outlooks are typically issued near
the end of the month throughout the year. The next scheduled spring
flood and water resource outlook for these locations will be issued
on March 5, 2015.

$$

Brooks






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