Flood Potential Outlook
Issued by NWS North Platte, NE

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FGUS73 KLBF 052149
ESFLBF
NEC017-031-063-069-085-089-101-103-111-

PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE NORTH PLATTE NE
349 PM CST THU MAR 5 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. Although the winter season is coming to an end, major snow
storms can still occur with further significant snowfall modifying
the potential for flooding due to snowmelt.

The potential for ice jam related flooding is near or below
average on area rivers and streams. Most rivers across the area are
currently ice free, however cold air in place during late February
and early March has kept some rivers ice covered. The outlook for
the next week is for near or above average temperatures which will
lower the chances for freeze-up ice jams although break-up ice jams
will be possible where ice currently exists.

The 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 later spring and summer months.

.Snow Cover And Liquid Water Content...

As of March 5th, no deep snowpack existed across western and
north central Nebraska. There were a few areas with minimal snow
cover, up to 2 inches. Liquid water equivalent of this snow cover
is less than two tenths of an inch. With near or above average
temperatures forecast over the next week any snow cover will likely
diminish.

.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
average conditions did not contribute to the overall dryness of the
area. February saw slightly below average precipitation, which
helped keep the area from dropping too far below average for the
season.

.Soil Conditions And Frost Depths...

Soil moisture varies across western and north central Nebraska. Much
below average 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 average
soil moisture.

Cold temperatures the last week of February through early March have
caused an increase in frost depth across western and north central
Nebraska with depths up to a foot. The return of warmer temperatures
should allow some thaw to occur through the next week.

.River Conditions...

Some rivers do remain ice covered as of March 5th, however most are
ice free. Restrictions to flows where ice cover does exist have been
minimal. Observations across the Republican River Basin are
indicating well below average flows, ranging from 6 to 25 percent of
average across the basin. Rivers across the remainder of western and
north central Nebraska are experiencing near to above average
streamflows 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 near 75 percent of
capacity or less early March.

Snowpack across the North Platte River Basin is indicating below
average for spring snowmelt runoff as of early March. Snow water
equivalent across the basin is registering at 80 to 95 percent of
average. The South Platte River Basin is indicating snow water
equivalent slightly above average, at around 110 percent.

.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.

.Weather Outlooks...

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

The latest 90 day outlook for March, April, and May calls for equal
chances for below average, average, or above average temperatures
and precipitation across all of Nebraska.

.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:  3/7/2015 - 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 :   8   20   <5   13   <5    9
Lewellen             7.5    8.5    9.5 :  13   27   <5   17   <5   11
North Platte         6.0    6.5    7.0 :  96   26    7   16    5   13
:South Platte River
Roscoe               9.0   11.0   13.0 :  31   15   15    8    7   <5
North Platte        13.0   14.0   15.0 :  10    7    8   <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: 3/7/2015 - 9/30/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:North Platte River
Lisco                 2.4    2.4    2.5    2.6    2.8    3.5    4.5
Lewellen              6.7    6.7    6.7    6.9    7.1    7.5    8.0
North Platte          6.0    6.1    6.2    6.2    6.3    6.4    7.0
:South Platte River
Roscoe                6.1    6.4    6.8    8.2    9.4   11.9   13.3
North Platte          7.8    8.1    8.6    9.9   10.9   13.1   14.6

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: 3/7/2015 - 9/30/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:North Platte River
Lisco                 1.1    1.1    1.0    0.9    0.9    0.9    0.8
Lewellen              5.4    5.4    5.2    5.2    5.1    5.1    5.0
North Platte          4.5    4.5    4.4    4.4    4.4    4.3    4.3
:South Platte River
Roscoe                3.0    2.3    2.1    2.0    2.0    2.0    2.0
North Platte          6.1    6.1    6.1    6.1    6.1    6.1    6.1


The following are the 90 day probabilistic outlooks.

...Table 1--Probabilities for minor, moderate and major flooding...
                    Valid Period:  3/7/2015 - 6/5/2015

                                       :    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 :  18   22   10   10    8   <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: 3/7/2015 - 6/5/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Elkhorn River
Ewing 1N              3.8    3.8    3.9    4.1    4.4    5.2    6.3
:Platte River
Brady North Chann     3.9    4.1    4.6    5.7    6.7    9.1   11.8
:Frenchman Creek
Palisade              2.7    2.7    2.7    3.2    4.2    5.7    6.7
:Stinking Water Creek
Palisade 2NW          3.0    3.2    3.3    3.7    4.9    6.3    7.3
:Niobrara River
Sparks                2.9    2.9    3.0    3.1    3.3    3.6    4.7

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: 3/7/2015 - 6/5/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Elkhorn River
Ewing 1N              3.2    3.2    3.1    3.1    3.1    3.0    3.0
:Platte River
Brady North Chann     2.0    2.0    1.9    1.9    1.9    1.8    1.8
:Frenchman Creek
Palisade              2.6    2.6    2.6    2.5    2.5    2.4    2.3
:Stinking Water Creek
Palisade 2NW          2.7    2.6    2.6    2.4    2.3    2.2    2.2
:Niobrara River
Sparks                2.7    2.7    2.6    2.6    2.5    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 second 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 outlook
scheduled outlook will be issued toward the end of this month.

$$

Brooks


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