Text Products for ESF Issued by LBF

Flood Potential Outlook
Issued by NWS North Platte, NE
Versions: 1 2
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Probabilistic Hydrologic Outlook
National Weather Service North Platte NE
944 AM CST Thu Feb 29 2024

...Spring Flood and Water Resource Outlook Number 2...

...A Below Average Flood Potential from Ice Jams and Spring
Snowmelt...

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 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.

.Flood Outlook Summary...
A below average flood potential is expected from spring snowmelt and
ice jams. No snow cover currently exists across western and north
central Nebraska. Rivers are currently ice free. Temperatures have
remained above normal the last two weeks of February. Ice jams are
not expected on rivers, unless colder temperatures return.

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

.Snow Cover and Mountain Snowpack...
As of February 29th, no snow cover existed across western and north
central Nebraska. March and April are typically snowy months, so
additional snowfall is possible.

Snowpack conditions in the North Platte and South Platte River
Basins in Colorado and Wyoming are currently below average. Snow
water equivalents ranged from near 95 percent of average for the
North Platte Basin and 93 percent of average for the South Platte
Basin. These values are below last year. A below average flood
potential is expected from mountain snowmelt runoff.

.Reservoir Conditions...
Normal operations are ongoing at reservoirs along the North Platte
River for this time of year. Releases from these dams have been
limited through the winter months, with inflows generally coming
from melting snow. Because of these operations, reservoir levels
have risen though the winter months. The current reservoir storage
across Wyoming, as well as Lake McConaughy, are below average for
this time of year.

.Soil Conditions and Frost Depths...
Soil moisture was near normal to below normal across the southeast
panhandle and southwest Nebraska to above to much above normal
across north central Nebraska. According to the U.S. Drought
Monitor, abnormally dry conditions remained across far southwest
Nebraska, which includes the Frenchman Creek Basin. Otherwise, no
drought conditions currently exist. As of February 29th, soil
temperature sensors indicate 4 inch soil temperatures range from 32
to 37 degrees, with some frost in the top three inches reported.

.River and Lake Ice Conditions...
Monthly average streamflow was average to above average across the
central and northern Sandhills, including the Niobrara, Elkhorn and
Loup River Basins. Average to much below average streamflow was
indicated across the southeast panhandle and southwest Nebraska,
including the Platte River Basin, and Frenchman Creek Basin. Lakes
and rivers were currently ice free.

.Seasonal Precipitation...
Precipitation so far this water year, since October 1, 2023, has
ranged from near normal to below normal across the southeast
panhandle into west central and southwest Nebraska to much above
normal across Custer County northward across the eastern half of
north central Nebraska. These areas which received from 5 to 11
inches, were from 130 to over 200 percent of normal.

.Weather Outlooks...
Water temperatures in the tropical Pacific Ocean remain above
average, with El Nino conditions. The outlook indicates weak
El Nino conditions will persist into March and April. For the late
winter and spring months, this weather pattern will typically favor
near normal temperatures with above normal precipitation across the
Central Plains.

According to the Climate Prediction Center, as of February 29th, the
latest 8 to 14 day outlook calls for above average temperatures with
above average precipitation.

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

The latest 90 day outlook for March, April and May indicates
near average temperatures with near average precipitation going
into this spring.

.Numerical Weather Outlooks...

For the Frenchman Creek, North Platte, South Platte, Platte,
Elkhorn, and Niobrara Rivers...long range probabilistic outlooks
are issued for the water year from December through May. 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:  03/02/2024  - 05/31/2024

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:North Platte River
Lisco                4.0    5.0    6.0 :   6   11   <5   <5   <5   <5
Lewellen             8.0    9.0   10.0 :  12   14   <5   <5   <5   <5
North Platte         6.0    6.5    7.0 :   9   16    6   13    6   12
:South Platte River
Roscoe               9.0   11.0   13.0 :  12   13    8    8    7    7
North Platte        13.0   14.0   15.0 :   8    8    7    7    5   <5
: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 :  21   26   14   14    6    7
:Frenchman Creek
Palisade             7.0    8.0    9.0 :  12   12   <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   12.0   16.0 :  <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: 03/02/2024  - 05/31/2024
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:North Platte River
Lisco                 1.7    1.8    1.9    1.9    2.3    3.5    4.1
Lewellen              6.4    6.4    6.5    6.6    7.1    8.2    8.5
North Platte          4.7    4.7    4.7    4.8    5.0    5.9    7.4
:South Platte River
Roscoe                4.6    4.6    4.8    6.6    8.5    9.2   13.9
North Platte          7.0    7.0    7.2    8.4   10.7   11.3   15.1
:Elkhorn River
Ewing 1N              2.9    2.9    3.1    5.0    6.5    8.2    8.8
:Platte River
Brady North Chann     2.0    2.3    3.0    5.1    7.1    9.2   11.3
:Frenchman Creek
Palisade              3.6    3.6    3.6    4.0    5.0    7.1    7.5
:Stinking Water Creek
Palisade 2NW          2.8    2.8    2.8    3.2    3.7    5.5    6.4
:Niobrara River
Sparks                3.1    3.2    3.2    3.4    3.7    4.1    4.4

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: 03/02/2024  - 05/31/2024
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:North Platte River
Lisco                 1.0    1.0    1.0    1.0    0.9    0.9    0.9
Lewellen              5.3    5.3    5.2    5.2    5.2    5.2    5.2
North Platte          4.6    4.6    4.5    4.5    4.5    4.5    4.5
:South Platte River
Roscoe                3.6    3.3    3.1    2.1    2.0    1.9    1.9
North Platte          6.9    6.8    6.8    6.8    6.7    6.7    6.7
:Elkhorn River
Ewing 1N              2.2    2.1    1.9    1.6    1.3    1.3    1.3
:Platte River
Brady North Chann     2.0    0.3    0.0    0.0    0.0    0.0    0.0
:Frenchman Creek
Palisade              3.6    3.6    3.5    3.5    3.4    3.4    3.4
:Stinking Water Creek
Palisade 2NW          2.5    2.4    2.3    2.1    0.0    0.0    0.0
:Niobrara River
Sparks                3.0    3.0    3.0    3.0    3.0    3.0    3.0

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 2024. The next spring flood outlook will be issued March 14th.
Thereafter, long-range probabilistic outlooks are issued near the
end of the month throughout the year.

$$

Roberg
National Weather Service Weather Forecast Office
