Flood Potential Outlook
Issued by NWS Bismarck, ND

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PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE BISMARCK ND
1140 AM CDT THU JUN 28 2018

...FLOOD AND WATER RESOURCES OUTLOOK...

This probability based Flood and Water Resources Outlook is
for the Souris (Mouse) River basin of North Dakota and covers the
period of late June through late August.

The following message has four sections. The first provides some text
on the highlights of this outlook and conditions affecting the local
hydrology. The second section gives the current and normal/historical
risks of flooding as determined by the Ensemble Streamflow Forecast
model of the National Weather Service. The third section gives the
current probabilities for reaching flood stage at the listed forecast
locations. And finally, the fourth section covers the risk of the
river sites falling below the listed stages.

...Flood Outlook Highlights...
The general threat of widespread river flooding is best thought of as
near normal for the Souris River basin. Despite lengthy dry spells,
recent rains have brought soil moisture values up enough to help
encourage runoff in heavier rain events. However, given the season,
any problematic high water should be relatively isolated and minor in
nature.

...Current Conditions...
Lake Darling, Rafferty Reservoir, and Grant Devine (formerly
known as Alameda Reservoir) are well within their normal ranges
for this time of year. Small rivers also remain slightly below normal
to near normal for this time of year. Wetlands, after a dry 2017, tend
to be slightly lower than recent years at this point even though some
small areas have seen the wetlands rebound back to high levels due to
late spring rains. Similarly, soil moisture levels are below normal
to well below normal across wide areas even though localized heavy
rains have improved the overall soil moisture outlook during the past
few weeks.

...Weather Outlook...
The near term 6-10 and 8-14 day outlooks depict a well above
normal chance for warmer than normal temperatures with above normal
precipitation. The one-month and three-month outlooks put the area
in the equal chances category for either above normal, near normal,
or below normal temperatures and precipitation.

...Important Note On Substantive Changes...
Beginning January 1st of 2016, the National Weather Service converted
all river gage data in the Souris River basin of North Dakota to feet
above Mean Sea Level using the North American Vertical Datum of 1988.
This included raises in flood stage definitions by up to one foot at
individual locations in order to continue working with whole numbers.
More information on this can be had by contacting Service Hydrologist
Allen Schlag at 701-250-4495.

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 of the model
predicting a rise to 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: 07/01/2018 - 09/29/2018
                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
Des Lacs River
  Foxholm         1651.0 1653.0 1654.0    <5   <5   <5   <5   <5   <5
Souris River
  Sherwood        1623.0 1625.0 1630.0    <5   <5   <5   <5   <5   <5
  Foxholm         1573.0 1576.0 1578.0    <5   <5   <5   <5   <5   <5
  Minot 4NW       1562.0 1565.0 1570.0    <5   <5   <5   <5   <5   <5
  Minot Brwy Brdg 1551.0 1553.0 1557.0    <5   <5   <5   <5   <5   <5
  Logan           1536.0 1538.0 1540.0    <5   <5   <5   <5   <5   <5
  Sawyer          1524.0 1526.0 1528.0    <5   <5   <5   <5   <5   <5
  Velva           1507.0 1512.0 1517.0    <5   <5   <5   <5   <5   <5
Wintering River
  Karlsruhe       1509.0 1511.0 1512.0    <5   <5   <5   <5   <5   <5
Souris River
  Towner          1454.0 1456.0 1458.0    <5   10   <5   <5   <5   <5
  Bantry          1440.0 1441.0 1443.0    <5   10   <5   <5   <5   <5
Willow Creek
  Willow City     1442.0 1446.0 1448.0     5    8   <5   <5   <5   <5
Souris River
  Westhope        1414.0 1418.0 1420.0    <5    9   <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: 07/01/2018 - 09/29/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Des Lacs River
Foxholm             1639.6 1639.6 1639.6 1639.6 1640.9 1641.3 1642.9
:Souris River
Sherwood            1606.5 1606.5 1606.8 1607.9 1610.0 1612.4 1615.6
Foxholm             1566.5 1566.5 1566.5 1568.1 1569.9 1570.9 1571.1
Minot 4NW           1551.1 1551.1 1551.1 1551.9 1553.0 1554.1 1554.6
Minot Brwy Brdg     1538.6 1538.6 1538.7 1541.7 1542.7 1543.1 1543.2
Logan               1520.1 1520.1 1520.2 1522.6 1524.7 1526.3 1527.2
Sawyer              1507.3 1507.3 1507.4 1508.9 1510.5 1511.8 1512.7
Velva               1490.9 1490.9 1491.1 1492.6 1493.6 1495.8 1496.7
:Wintering River
Karlsruhe           1502.8 1502.8 1502.9 1503.6 1504.2 1504.9 1505.1
:Souris River
Towner              1447.3 1447.3 1447.3 1447.3 1449.5 1452.1 1452.9
Bantry              1433.0 1433.0 1433.0 1433.1 1435.3 1437.5 1438.7
:Willow Creek
Willow City         1436.0 1436.0 1436.0 1436.4 1436.7 1437.6 1442.1
:Souris River
Westhope            1410.4 1410.4 1410.4 1410.4 1411.0 1411.9 1412.7

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: 07/01/2018 - 09/29/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
Des Lacs River
  Foxholm           1639.2 1639.2 1639.2 1639.1 1639.1 1639.1 1639.1
Souris River
  Sherwood          1606.2 1606.0 1605.5 1605.5 1605.5 1605.5 1605.5
  Foxholm           1566.5 1566.5 1566.5 1566.5 1566.5 1566.5 1566.5
  Minot 4NW         1551.0 1550.9 1550.9 1550.8 1550.8 1550.8 1550.8
  Minot Brwy Brdg   1538.3 1537.7 1537.4 1537.1 1537.0 1536.9 1536.9
  Logan             1520.1 1520.0 1519.9 1519.9 1519.8 1519.8 1519.8
  Sawyer            1507.1 1506.7 1506.7 1506.6 1506.6 1506.6 1506.6
  Velva             1490.6 1490.2 1490.2 1490.2 1490.2 1490.2 1490.2
Wintering River
  Karlsruhe         1502.8 1502.8 1502.8 1502.8 1502.8 1502.8 1502.8
Souris River
  Towner            1445.0 1444.4 1444.4 1444.4 1444.4 1444.4 1444.4
  Bantry            1431.1 1430.8 1430.8 1430.7 1430.7 1430.7 1430.7
Willow Creek
  Willow City       1435.5 1435.5 1435.5 1435.5 1435.5 1435.5 1435.5
Souris River
  Westhope          1409.7 1409.3 1409.2 1409.2 1409.2 1409.2 1409.2

These long-range probabilistic outlooks contain forecast values that
are calculated using historical conditions from 30 or more years of
climatological data, and 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/bis for more weather and water
information.

The next outlook will be issued on July 26th.

$$
ajs



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