Flood Potential Outlook
Issued by NWS Bismarck, ND

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NDC009-013-023-049-061-069-075-079-101-302200-

PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE BISMARCK ND
1018 AM CST THU FEB 16 2017

...SPRING FLOOD AND WATER RESOURCES OUTLOOK...

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

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 single greatest difference between this and the previous
release of these probabilistic tables is the noticeable increase
in flood risk for the Souris River near Sherwood. Outside of this
one location, probabilities remain mostly unchanged. A somewhat
encouraging aspect of the probability tables is the somewhat lower
risk of major flood stage being reached than what might have been
expected. This lower than expected risk of widespread major flooding
is at least partially due to the lack of significant frost depth
under the snow. This lack of frost depth will prove beneficial under
all but the most extreme of melt conditions by allowing a larger
than normal fraction of meltwater to infiltrate the unfrozen ground.

The take away message from this outlook is that there is clearly
enough snow-water equivalent in the Souris River basin to produce
widespread minor flooding and a slightly greater than normal risk
of producing moderate to major flooding. Snow accumulation has
tapered off from the record setting pace of early winter.
However...there has yet to be any significant loss of water in the
basin due to melting or sublimation, and by the end of March the
risk of spring rains begins to increase to compound runoff rates.

Importantly, none of the numbers below reflect the risk of ice-
related high water. Ice jams and associated high water are not
calculable in the models used which are based on flow in the river.

This Spring Flood and Water Resources Outlook will be issued again
with updated numbers on 2 March, 2017.

...Current Conditions...
Rivers, lakes, and reservoirs are at or below their prescribed
drawdown levels for this time of year. Alameda Reservoir in
Saskatchewan has increased its discharge in order to be able to
capture more of the spring runoff from its watershed. Snow cover
remains variable across the Souris River Basin with the heaviest
snowpack being in the southern and eastern part of its extent in
North Dakota. As one looks to the north the snowpack diminishes
to something near normal in the upper watershed above Rafferty
Dam and slightly above normal above Alameda Dam in Saskatchewan.

Soil moisture remains normal to well above normal across the
Souris River basin due to moisture late last fall.

Increased discharges out of Alameda and Lake Darling are already
working their way through the system. Again, this is being done
to create more storage in Alameda and also has the benefit of
starting to loosen and erode the ice cover on the Souris River.

...Weather Outlook...
The near term 6-10 and 8-14 day outlooks favor a well above
normal chance for warmer than normal temperatures and
precipitation. Looking out farther at the one-month outlook and
the region is still favored for above normal temperatures and
precipitation, although the beginning of March is expected to be
cooler than the end of February. Even farther out, the three-month
outlooks favor a cooler than normal outcome with a slight favoring
of above normal normal precipitation. This would suggest that March
and April will have to be fairly cool overall to overcome what is
expected to be a warm February.


...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: 02/19/2017 - 05/20/2017
                                       :    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    20   <5   13   <5    8   <5
Souris River
  Sherwood        1623.0 1625.0 1630.0    75   11   47   <5   <5   <5
  Foxholm         1573.0 1576.0 1578.0   >95   35  >95   13   28   <5
  Minot 4NW       1562.0 1565.0 1570.0    85   12   49    6   <5   <5
  Minot Brwy Brdg 1551.0 1553.0 1557.0    36    6   14   <5    7   <5
  Logan           1536.0 1538.0 1540.0    93   17   28    5   <5   <5
  Sawyer          1524.0 1526.0 1528.0    34    7    9   <5    7   <5
  Velva           1507.0 1512.0 1517.0    76   15    7   <5   <5   <5
Wintering River
  Karlsruhe       1509.0 1511.0 1512.0    65    6   <5   <5   <5   <5
Souris River
  Towner          1454.0 1456.0 1458.0   >95   55  >95   26   13    5
  Bantry          1440.0 1441.0 1443.0   >95   52  >95   37   26    6
Willow Creek
  Willow City     1442.0 1446.0 1448.0   >95   36   61   15   <5   <5
Souris River
  Westhope        1414.0 1418.0 1420.0   >95   44  >95   23   80   17
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: 02/19/2017 - 05/20/2017
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Des/ Lacs River
Foxholm             1646.3 1646.6 1647.3 1649.0 1650.5 1653.4 1654.7
:Souris River
Sherwood            1621.0 1621.5 1623.0 1624.8 1625.8 1627.1 1628.1
Foxholm             1576.1 1576.3 1576.7 1577.3 1578.1 1578.6 1579.6
Minot 4NW           1560.8 1561.5 1563.1 1564.8 1567.0 1568.0 1569.0
Minot Brwy Brdg     1546.5 1547.0 1548.0 1549.9 1552.2 1554.3 1559.5
Logan               1535.5 1536.4 1537.1 1537.5 1538.0 1538.4 1539.5
Sawyer              1520.9 1522.0 1522.7 1523.4 1524.5 1525.5 1528.6
Velva               1505.8 1506.4 1507.1 1508.0 1509.0 1509.7 1512.5
:Wintering River
Karlsruhe           1508.2 1508.4 1508.8 1509.3 1509.6 1509.8 1510.0
:Souris River
Towner              1456.4 1456.6 1456.9 1457.3 1457.7 1458.3 1460.2
Bantry              1441.8 1442.0 1442.2 1442.7 1443.0 1443.4 1444.5
:Willow Creek
Willow City         1444.7 1445.1 1445.6 1446.3 1446.8 1447.8 1447.9
:Souris River
Westhope            1418.3 1418.5 1420.3 1422.0 1423.1 1424.2 1427.0

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: 02/19/2017 - 05/20/2017
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
Des Lacs River
  Foxholm           1639.0 1639.0 1639.0 1639.0 1639.0 1639.0 1638.8
Souris River
  Sherwood          1605.5 1605.5 1605.5 1605.5 1605.5 1605.5 1605.5
  Foxholm           1566.6 1566.6 1566.6 1566.6 1566.6 1566.6 1566.6
  Minot 4NW         1550.7 1550.7 1550.7 1550.7 1550.7 1550.7 1550.7
  Minot Brwy Brdg   1537.1 1536.9 1536.8 1536.7 1536.7 1536.7 1536.7
  Logan             1519.8 1519.8 1519.8 1519.8 1519.8 1519.8 1519.8
  Sawyer            1506.6 1506.6 1506.6 1506.6 1506.6 1506.6 1506.6
  Velva             1490.2 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            1444.4 1444.4 1444.4 1444.4 1444.4 1444.4 1444.4
  Bantry            1430.4 1430.3 1430.3 1430.3 1430.3 1430.3 1430.3
Willow Creek
  Willow City       1436.0 1436.0 1436.0 1436.0 1436.0 1436.0 1436.0
Souris River
  Westhope          1409.6 1409.3 1409.1 1408.7 1408.6 1408.6 1408.6

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 2 March, 2017.

$$
ajs



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