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Winter Storm To Impact Parts Of The Ohio Valley and Great Lakes To Northern New England

A developing winter storm will sweep up through the Northeastern quadrant of the U.S. over the next two days. A swath of heavy snow will be followed by lake effect snow from parts of the Ohio Valley and Great Lakes to northern New England. Also, locally heavy rain will be possible across portions of the Northeast, while a potential line of strong thunderstorms may roll through the Mid-Atlantic. Read More >

Probabilistic Hydrologic Outlook
National Weather Service Bismarck ND
1030 AM CST THU FEB 13 2020

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

This Spring Flood and Water Resources Outlook is for the Souris
(Mouse) River basin of North Dakota, and covers the period of
mid-February through middle of May. This outlook is the first in
the Spring Flood and Water Resources Outlook series and will be
updated on 27 February and 13 March. After those updates, the NWS
will revert back to the regular monthly issuance on the fourth
Thursday of each month.

The following message has four sections. The first provides some
discussion 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...
Most locations across the Souris River basin of North Dakota are near
normal for flood risk during the spring melt season. However, the risk
of flooding increases substantially for the Souris near Towner,
Bantry, and Westhope. Similarly, Willow Creek near Willow City has
a significantly above normal risk of flooding this spring. The reason
for this disparity across the Souris River Basin of North Dakota is
the difference in snow-water equivalent (SWE). The snowpack above
Minot and Lake Darling is unremarkable and generally contains less
than one inch of SWE. As one approaches the eastern side of the basin
in North Dakota, the SWE content of the snowpack ranges from one to
two inches. While this is not necessarily an unusually high amount of
SWE going into spring, soil conditions tend to be much wetter than
normal and these wetter soils will inhibit infiltration and enhance
runoff during the spring melt season.

...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. The wet fall has generally put the soil
moisture above the 95th percentile. While this high soil moisture
extends into the Souris River Basin in Canada, the snowpack is
not significant with generally less than an inch of SWE above
Lake Darling. In the Towner and up through the Willow Creek
basin, a slightly greater snowpack exists with between one and two
inches of water available for the spring melt season.

...Weather Outlook...
The near term 6-10 and 8-14 day outlooks suggest a continuation of
the very benign weather pattern the area has experienced over the
past few weeks. This below normal precipitation pattern and near
normal to above normal temperatures will help lower flood risks
even more as we go into March. Looking farther into the future, the
3-month outlooks suggest a slightly cooler and wetter than normal
pattern for the entire February, March, and April period.

...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 stage
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 greater 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:
                    Valid  Period: 02/17/2020 - 05/17/2020
                                       :    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
Foxholm           1651.0 1653.0 1654.0 :   6   <5    5   <5   <5   <5
:Souris
Sherwood          1623.0 1625.0 1630.0 :  <5   11   <5   <5   <5   <5
Foxholm           1573.0 1576.0 1578.0 :  21   35   <5   12   <5   <5
Minot             1562.0 1565.0 1570.0 :   7   11    7    5   <5   <5
Minot             1551.0 1553.0 1557.0 :   6   <5   <5   <5   <5   <5
Logan             1536.0 1538.0 1540.0 :  10   17    7   <5   <5   <5
Sawyer            1524.0 1526.0 1528.0 :   7    7    6   <5   <5   <5
Velva             1507.0 1512.0 1517.0 :  12   15   <5   <5   <5   <5
:Wintering
Karlsruhe         1509.0 1511.0 1512.0 :  18    6   <5   <5   <5   <5
:Souris
Towner            1454.0 1456.0 1458.0 : >95   55   51   24    7   <5
Bantry            1440.0 1441.0 1443.0 : >95   51   92   37    7   <5
:Willow Creek
Willow City       1442.0 1446.0 1448.0 : >95   35   18   13   <5   <5
:Souris
Westhope          1414.0 1418.0 1420.0 : >95   45   65   23   32   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: 02/17/2020 - 05/17/2020
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Des Lacs
Foxholm            1641.9 1642.1 1642.8 1643.9 1645.7 1647.5 1653.0
:Souris
Sherwood           1608.7 1608.9 1611.3 1615.9 1619.0 1620.3 1620.9
Foxholm            1569.5 1569.7 1570.3 1570.8 1572.8 1573.9 1575.6
Minot 4NW          1554.0 1554.5 1555.0 1555.6 1556.7 1558.1 1567.0
Minot Brdwy Brdg   1543.1 1543.3 1543.4 1543.8 1544.4 1545.6 1552.8
Logan              1527.6 1528.5 1529.3 1530.2 1532.2 1535.7 1538.4
Sawyer             1514.7 1515.7 1516.6 1517.6 1519.7 1522.6 1526.4
Velva              1500.6 1501.7 1502.6 1504.0 1505.7 1507.5 1510.7
:Wintering
Karlsruhe          1507.7 1507.8 1508.0 1508.4 1508.9 1509.1 1509.4
:Souris
Towner             1455.0 1455.4 1455.6 1456.0 1456.6 1457.2 1459.1
Bantry             1440.7 1441.1 1441.2 1441.5 1441.9 1442.5 1443.8
:Willow Creek
Willow City        1443.0 1443.1 1444.0 1445.0 1445.7 1446.7 1447.5
:Souris
Westhope           1415.5 1415.7 1417.2 1419.0 1420.2 1421.6 1425.1

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: 02/17/2020 - 05/17/2020
LOCATION              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Des Lacs
Foxholm            1640.2 1640.2 1640.2 1640.1 1639.8 1639.7 1639.7
:Souris
Sherwood           1605.5 1605.5 1605.5 1605.5 1605.5 1605.5 1605.5
Foxholm            1567.2 1566.7 1566.5 1566.5 1566.5 1566.5 1566.5
Minot 4NW          1551.6 1551.6 1551.5 1551.4 1551.3 1551.2 1551.2
Minot Brdwy Brdg   1541.2 1541.2 1540.9 1540.2 1539.5 1539.2 1539.1
Logan              1522.5 1522.5 1522.4 1521.9 1521.1 1520.9 1520.7
Sawyer             1509.0 1509.0 1508.9 1508.4 1508.0 1507.9 1507.8
Velva              1492.5 1492.5 1492.5 1492.2 1491.8 1491.7 1491.5
:Wintering
Karlsruhe          1505.8 1505.8 1505.7 1505.7 1505.5 1505.4 1505.3
:Souris
Towner             1444.5 1444.5 1444.4 1444.4 1444.4 1444.4 1444.4
Bantry             1430.7 1430.5 1430.4 1430.2 1430.2 1430.1 1430.1
:Willow Creek
Willow City        1436.0 1436.0 1436.0 1436.0 1436.0 1436.0 1436.0
:Souris
Westhope           1411.3 1411.3 1411.3 1411.1 1410.1 1409.5 1409.5

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/bis for more weather and water
information.

The next outlook will be issued February 27.