Flood Potential Outlook
Issued by NWS Bismarck, ND

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FGUS73 KBIS 051934
ESFBIS

PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE BISMARCK ND
125 PM CST THU MAR 05 2015


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

This probability based Spring Flood and Water Resources Outlook is
for the Souris River Basin of North Dakota, covering the time period
of early March through early June.

The following message has four distinct sections. The first provides
text on the notable highlights of the probabilities found in this
outlook. The second gives the current probabilities based on
existing conditions (CS) and the normal, or historical (HS) risk of
those locations reaching their respective Minor, Moderate, or Major
flood categories. The third section provides the current
probabilities of the river reaching the listed stages. Finally, the
fourth section contains the probability of each site falling to the
specified levels.


...FLOOD OUTLOOK OVERVIEW HIGHLIGHTS...
Precipitation has been normal to below normal the past few weeks
since the original issuance of the Spring Flood and Water Resources
Outlook. What is notably missing so far is the accumulation of a
widespread, heavy snowpack. Accordingly, the probabilities contained
below are near normal to slightly below normal overall. This puts
the risk of widespread flooding across the Souris River Basin well
below that of recent years.

However, this does not suggest there is negligible or no risk of
flooding - only that it would take something well outside of
seasonally normal conditions this Spring to create widespread high
water. Indeed, there is enough snow water equivalent in the upper
Souris River Basin that will be generating runoff in late March.
This still presents a reasonable chance of at least minor flooding
if it combines runoff from local spring rains.

Rather than widespread high water due to strong runoff with the well
above normal temperatures expected during the second week of March,
the greater risk will be of moderate runoff entering ice covered
streams. This will result in higher water levels than one would
normally see for the amount of runoff. Ice jams and other ice
problems such as blocked culverts cannot be ruled out.


...CURRENT CONDITIONS...
Snowpack, or more precisely, the water equivalent in what little
snow is across the region, generally increases as one looks farther
north in the basin. Water equivalent in the Minot area is slightly
below normal at less than an inch, but as you get into the upper
portions of the Souris River Basin in Saskatchewan, snowpack is near
normal with around 1.5 - 2.1 inches of water equivalent.

All flood control reservoirs are at their preferred spring drawdown
levels in anticipation of needing this year`s snowmelt in order to
fill them to full operating levels.

Soil moisture content in the upper few inches remains high and the
surface of the ground is well frozen. Frost depths overall though
are not as unusually deep as observed the past few years.


...WEATHER OUTLOOK...
The near term 6 - 10 and 8 - 14 day outlooks call for a higher
probability of above normal temperatures and below normal
precipitation. Looking out at the longer 1-month and 3-month
outlooks, tend to prefer an equal chance of above normal, near
normal, or below normal temperatures and precipitation.


...SUMMARY OF HYDROLOGIC CONDITIONS AND RISKS...
The near term weather outlook strongly suggests we will be entering
the second week of March with the spring melting season in full
swing across the southern portion of the Souris River Basin. In
general, the relatively thin snowpack across this area will be
quick to ripen and begin producing runoff. This will not give the
smaller rivers and streams much time for the ice cover to
adequately deteriorate before snowmelt runoff makes its way into the
rivers.

The big question will be whether or not enough runoff makes it into
the rivers to lift the ice far enough for it to begin to break up
and mobilize. While river watchers may see only modest amounts of
water making its way into the rivers and streams, the solid sheet
of ice on the river itself will help elevate the actual water levels
as it impedes streamflow.

At this point, all current indicators suggest a low risk of
widespread flood problems along the Souris River in North Dakota.
Localized flooding due to untimely spring rains, along with ice
affected flow in the near term present the great majority of
concerns going forward.


...LONG-RANGE PROBABILISTIC RIVER OUTLOOK BY FLOOD CATEGORY...

The table below give both the Conditional Simulation (CS) risk of
flooding based on current condtions and the Historical Simulation
(HS) risk of flooding. Risks of reaching Minor, Moderat, and Major
flood categories are presented.



...LONG-RANGE PROBABILISTIC RIVER OUTLOOK BY FLOOD CATEGORY...


                           Souris River BASIN
                    LONG-RANGE PROBABILISTIC OUTLOOK
              VALID FROM MARCH 9, 2015  TO JUNE 7, 2015

The table below give both the Conditional Simulation (CS) risk of
flooding based on current condtions and the Historical Simulation
(HS) risk of flooding. Risks of reaching Minor, Moderat, and Major
flood categories are presented.


       PROBABILITIES FOR MINOR, MODERATE, AND MAJOR FLOODING
                      FROM  3/9/2015 TO 6/7/2015

TABLE 1                                  : CURRENT AND HISTORICAL
                                         : CHANCES OF EXCEEDING FLOOD
                                         : CATEGORY IN PERCENT (%)
                         CATEGORICAL     :
                      FLOOD STAGES (FT)  :  MINOR   MODERATE  MAJOR
LOCATION            MINOR    MOD   MAJOR :  CS HS    CS HS    CS HS
--------            ------ ------ ------ : --- ---  --- ---  --- ---
Des Lacs River.....
  Foxholm             16.0   18.0   19.0 :  <5  <5   <5  <5   <5  <5
Souris River.....
  Sherwood            18.0   20.0   25.0 :  <5   6   <5  <5   <5  <5
  Souris nrFoxholm    10.0   13.0   15.0 :  67  55   36  41   <5  <5
  Minot 4NW           14.0   17.0   22.0 :   6  16   <5  <5   <5  <5
  Minot             1549.0 1551.0 1555.0 :  <5  <5   <5  <5   <5  <5
  Logan               34.0   36.0   38.0 :  12  21   <5  10   <5  <5
  SAWYER              22.0   24.0   26.0 :  <5   9   <5  <5   <5  <5
  VELVA             1505.0 1510.0 1515.0 :   9  20   <5  <5   <5  <5
Wintering River.....
  Karlsruhe            7.0    9.0   10.0 :  <5  12   <5  <5   <5  <5
Souris River.....
  Towner              52.0   54.0   56.0 :  67  66   36  46   <5  10
  Bantry              11.0   12.0   14.0 :  53  64   38  49   <5   9
Willow Creek.....
  Willow City         10.0   14.0   16.0 :  32  38   <5  16   <5  <5
Souris River.....
  Westhope            10.0   14.0   16.0 :  38  52   <5  24   <5  18

LEGEND:
    CS  =  Conditional Simulation
    HS  =  Historical Simulation
    FT  =  Feet above gage zero datum



...LONG-RANGE PROBABILISTIC OUTLOOK BY RIVER STAGE...

                          SOURIS RIVER BASIN
                    LONG-RANGE PROBABILISTIC OUTLOOK


The table below gives the current 95 through 5 percent probabilities
for exceeding river stages at the listed Forecast Points during the
valid period of this outlook.

For example: During the valid time period, there is a 50% chance for
             the Des Lacs River near Foxholm to rise above a
             stage of 6.8 ft and only a 10% chance it will rise
             above a stage of 9.7 ft.


           PROBABILITIES FOR EXCEEDING LISTED RIVER STAGES
                      FROM  3/9/2015 TO 6/7/2015
TABLE 2

LOCATION              95%    90%    75%    50%    25%    10%    05%
--------             -----  -----  -----  -----  -----  -----  -----
Des Lacs River.....
  Foxholm              5.8    5.8    6.1    6.8    7.7    9.7   11.7
Souris River.....
  Sherwood             8.8    9.4   10.5   12.2   16.0   16.8   17.2
  Souris nrFoxholm    8.0    8.3    9.5   11.8   13.9   14.3   14.4
  Minot 4NW           5.9    6.1    7.3    9.1   12.4   13.7   14.3
  Minot             1541.5 1541.5 1542.0 1542.8 1544.5 1545.1 1545.5
  Logan               23.5   23.8   25.5   28.0   32.3   34.5   35.1
  SAWYER               9.3    9.4   11.0   13.9   18.1   19.9   21.5
  VELVA             1492.3 1493.0 1495.0 1498.5 1503.6 1504.8 1506.1
Wintering River.....
  Karlsruhe            2.8    2.8    2.9    3.1    3.5    4.7    6.0
Souris River.....
  Towner              48.5   48.8   50.9   52.9   54.5   55.1   55.6
  Bantry               6.5    6.8    8.7   11.2   12.5   13.0   13.4
Willow Creek.....
  Willow City          5.2    5.3    5.6    6.2   11.4   13.1   14.1
Souris River.....
  Westhope             7.8    8.1    8.6    9.1   10.9   12.5   15.1



...LONG-RANGE PROBABILISTIC OUTLOOK BY RIVER STAGE...


                          SOURIS RIVER BASIN
                    LONG-RANGE PROBABILISTIC OUTLOOK

The table below represents the likelihood of the river remaining
above the listed stages.

For example: The Des Lacs River near Foxholm has a 95% chance the
             river will remain above 4.7 ft and only a 5% chance it
             will fall below 4.5 ft.


              PROBABILITIES FOR FALLING BELOW LISTED RIVER STAGES
                             3/9/2015 - 6/7/2015

TABLE 3

LOCATION              95%    90%    75%    50%    25%    10%    05%
--------             -----  -----  -----  -----  -----  -----  -----
Des Lacs River.....
  Foxholm              4.7    4.7    4.7    4.6    4.6    4.5    4.5
Souris River.....
  Sherwood             0.6    0.6    0.6    0.6    0.6    0.6    0.6
  Souris nr Foxholm    4.5    4.5    4.5    4.5    4.5    4.5    4.5
  Minot 4NW            3.9    3.9    3.9    3.9    3.9    3.8    3.8
  Minot             1536.2 1536.2 1536.2 1536.2 1535.7 1535.4 1534.9
  Logan               18.7   18.7   18.7   18.7   18.7   18.5   18.5
  SAWYER               5.5    5.5    5.5    5.5    5.4    5.3    5.3
  VELVA             1489.0 1489.0 1489.0 1489.0 1489.0 1489.0 1489.0
Wintering River.....
  Karlsruhe            1.6    1.6    1.6    1.6    1.6    1.6    1.6
Souris River.....
  Towner              43.9   43.9   43.8   43.7   43.6   43.3   43.2
  Bantry               2.1    2.0    2.0    1.9    1.8    1.7    1.7
Willow Creek.....
  Willow City          4.6    4.6    4.6    4.6    4.6    4.6    4.6
Souris River.....
  Westhope             6.3    6.3    6.3    6.3    6.0    5.9    5.8


...THE OUTLOOK PRODUCTION PROCESS...
This long-range probabilistic outlook is based on a series of peak
river levels, or crests, takeing from the forecast hydrograph results
of the NWS Ensemble Streamflow Prediction Model (ESP). The model
is run for multiple scenarios starting at current river, snow, and
soil conditions using 25 or more years of past precipitation and
temperature conditions in the historical record. These crests can
then be ranked from lowest to highest, and assigned an exceedance
probability. For example, using a series of 50 years, the lowest
ranked cerst has 49 crests above it. As 95% of the crests are above
this value, it is assigned a 95% Probability Of Exceedance (POE).

The probabilities can be used for risk management by comparing this
year`s current temperature and preciptitation outlooks with those
of past year used in the hydrologic outlook. They can also be used
as an indication of the range of crests expected during the valid
period of the outlook.

By providing a range of peak river level probabilities, the NWS is
contributing to the region`s Impact-Based Decision Support Services
that help with long-range flood planning and response readiness.
This outlook is a part of the National Weather Service`s Advanced
Hydrologic Prediction Services (AHPS).

This outlook was produced using precipitation and temperatures for
the years 1948 through 2011.


...ADDITIONAL INFORMATION SOURCES...
The AHPS long-range probabilistic hydrologic outlooks are issued
near the end of each month. However, the Spring Flood and Water
Resources Outlooks are issued several times in advance of the
critical spring melt season starting in mid-lake February and
going through Marck...or until the melt season is in full effect.

This outlook is also available in graphic form on the NWS website
along with explanations that help in interpreting them. They are
available at:

        WWW.WEATHER.GOV/BISMARCK OR WEATHER.GOV/BIS

Click on the "Rivers and Lakes" tab above the map, or the AHPS
link in the blue banner on the left side of the screen.

Current river conditions for all forecast points are available
on our website, as well as forecast when the location is near or
above flood stage.

If you have any questions, contact the NWS at 701-250-4495.

$$
AJS




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