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FGUS73 KFGF 231751
Probabilistic Hydrologic Outlook
National Weather Service Grand Forks ND
1247 PM CDT Thu Sep 23 2021
...DEVILS LAKE OUTLOOK FOR FLOOD POTENTIAL...
Devils and Stump Lakes
Long-Range Probabilistic Outlook
The National Weather Service provides long-range probabilistic
hydrologic outlooks for Devils and Stump lakes between January
and September. They will not be provided between October and
December. Depending on the season, the high or low water
probabilities may be omitted due to their applicability to
the hydrologic situation.
Note: The August and September non-exceedance outlooks incorporated
a daily average of 75 cfs worth of pumping operations on Devils Lake
through the end of September. The June and July non-exceedance
outlooks incorporated a daily average of 200 cfs worth of pumping
operations through the end of October.
Since the last outlook issuance on August 26th, much of the area
received additional, and much needed, precipitation. Amounts for
this time period were near to above normal for much of the basin but
still slightly below normal across northern reaches of the basin.
This precipitation did help improve drought conditions slightly over
the course of the last month. Although the heart of the basin
remains in the Extreme Drought category, some of the area has seen
improved conditions and is now classified as Severe Drought.
Additionally, any mention of Exceptional Drought has been removed
for most of the state of North Dakota. All in all, recent
precipitation and drought improvement has led to very little change
in the non-exceedance numbers with this outlook as compared to the
August 2021 outlook.
Climate outlooks for the end of September and into the beginning of
October indicate above normal temperatures and below normal
precipitation to return. The above normal temperatures look to
continue through the remainder of the fall but by winter, equal
chances for above, below, or near normal temperatures and
precipitation are forecast.
.Chances of Devils and Stump Lakes Rising Above Given Lake Levels...
The probability of exceeding a given lake level is the percentage
of maximum lake level rises that are above that level for all the
years that were run through the model using the precipitation
and temperatures for those years during the valid period of the
Exceedance information is not published in September.
.Chances of Devils and Stump Lakes Falling Below Given Lake Levels...
The probability of not exceeding a given lake level is the
percentage of lake level falls that are below that level for
all the years that were run through the model using the
precipitation and temperatures for those years during the
valid period of the outlook.
Interpretation Aid: There is a 50 percent chance that Devils
Lake will fall below 1446.4 feet during the valid period and
only a 5 percent chance that it will fall below 1446.3 feet.
Probabilities for Non-Exceeding Listed Lake Levels
FROM SEPTEMBER 20, 2021 TO DECEMBER 26, 2021
LOCATION 95% 90% 75% 50% 25% 10% 05%
-------- ------ ------ ------ ------ ------ ------ ------
CREEL BAY 1446.7 1446.6 1446.5 1446.4 1446.3 1446.3 1446.3
EAST STUMP LAKE 1446.7 1446.6 1446.5 1446.4 1446.3 1446.3 1446.3
The non-exceedance value for a listed percentage is the value
where that percentage of all model cases run were below that
lake level for the specified valid period of the outlook.
- Between January and May, only the high water exceedances will be
provided with valid periods ending at the end of September.
- Special Spring Flood and Water Management Outlooks will be issued
in late February and early March.
- For June and July, both high-water and low-water exceedances
will be provided.
- For August and September, only the low-water exceedances will be
provided with valid periods ending at the end of November.
- No probability of exceedance/non-exceedance information will be
given from October through December, since lake freeze-up
levels will be given in the fall outlooks previously issued.
The long-range probabilistic outlook is based on high and low lake
levels that were calculated for the valid period using multiple
scenarios of temperature and precipitation from 1949 to 2018 and
current conditions of the lake, snowcover (in winter), and soil
By providing the complete range of lake level probabilities, the
amount of risk associated with long-range planning decisions can
be determined. These probabilistic outlooks are part of NOAA`s
National Weather Service`s Advanced Hydrologic Prediction
A YouTube video on "How to Interpret River Outlook Products" is at:
This outlook is also presented as probability graphs of lake height
for the full period as well as weekly probabilities. The outlook
graphics and explanations that help in interpreting these outlooks
are available on the NWS Grand Forks AHPS web page at:
Wind and wave forecasts for Devils and Stump lakes are available for
a 7-day period when the lakes are sufficiently ice-free at:
If you have any questions, contact the NWS at 701-772-0720.
You can follow us on Facebook at www.facebook.com/NWSGrandForks
and on Twitter at @NWSGrandForks.
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