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FGUS73 KFGF 231751
ESFFGF

NDC005-027-071-281200-

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.

.OUTLOOK SUMMARY...

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
      outlook.

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%
--------            ------ ------ ------ ------ ------ ------ ------
Devils Lake.....
  CREEL BAY         1446.7 1446.6 1446.5 1446.4 1446.3 1446.3 1446.3
Stump Lake.....
  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.

.OUTLOOK SCHEDULE...

 - 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.

.ADDITIONAL INFORMATION...

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
  moisture.

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
  Services (AHPS).

A YouTube video on "How to Interpret River Outlook Products" is at:

         www.youtube.com/watch?v=pSoEgvsnpv4

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:

             water.weather.gov/ahps2/index.php?/wfo=fgf

Wind and wave forecasts for Devils and Stump lakes are available for
a 7-day period when the lakes are sufficiently ice-free at:

           www.weather.gov/fgf/lake_info

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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      weather.gov/fgf
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