Flood Potential Outlook
Issued by NWS Pueblo, CO

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Probabilistic Hydrologic Outlook
National Weather Service Pueblo CO
300 PM MST Thu Feb 16 2017

...Spring Flood and Water Resources Outlook...

This outlook is for the Arkansas River Basin in southeast Colorado
and the Rio Grande Basin in south central Colorado.

...The Potential for Spring Flooding...from Snowmelt Alone...is Near
Average in the Arkansas Basin...
...The Potential for Spring Flooding...from Snowmelt Alone...is Near
Average in the Rio Grande Basin...

This outlook is valid from February 16 2017 to March 2 2017.

...Outlook for the Arkansas Basin...

The flood potential in the Arkansas Basin, from snowmelt alone, is
near average.  Any snowmelt flooding, if it were to develop, would
most likely be minor, resulting in minimal or no property damage
but some public threat or inconvenience.

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 a 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  01/26/2017 - 04/26/2017

                                    : 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
--------          ----- ----- ----- : ---- ---- ---- ---- ---- ----

:Arkansas River
LEDC2             9.0   10.0   12.0    <5   <5   <5   <5   <5   <5
SALC2             8.0    9.0   10.0    <5   <5   <5   <5   <5   <5
WSVC2             9.0   10.0   11.0    <5   <5   <5   <5   <5   <5
PDLC2             9.0   10.0   11.0    <5   <5   <5   <5   <5   <5
CNCC2            10.0   12.0   14.0    <5   <5   <5   <5   <5   <5
PRTC2             9.0   10.0   11.0    <5   <5   <5   <5   <5   <5
PDAC2             8.0    9.0   11.0    <5   <5   <5   <5   <5   <5
ADLC2             7.0    8.0    9.0    <5   <5   <5   <5   <5   <5
NPTC2            16.5   17.5   18.5    <5   <5   <5   <5   <5   <5
CDMC2             8.0    9.0   10.0    <5   <5   <5   <5   <5   <5
ARCC2            10.0   11.0   12.0    <5   <5   <5   <5   <5   <5
LXHC2            11.0   13.0   15.0    <5   <5   <5   <5   <5   <5
LMAC2            11.0   13.0   15.0    <5   <5   <5   <5   <5   <5

:Fountain Creek
FNEC2            11.5   16.0   18.0    <5   <5   <5   <5   <5   <5
FHAC2             8.0   10.0   12.0    <5   <5   <5   <5   <5   <5
PNNC2            12.0   14.0   15.0    <5   <5   <5   <5   <5   <5
FCHC2            10.0   12.0   13.5    <5   <5   <5   <5   <5   <5

:St. Charles River
SCVC2            12.0   15.0   18.0    <5   <5   <5   <5   <5   <5

:Purgatoire River
PGMC2             7.0    9.0   11.0    <5   <5   <5   <5   <5   <5
PGRC2            10.0   12.0   14.0    <5   <5   <5   <5   <5   <5
PTRC2            11.0   12.0   13.0    <5   <5   <5   <5   <5   <5
LAPC2             9.0   12.0   15.0    <5   <5   <5   <5   <5   <5

Legend
CS  = Conditional Simulation (current outlook)
HS  = Historical Simulation
FT  = Feet

From the table above, it can be seen that the chance of exceeding
flood stage during the period (CS) is generally the same as the
historical chance (HS) at nearly all locations.  Consequently, the
threat of snowmelt flooding in the Arkansas Basin is near average.

Any snowmelt flooding at any of the points, if it were to develop,
would most likely be minor, resulting in minimal or no property
damage but some public threat or inconvenience.

Snowmelt flooding should not be confused with other types of
flooding that are associated with heavy storm runoff.  This outlook
does not address that type of flood potential.  Flooding and flash
flooding associated with heavy rainfall is always a possibility.

...Outlook for the Rio Grande Basin...

The flood potential in the Rio Grande Basin, from snowmelt alone, is
near average.  Any snowmelt flooding, if it were to develop, would
most likely be minor, resulting in minimal or no property damage but
some public threat or inconvenience.

Probabilities of exceeding various river stages as presented for the
Arkansas Basin above are not currently available for the Rio Grande
Basin.  However, a qualitative assessment of the flood potential on
the Rio Grande is provided here.

Snowpack in the Rio Grande Basin is running 146 percent of median.
Overall reservoir storage is running 89 percent of average. Although
snowpack is above average, there is currently not enough water in
the snow to raise the threat of snowmelt flooding beyond normal
levels.  Consequently, the threat of snowmelt flooding in the Rio
Grande Basin is near average.

Any snowmelt flooding, if it were to develop, would most likely be
minor, resulting in minimal or no property damage but some public
threat or inconvenience.

Snowmelt flooding should not be confused with other types of
flooding that are associated with heavy storm runoff.  This outlook
does not address that type of flood potential.  Flooding and flash
flooding associated with heavy rainfall is always a possibility.

...Flood Assessment Qualifier...

These flood potential assessments are based on current conditions
and projections of average temperature and precipitation for the
coming months.  It does not reflect the flood potential should more
extreme weather conditions develop.  If unusually warm or wet
conditions develop over the region during the period, then much more
severe flooding could occur.

...Summary of Past...Present and Future Conditions...

Temperatures have generally been 1 to 3 degrees above average across
the mountainous portion of the Arkansas Basin during the winter
months.  Temperatures across the mountainous portion of the Rio
Grande Basin have been about 2 to 4 degrees above average.

Overall snowpack levels are running above average across both the
Arkansas and Rio Grande Basins.  In both basins, the snowpack was
at 146 percent of median.

Precipitation is running above average across both the Arkansas and
Rio Grande Basins.  The mountains of the Arkansas Basin have
recorded 117 percent of average precipitation overall. The mountains
of the Rio Grande Basin have recorded 112 percent of average
precipitation.

Overall reservoir storage levels are running near average across
southeast Colorado and below average across south central Colorado.
Combined reservoir storage levels in the Arkansas Basin are around
99 percent of average, while combined levels in the Rio Grande Basin
are around 89 percent of average.

The outlook for March, April and May, from the National Weather
Service Climate Prediction Center, indicates that precipitation will
most likely be near or below average, while temperatures will most
likely be above average.

...Explanation of Contents...

This long range outlook contains forecast values that are calculated
using multiple season scenarios from 50 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 the complete range of probabilities,
the level of risk associated with long range planning decisions can
be determined.  These forecasts are part of the National Weather
Services Advanced Hydrologic Prediction Service.

...Schedule of Outlooks...

This is the first of 2 scheduled Spring Flood and Water Resources
Outlooks for 2017.  The second scheduled outlook will be issued on
March 2nd.  Additional outlooks may be issued if conditions change
significantly.  Long range probabilistic outlooks are issued near
the end of the month throughout the year under this same product
name and heading.

...Additional Information...

Visit our web site at weather.gov/pueblo for more hydrologic
information including graphs of probabilistic river outlooks.
You can link to the hydrology page by clicking on Rivers and
Lakes near the top of the page.

$$

LW



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