Flood Potential Outlook
Issued by NWS Pueblo, CO

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PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE PUEBLO CO
1005 AM MST THU February 15 2018

...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.

This Outlook is valid from February 14 TO May 15, 2018.

The Potential for Spring flooding, caused by snowmelt alone, is
below normal in the Arkansas River basin.

The Potential for Spring flooding, caused by snowmelt alone, is
below normal in the Rio Grande basin.

...OUTLOOK FOR THE ARKANSAS BASIN...

It has been very dry and relatively warm since the beginning of the
water year (October 1, 2017). This has limited the accumulation of
snowpack throughout the area. The potential for spring flooding due
to snowmelt during the next 90 days is extremely limited and below
normal.

Any snowmelt flooding that develops will most likely be minor and
would only result in minimal property damage and minor public threat
or inconvenience.

Table 1. below, shows the Current (CS) and Historical (HS) or normal
probabilities of exceeding minor, moderate, and major flood stages.
The values are valid for the time period from February 14 to May 15.

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 Period:  02/14/2018 - 05/15/2018

                                       :    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
Leadville            9.0   10.0   12.0 :  <5   <5   <5   <5   <5   <5
Salida               8.0    9.0   10.0 :  <5   <5   <5   <5   <5   <5
Wellsville           9.0   10.0   11.0 :  <5   <5   <5   <5   <5   <5
Parkdale             9.0   10.0   11.0 :  <5   <5   <5   <5   <5   <5
Canon City          10.0   12.0   14.0 :  <5   <5   <5   <5   <5   <5
Portland             9.0   10.0   11.0 :  <5   <5   <5   <5   <5   <5
Pueblo               8.0    9.0   11.0 :  <5   <5   <5   <5   <5   <5
Avondale             7.0    8.0    9.0 :   5   <5   <5   <5   <5   <5
Nepesta             16.5   17.5   18.5 :  <5   <5   <5   <5   <5   <5
Fowler               8.0    9.0   10.0 :  <5   <5   <5   <5   <5   <5
Rocky Ford          10.0   11.0   12.0 :  <5   <5   <5   <5   <5   <5
La Junta            11.0   13.0   15.0 :   8   10   <5   <5   <5   <5
Lamar               11.0   13.0   15.0 :  <5   <5   <5   <5   <5   <5

:Fountain Creek
Colorado Springs    11.5   16.0   18.0 :  <5   <5   <5   <5   <5   <5
Fountain            12.0   14.0   16.0 :  <5   <5   <5   <5   <5   <5
Pinon               12.0   14.0   15.0 :  <5   <5   <5   <5   <5   <5
Pueblo              10.0   12.0   13.5 :  <5   <5   <5   <5   <5   <5

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

:Purgatoire River
Madrid               7.0    9.0   11.0 :  <5   <5   <5   <5   <5   <5
Trinidad Lake       10.0   12.0   14.0 :  <5   <5   <5   <5   <5   <5
Trinidad            11.0   12.0   13.0 :  <5   <5   <5   <5   <5   <5
Las Animas           9.0   12.0   15.0 :  13    8   <5   <5   <5   <5

Legend
CS = Conditional Simulation (Current Outlook)
HS = Historical Simulation
FT = Feet

It can be seen in the table above that the chance of exceeding flood
stage is very low in a normal year. This analysis is for the period
ending May 15 and our normal snowmelt period is from late May to mid-
June. The below-normal runoff would be observed in that normal
snowmelt period. These results are consistent with a very low
snowpack expected to melt in late May or early June.

Any snowmelt flooding that develops will most likely be minor and
would result in minimal property damage or threat to the public and
only minor inconveniences.

Snowmelt flooding should not be confused with other types of
flooding such as those associated with heavy rain from storms,
releases from reservoirs, or extreme runoff from burn scars. This
outlook does not address the potential for those types of floods.
Flooding and flash flooding from heavy rainfall or burn scar runoff
is always a possibility.

...OUTLOOK FOR THE RIO GRANDE BASIN...

The flood potential in the Rio Grande basin, from snowmelt runoff
alone, is below normal. Any snowmelt flooding that develops will
most likely be minor and would only result in minimal property
damage and minor public threat or inconvenience.

Probabilities of exceeding flood stage or various flood categories
such as those presented for the Arkansas basin are not currently
available for the Rio Grande basin. However, a qualitative
assessment of the flood potential in the Rio Grande basin is
provided below.

Snowpack in the Rio Grande basin is running about 43 percent of
median as of February 13. Reservoir storage at the end of January
was at 123 percent of average. Soil moisture is generally near
normal with values between the 30th-70th percentiles. Streams in the
area are either ice-covered or at low flow which is reflective of
normal conditions. The dry fall and extremely limited snowpack lead
to the conclusion that the probability of flooding in the next 90
days, due to snowmelt flooding alone is below normal.

Any snowmelt flooding that develops will most likely be minor and
would result in minimal property damage or threat to the public and
only minor inconveniences.

Snowmelt flooding should not be confused with other types of
flooding such as those associated with heavy rain from storms,
releases from reservoirs, or extreme runoff from burn scars. This
outlook does not address the potential for those types of floods.
Flooding and flash flooding from heavy rainfall or burn scar runoff
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 weather
conditions develop over the region during the next 3 months or
during the snowmelt period, then much more severe flooding could
occur.

...SUMMARY OF PAST...PRESENT AND FUTURE CONDITIONS...

Temperatures have been consistently above normal at climate stations
across southeast and south-central Colorado. Since, October 1,
monthly average temperatures at all 7 climate stations in the region
have been from 2-6 degrees above average.

Snowpack levels in the mountains of the Arkansas River and Rio
Grande basins are well below the median values for this time of
year. As of February 14, the snowpack in the mountains was 63
percent of normal in the Arkansas River basin and 43 percent of
median in the Rio Grande basin.

Precipitation for the Water Year (starting October 1, 2017) as
measured at NRCS SNOTEL stations in the mountains, is well-below
average in the Arkansas and Rio Grande basins. As of February 14,
the water year precipitation was 64 percent of average in the
Arkansas River basin and 43 percent of average in the Rio Grande.

As of February 1, overall reservoir storage is running about 121
percent of average in the Arkansas basin above Pueblo Reservoir.
Below Pueblo Reservoir the overall storage is running about 153
percent of normal. Storage in the Rio Grande basin is also robust at
123 percent of average.

Streamflow in the Arkansas basin is currently near to above normal.
This reflects the wet spring and summer of 2017. Streamflows remain
high despite the dry autumn. This has helped get the reservoir
storage to its elevated condition.  In the Rio Grande basin, streams
are either ice-covered or flowing near normal levels. This also
reflects the abundant moisture of last spring and fall.

Soil moisture for the plains is generally low at this time of year
and that holds true this year as well. Some areas in the mountains
are experiencing unusually dry soils.

...SCHEDULE OF OUTLOOKS...

This is the first of 2 scheduled Spring Flood and Water Resources
Outlooks for 2018. Additional outlooks may be issued if conditions
change significantly. Long range probabilistic outlooks for the
Arkansas River basin are issued near the second and fourth Thursdays
of most months. The next probabilistic outlook will be issued
February 22.

...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 the light blue
Rivers and Lakes tab near the top of the page.

$$

AJA



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