Flood Potential Outlook
Issued by NWS Pueblo, CO

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PROBABILISTIC HYDROLOGIC OUTLOOK NATIONAL WEATHER SERVICE PUEBLO CO
1100 AM MST THU March 1 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 March 1 TO May 28, 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...

February saw a strong accumulation of snowpack in both the Rio
Grande and Arkansas basins. However, the generous snows of February
have not been enough to offset the very dry and relatively warm
weather since the beginning of the water year (October 1, 2017).
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 March 1 to May 29.

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  02/27/2018 - 05/28/2018

                                    : 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    7   <5   <5   <5   <5
Portland          9.0   10.0   11.0    <5   <5   <5   <5   <5   <5
Pueblo Res.       8.0    9.0   11.0    <5   <5   <5   <5   <5   <5
Avondale          7.0    8.0    9.0    10    9    7    7   <5   <5
Nepesta          16.5   17.5   18.5     8   <5   <5   <5   <5   <5
Caitlin Dam       8.0    9.0   10.0     6    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    16   19   <5   <5   <5   <5
Lamar            11.0   13.0   15.0    <5    6   <5   <5   <5   <5

:Fountain Creek
Colorado Springs 13.0   16.0   18.0    <5   <5   <5   <5   <5   <5
Fountain          8.0   10.0   12.0    <5   <5   <5   <5   <5   <5
Pinon             7.0    9.0   10.0    <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 Dam     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    20    9   <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 28 and our normal snowmelt period is from late May to
mid-June. Those locations where the probability of reaching flood
stage is greater than 5 percent show no strong difference between
the current (CS) conditions and historical (HS) or normal
conditions. 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 59 percent of
median as of February 28. 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 in February were considerably closer to the average
that has been the case for most of the winter. Monthly average
temperatures from October through January, at all 7 climate stations
in the region have been from 2-6 degrees above average.

February brought robust snow accumulation to the upper Rio Grande
basin. Snowpack there rebounded considerably from the historic lows
seen through January. However, it did not overcome the water deficit
developed from October to January. 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 28, the
snowpack in the mountains was 65 percent of normal in the Arkansas
River basin and 59 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 28,
the water year precipitation was 67 percent of average in the
Arkansas River basin and 54 percent of average in the Rio Grande.

As of February 28, overall reservoir storage is running about 119
percent of average in the Arkansas basin above Pueblo Reservoir.
Below Pueblo Reservoir the overall storage is running about 175
percent of normal. Storage in the Rio Grande basin, as of February
1st was 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 second 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
March 8.

...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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