Flood Potential Outlook
Issued by NWS Denver/Boulder, CO

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FGUS75 KBOU 022010
ESFBOU
COC001-005-013-014-019-031-035-039-047-049-057-059-069-073-075-087-
093-095-115-117-121-123-031200-

Probabilistic Hydrologic Outlook
National Weather Service Denver/Boulder CO
110 PM MST Thu Mar 2 2017

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

This outlook is for north central and northeast Colorado and
includes the Colorado...North Platte and South Platte Rivers.

.Flood Outlook Highlights...
* Near average risk of minor snowmelt flooding in the North and
  South Platte River basins.
* Slightly above average risk of minor snowmelt flooding in the
  headwaters of the Colorado River in north central Colorado.
  Areas prone to flooding in the past may experience issues again
  this year.
* Significant flooding due to mountain snow runoff alone is not
  likely. However...it is still early in the snow accumulation
  season and conditions could change before the runoff begins.

Flooding from snowmelt typically occurs in May and early June. The
flood potential is very dependent on weather conditions from now
until the melt. The amount of additional snow and rain and the
timing of peak flows will have a significant effect on whether it
floods.

The potential for rain-induced flash flooding is not quantifiable
because this type of flooding is usually caused by localized
thunderstorms during the spring and summer.

.Current Hydrologic Conditions...
Mountain snowpack remains in good condition...ranging from 123
percent of normal in the North Platte basin to 131 percent of normal
in the Colorado River basin. Even though mountain snowpack does not
typically peak until April...March 1st snowpack was already 92...99
and 108 percent of the normal peak snowpack in the South
Platte...North Platte and Colorado River basins...respectively. It
is generally drier east of the Continental Divide below 7000 to 7500
foot elevations.

75 percent of the U.S. Geological Survey stream gages with a long
historical record had normal flows on March 1st.

Soil moisture is near normal west of the Continental Divide. Farther
east the soils are drier. Soil moisture continues to show deficits
across the eastern plains and evaporative demand on the plains show
a lot of stress in that region.

There is very little snow on the Colorado Plains. Although
meteorological winter (December through February) is typically the
driest season of the year for the Front Range Urban Corridor and
Colorado Plains...short-term dryness continues to be a concern east
of the Continental Divide.

Severe Drought /D2/ in western Lincoln County was expanded into
southern and central Lincoln County on the east central plains in
late February. Moderate Drought /D1/ and Abnormally Dry conditions
/D0/ continue elsewhere east of the divide. There were no drought
designations immediately west of the divide on the latest U.S.
Drought Monitor.

.Climate Summary...
Precipitation and temperatures have generally been near to above
normal the past 90 days. Temperatures were 4 to 10 degrees above
normal for February. February was drier than either December or
January. Precipitation totals for February are listed below:

Location           County     2017  Normal Departure % Normal
--------           ------     ----  ------ --------- --------
North Central Mountains/Foothills
 Conifer 6NE       Jefferson  0.46    0.90    -0.44      51
 Georgetown        Clear Ck   0.60    0.85    -0.25      71
 Georgetown 4SW    Clear Ck   1.00    0.89     0.11     112
 Virginia Dale7ENE Larimer    0.76    0.50     0.26     152
 Williams Fork Res Grand      1.04    0.86     0.18     121
 Winter Park       Grand      2.09    2.15    -0.06      97

Front Range Urban Corridor
 Boulder           Boulder    0.73    0.82     -0.09     89
 Castle Rock       Douglas    0.12    0.65     -0.53     18
 Denver area       Denver     0.23    0.37     -0.14     62
 Fort Collins      Larimer    0.52    0.40      0.12    130
 Loveland 2N       Larimer    0.46    0.52     -0.06     88
 Wheat Ridge       Jefferson  0.13    0.70     -0.57     19

Northeast/East Central Colorado Plains
 Akron 4E          Washington 0.16    0.40     -0.24     40
 Holyoke           Phillips   0.30    0.49     -0.19     61
 Leroy 5WSW        Logan      0.44    0.41      0.03    107
 New Raymer 21N    Weld       0.28    0.36     -0.08     78
 Sedgwick 5S       Sedgwick   0.32    0.53     -0.21     60
 Woodrow 6NNE      Morgan     0.09    0.34     -0.25     26

Unofficial NWS Cooperative Observer precipitation totals for
December through February (meteorological winter) are shown below:

Location       Elevation 2016-2017 Normal  Departure  % Normal
--------       ---------   -----   ------  ---------  --------
North Central Mountains/Foothills
 Conifer 6NE        7180    1.82    2.66    -0.84        68
 Georgetown         8520    4.62    2.44     2.18       189
 Georgetown 4SW    10020    6.59    2.62     3.97       252
 Virginia Dale 7ENE 7015    2.34    1.48     0.86       158
 Williams Fork Rsvr 7618    4.11    2.57     1.54       160
 Winter Park        9108    9.44    6.50     2.94       145

Front Range Urban Corridor
 Boulder            6484    3.05    2.52      0.53      121
 Castle Rock        6184    1.44    2.01     -0.57       72
 Denver area        5284    1.55    1.13      0.42      137
 Fort Collins       5004    1.93    1.30      0.63      148
 Loveland 2N        5080    2.09    1.64      0.45      127
 Wheat Ridge        5398    1.84    2.17     -0.33       85

Northeast/East Central Colorado Plains
 Akron 4E           4540    1.03    1.18     -0.15       87
 Holyoke            3780    1.10    1.35     -0.25       81
 Leroy 5WSW         4550    1.19    1.16      0.03      103
 New Raymer 21N     5180    1.64    1.05      0.59      156
 Sedgwick 5S        3990    1.18    1.35     -0.17       87
 Woodrow 6NNE       4374    1.22    1.11      0.11      110

.Weather Outlooks...
The outlooks for the month of March indicate a higher likelihood of
above normal temperatures and below normal precipitation.

.Numerical River Outlooks...
In Table 1 below, the current (CS) and historical (HS) or normal
probabilities of exceeding minor...moderate...and major flood stage
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 greater 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: 3/4/2017 - 6/2/2017

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:South Platte River
South Platte         7.0    9.0   11.0 :  <5   <5   <5   <5   <5   <5
Denver              11.0   12.5   14.0 :  <5   <5   <5   <5   <5   <5
Henderson           10.0   11.0   15.0 :   5    6   <5   <5   <5   <5
Kersey              10.0   11.5   13.0 :   8    9    5    6   <5   <5
Weldona             10.0   11.0   13.0 :   7    8    5    6   <5   <5
Balzac              10.0   11.0   13.0 :   8    8    5    6   <5   <5
Julesburg           10.0   11.0   12.0 :   5    6   <5   <5   <5   <5
:Plum Creek
Sedalia              8.0   10.0   12.0 :  <5   <5   <5   <5   <5   <5
:Bear Creek
Morrison             9.0   10.0   11.0 :  <5   <5   <5   <5   <5   <5
Sheridan             8.0   10.0   11.0 :  <5   <5   <5   <5   <5   <5
:Clear Creek
Golden              10.0   13.0   14.0 :  <5   <5   <5   <5   <5   <5
Derby                9.0   10.5   11.5 :  <5   <5   <5   <5   <5   <5
:N Fk Big Thompson River
Drake                6.0    7.0    8.0 :  <5   <5   <5   <5   <5   <5
:Cache la Poudre River
Fort Collins 9NW     7.5    9.0   10.5 :  <5   <5   <5   <5   <5   <5
Fort Collins        10.5   11.5   13.0 :  <5   <5   <5   <5   <5   <5
Greeley              8.0    9.5   10.5 :   7   <5   <5   <5   <5   <5
:North Platte River
Northgate            8.0    9.5   11.0 :   6   <5   <5   <5   <5   <5

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

In Table 2 below...the 95 through 5 percent columns indicate the
probability of exceeding the listed stage levels (FT) for the valid
time period.

Table 2--Exceedance Probabilities

                              Chance of Exceeding Stages
                                 at Specific Locations
                           Valid Period: 3/4/2017 - 6/2/2017
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:South Platte River
South Platte          3.8    3.8    3.9    4.0    4.3    4.8    5.2
Denver                4.1    4.2    4.5    5.1    5.6    6.5    7.1
Henderson             5.5    5.7    6.1    6.9    8.0    9.0   10.1
Kersey                4.4    4.8    5.2    6.6    8.6    9.5   11.6
Weldona               3.1    3.3    3.8    4.9    7.2    8.4   11.0
Balzac                2.6    3.0    3.4    4.9    7.2    8.5   11.0
Julesburg             4.6    4.8    5.4    6.6    7.6    8.4    9.9
:Plum Creek
Sedalia               4.1    4.1    4.2    4.4    4.8    5.4    6.9
:Bear Creek
Morrison              6.1    6.2    6.4    6.5    6.8    7.2    7.7
Sheridan              2.7    2.7    3.0    3.2    3.9    4.5    4.8
:Clear Creek
Golden                4.6    4.7    5.0    5.3    5.4    5.8    6.1
Derby                 2.5    2.7    2.9    3.2    3.7    4.4    5.0
:N Fk Big Thompson River
Drake                 4.0    4.1    4.2    4.3    4.4    4.6    4.9
:Cache la Poudre River
Fort Collins 9NW      4.0    4.2    4.3    4.6    5.0    5.6    7.1
Fort Collins          2.4    2.6    3.1    3.5    4.1    5.7    7.8
Greeley               2.7    2.8    3.5    4.8    6.0    7.5    8.4
:North Platte River
Northgate             5.0    5.2    5.3    5.9    6.7    7.4    8.1

In Table 3 below...the 95 through 5 percent columns indicate the
probability of falling below the listed stage levels (FT) for
the valid time period.

Table 3--Nonexceedance Probabilities

                            Chance of Falling Below Stages
                                 at Specific Locations
                           Valid Period: 3/4/2017 - 6/2/2017
LOCATION              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:South Platte River
South Platte          2.8    2.8    2.8    2.8    2.8    2.8    2.8
Denver                3.1    3.1    3.1    3.1    3.0    3.0    3.0
Henderson             4.1    3.8    3.3    3.1    3.0    3.0    3.0
Kersey                3.6    3.3    3.0    2.8    2.7    2.6    2.6
Weldona               2.1    1.6    1.0    0.3    0.1    0.1    0.1
Balzac                1.9    1.8    1.8    1.8    1.8    1.8    1.8
Julesburg             1.8    1.8    1.8    1.8    1.8    1.8    1.8
:Plum Creek
Sedalia               3.8    3.7    3.7    3.7    3.6    3.6    3.6
:Bear Creek
Morrison              5.5    5.5    5.5    5.5    5.5    5.5    5.4
Sheridan              2.3    2.2    2.1    2.1    2.1    2.1    2.1
:Clear Creek
Golden                3.5    3.5    3.5    3.5    3.5    3.5    3.5
Derby                 1.0    1.0    1.0    1.0    1.0    1.0    1.0
:N Fk Big Thompson River
Drake                 3.8    3.8    3.8    3.8    3.8    3.7    3.7
:Cache la Poudre River
Fort Collins 9NW      2.8    2.8    2.8    2.8    2.8    2.8    2.8
Fort Collins          1.2    1.2    1.2    0.7    0.4    0.4    0.4
Greeley               1.8    1.3    1.3    1.3    1.3    1.3    1.3
:North Platte River
Northgate             2.4    2.4    2.4    2.4    2.4    2.4    2.4

These long-range probabilistic outlooks contain forecast values that
are calculated using multiple season scenarios from 30 or more 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 a range of
probabilities...the level of risk associated with long-range
planning decisions can be determined. These probabilistic forecasts
are part of the National Weather Service`s Advanced Hydrologic
Prediction Service.

Visit our web site weather.gov/bou for more weather and water
information.

This will be the last flood and water resources outlook for the
spring 2017 season. Long-range probabilistic outlooks are issued
toward the end of each month throughout the year.

$$
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