Flood Potential Outlook
Issued by NWS Hastings, NE

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Probabilistic Hydrologic Outlook
National Weather Service Hastings NE
131 PM CST Thu Mar 07 2019

...Spring Flood and Water Resources Outlook Number 2...

This outlook is for the Hastings Hydrologic Service Area (HSA). In
South Central Nebraska this outlook includes the
Platte...Loup...Little Blue...and Republican Rivers and their
tributaries. In North Central Kansas...the Solomon River and its
tributaries are included.

...The potential for spring flooding is above average across the
majority of the area...

...Short Term Hydrologic Outlook...March 7th - March 31st...

In the short term through Monday March 11th we expect very little if
any snowmelt with high temperatures that at best will only be around
or a little above the freezing mark. We expect two additional storm
systems to bring more precipitation to the region within the next
week between March 7th and March 14th. The first system Friday night
into Saturday March 9th could add a little moisture primarily in the
form of rain that will likely just add to the moisture content
within the snow cover rather than melt much of the snow. Therefore,
flooding due to snow melt or rainfall runoff is not very likely
through Monday March 11th. However, we still will need to be mindful
of ice jam flooding along the the Platte River, which is already on
going near the Interstate 80 Grand Island exit. This ice jam
flooding is unlikely to change much over the next week due to the
continued cold temperatures.

The second storm system should impact the region Tuesday March 12th
and Wednesday March 13th. This could potentially be a stronger
system with some forecast models indicating over 1 inch of liquid
equivalent precipitation. The track of this storm system is still
very uncertain and will make a big difference on precipitation type
and amounts. There is certainly a flooding concern if we do end up
receiving over 1 inch rainfall amounts on top of our deep snowpack,
which would quickly melt our snow and result in significant runoff
given our deeply frozen ground. However, If we end up on the cold
side of the Tuesday-Wednesday system and get snow again, the
flooding concerns will only be delayed until the snow melts. If the
snow melts slowly enough, this could help to greatly minimize the
flooding threat and thus much attention will then turn towards how
quickly we warm up at the end of March.

There are multiple reasons for flooding concerns as we head through
March. The pattern has been cold and active allowing for snow to
pile up with liquid equivalent amounts of 1 to 2 inches within the
snowpack across much of our forecast area. In addition, the frost
depth as of March 7th was around 2 feet across portions of south
central Nebraska, which is the most significant frost depth we have
seen at any point in the winter for at least the last 5 years. A
frozen ground will allow for greater runoff and with an active
precipitation pattern likely to continue this leads to enhanced
flooding concerns, with the potential storm system March 12-13 being
of particular concern. Furthermore, most of our rivers remain
covered by a thick sheet of ice from our late winter cold spell.
This thick ice will increase our threat for ice jams primarily on
the Loup and Platte River which are more prone to ice jams.


...Long Term Hydrologic Outlook...April Through June 7th...

The potential for spring flooding is above average across the
majority of the area.

Spring flood outlooks are routinely issued from February through
March to give advanced notice of possible flooding. They are based
on soil moisture, snowpack magnitude, stream flow conditions, and
the long range forecast of future precipitation patterns.

There are several primary factors leading to our above average
threat for spring flooding.
- We had a very wet fall and early winter with especially December
being exceptionally moist. This moisture quickly froze and became
locked in within our soil through the winter. Consequently, soil
moisture readings are currently among the wettest on record in the
95th to 99th percentile where 100 percent would be considered the
wettest on record.
- The long range climate outlook through June is calling for better
than normal chances for above normal spring precipitation across our
hydrologic service area.
- Mountain snowpack that feeds the Platte River Basin is 100 to 120
percent of normal. Therefore, we expect at least average to a little
above average mountain runoff that will increase the chance for
elevated spring flows down the Platte River.
- Current stream flows have been ranging from near normal to much
above normal across the hydrologic service area.

Therefore, after considering all of the above mentioned factors, the
overall forecast for a majority of our hydrologic service area is to
expect an above normal chance of spring flooding and abnormally high
river levels. Even though the chance of spring flooding is above
normal, it is by no means a guarantee. The antecedent conditions are
in place for an increased flood risk this spring, but if heavier
than normal rains fails to materialize, then flooding (if any) would
likely be minimal.


...Climatological Review (Winter 2018-19 and recent precipitation
trends)...

In the previous issuance of this statement back on Feb. 21, this
section contained precipitation details for the previous year of
2018 across the 30-county NWS Hastings coverage area (24 counties in
Nebraska and 6 in Kansas). Please refer to that statement for
annual 2018 precipitation information.

From this point forward, the focus will be on more recent
precipitation trends over the past three months, specifically what
transpired during "meteorological winter" of 2018-19, which just
ended last week on Feb. 28 (meteorological winter consists of the
three full calendar months of Dec-Jan-Feb).

As evidenced in the data presented in the table below (and supported
by NWS AHPS precipitation analysis), this meteorological winter
featured MUCH ABOVE NORMAL precipitation, with most of our 30-county
area somewhere between two and three times normal! In fact, places
such as Holdrege, Hebron and Beloit recorded their wettest-on-record
Dec-Feb period! The primary contributor to this extremely wet winter
was December, which was among the top-3 wettest on record in most
places, thanks mainly to two unusually-heavy (for winter) rain
events.

Winter drought trends:
According to weekly updates by the U.S. Drought Monitor, our entire
30-county area has remained solidly drought-free so far this winter,
given the much-wetter than normal conditions. Keeping things in
perspective though, one must keep in mind that no matter how much
precipitation falls during the winter, it usually only accounts for
a small percentage of total annual precipitation, the vast majority
of which falls during the spring and summer.

The next table below highlights precipitation totals and departures
from normal/percent of normal for meteorological winter, covering
Dec. 1 - Feb. 28. Data is shown for just a small sampling of
official NWS cooperative observers, along with a few primary airport
sites. (For full access to daily/monthly/annual precipitation totals
in our area, please visit the NOWData page:
https://w2.weather.gov/climate/xmacis.php?wfo=gid)

  Location          Precip                            Percent of
North Central KS  Dec 1-Feb 28    Normal   Departure    Normal
--------           --------       ------   ---------  --------
Beloit               5.83          2.47      +3.36       236
Burr Oak             5.10          2.11      +2.99       225
Plainville 4WNW      4.47          2.10      +2.37       213
Smith Center         4.44          1.73      +2.71       257


  Location          Precip                            Percent of
South Central NE  Dec 1-Feb 28    Normal   Departure     Normal
--------           --------       ------   ---------  --------
Grand Island Arpt    4.39          1.84      +2.55       239
Hastings Airport     3.88          1.51      +2.37       257
Hebron               6.04          2.44      +3.60       248
Holdrege             5.63          1.65      +3.98       341
Kearney Airport      4.74          1.61      +3.13       294
Ord                  4.50          1.81      +2.69       249
York 3N              5.44          2.91      +2.53       187



...Weather/Climatological Outlook For The Next Week Through The Next
Three Months...

It`s now time to switch gears and look ahead to expected weather
conditions over the next several days and expected climate trends
over the next several months:

Starting with the most immediate local weather expectations over the
next week (through March 14): According to the latest NWS Hastings 7-
day forecast, the upcoming week looks to feature a continued active
weather pattern, with the potential for two fairly significant
precipitation systems, one focused on Saturday and the next perhaps
during the Monday night-Wednesday time frame. One or both of these
systems could drop appreciable rain and/or snow within parts of the
local area. Temperature-wise, most of the area just endured the 2nd-
coldest opening week of March on record, and although the severity
of the recent cold looks to moderate during the next week, there
remains a high likelihood that temperatures will continue to average
below normal through at least mid-March.

March outlook (one-month): Now that most of the local area has
already endured the 2nd-coldest opening week of March on record,
it`s already a good possibility that the month as a whole will end
up colder than normal. The latest one-month outlook from the Climate
Prediction Center (CPC) updated on Feb. 28 clearly favors below
normal temperatures for the month as a whole (60-70 percent chance).
Precipitation-wise, the month is at least slithly favored for above
normal precipitation, which makes sense given recent and upcoming
precipitation potential. As a point of reference, normal March
precipitation across the local area ranges from around 1.40" in the
western-most counties (such as Dawson/Furnas), up to around 2.10" in
far eastern counties along and near Highway 81 (such as
York/Thayer). Temperature-wise, long-term 30-year normals (based on
1981-2010 data) indicate that March high temperatures across South
Central Nebraska and North Central Kansas gradually climb from
averages in the mid-40s/near-50 early in the month to the upper
50s/low 60s by month`s end. Average daily low temperatures gradually
increase from around 20 to around 30 degrees.

3-Month Outlook for March-May: Turning to the meteorological spring
months of March-April-May as a whole, the latest three-month outlook
valid for March-May (released Feb. 21) shows no truly strong climate
signals regarding temperatures, with "equal chances" assigned region-
wide. For spring precipitation, roughly the northeast half of the
area is assigned equal chances, while the southwest half very
slightly favors above normal precipitation (33-40 percent chance).
Again, "equal chances" means that long range forecast tools just do
not present enough of a signal to support one of these possible
outcomes over another. Although there are no truly strong signals
regarding upcoming spring precipitation trends, one can keep in mind
that 30-year normal precipitation from March-May across the NWS
Hastings coverage area typically ranges from 7-10 inches, with the
lowest amounts generally west of Highway 183 and highest amounts
near the Highway 81 corridor.

U.S. Seasonal Drought Outlook (issued by CPC on Feb. 21 and valid
through the end of May):
This outlook indicates that there are no strong indications to
suggest drought conditions will develop. This not only pertains to
our local area south central Nebraska and north central Kansas, but
across the entire Central Plains region.

(The longer range forecasts issued by CPC and referenced in the
preceding paragraphs are based on output from various forecast
models, as well as forecaster expertise, and take into consideration
ongoing global/tropical atmospheric and oceanic states, recent
trends in observed data, soil moisture conditions, etc. More
information about these longer-range forecasts can be obtained from
the CPC web site at: https://www.cpc.ncep.noaa.gov)


...Long Range Probabilistic Outlooks...

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 Period:  03/09/2019  - 06/07/2019

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Little Blue River
Deweese             10.0   16.0   17.0 :  89   31   26   <5   18   <5
:North Fork Solomon
Glade               11.0   16.0   18.0 :  48   10   15   <5    6   <5
:Bow Creek
Stockton             9.0   12.0   13.6 :  66   17   18   <5   <5   <5
:Platte River
Cozad                7.5    9.0   11.0 :  32   23    9    7   <5   <5
Overton              7.5   12.0   14.0 :  14   15   <5   <5   <5   <5
Kearney              7.0    8.0    9.0 :  17   15   11    8    9    5
Grand Island         6.5    7.0    7.5 :  58   18   39   15   28    9
:Wood River
Gibbon              15.0   16.0   16.5 : >98   31  >98   17   93   16
Alda                10.0   11.0   12.2 : >98   36  >98   32  >98   16
:South Loup River
Ravenna              5.0    8.0   10.0 :  80   36   40    9   17    5
:Mud Creek
Sweetwater          16.5   18.0   21.0 :  39   23   23    6    5   <5
:South Loup River
Saint Michael        7.5   12.0   15.0 :  57   25    5   <5   <5   <5
:Middle Loup River
Saint Paul           8.0   10.0   12.0 :  16   <5   <5   <5   <5   <5
:North Loup River
Saint Paul           7.0   10.0   12.0 :  29   <5   <5   <5   <5   <5
:Cedar River
Fullerton            9.0   17.0   18.0 :  39    5   <5   <5   <5   <5
:Loup River
Genoa               10.5   12.0   13.0 :  62   14   41    7   31   <5
:Beaver Creek
Genoa               15.0   17.0   19.0 :  71   15   48    6   30   <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: 03/09/2019  - 06/07/2019
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Little Blue River
Deweese               8.9    9.8   10.7   13.2   16.2   19.8   23.2
:North Fork Solomon
Glade                 5.7    6.5    7.4   10.7   13.3   16.8   18.4
:Bow Creek
Stockton              6.6    6.8    8.1    9.9   11.0   12.9   13.1
:Platte River
Cozad                 3.3    3.5    4.9    6.2    7.7    8.9    9.7
Overton               3.9    3.9    4.4    5.3    6.5    8.8   10.7
Kearney               3.3    3.6    4.3    5.1    6.2    8.5    9.7
Grand Island          5.2    5.3    5.7    6.7    7.6    9.1    9.5
:Wood River
Gibbon               16.4   16.5   17.0   17.8   18.2   18.9   19.3
Alda                 12.3   12.4   12.7   13.1   13.3   13.5   13.9
:South Loup River
Ravenna               4.2    4.3    5.2    6.0    9.2   10.9   11.7
:Mud Creek
Sweetwater           10.3   10.6   12.0   14.3   17.8   19.4   21.1
:South Loup River
Saint Michael         4.8    4.9    6.2    8.0   10.1   11.3   12.0
:Middle Loup River
Saint Paul            3.6    3.7    4.6    5.3    6.8    8.4    8.7
:North Loup River
Saint Paul            4.2    4.4    4.8    6.0    7.1    8.5    9.0
:Cedar River
Fullerton             5.0    5.2    5.8    7.7   10.7   13.0   14.4
:Loup River
Genoa                 8.5    8.7    9.7   11.1   13.5   15.3   16.1
:Beaver Creek
Genoa                11.9   12.8   14.6   16.7   19.4   21.6   22.2

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: 03/09/2019  - 06/07/2019
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Little Blue River
Deweese               2.4    2.4    2.4    2.4    2.4    2.2    2.2
:North Fork Solomon
Glade                 3.0    3.0    3.0    2.9    2.7    2.5    2.3
:Bow Creek
Stockton              4.2    4.2    4.2    4.2    4.2    4.1    4.1
:Platte River
Cozad                 3.2    2.5    2.4    2.3    2.2    2.2    2.2
Overton               3.5    3.4    3.1    2.8    2.7    2.7    2.7
Kearney               3.1    2.8    2.2    1.8    1.2    0.8    0.8
Grand Island          4.1    4.0    3.7    3.4    3.2    3.2    3.2
:Wood River
Gibbon                4.1    4.1    4.1    4.1    4.1    4.1    4.1
Alda                  4.5    4.4    4.4    4.4    4.4    4.4    4.4
:South Loup River
Ravenna               2.8    2.8    2.8    2.8    2.8    2.7    2.7
:Mud Creek
Sweetwater            5.8    5.8    5.8    5.8    5.6    5.5    5.3
:South Loup River
Saint Michael         2.6    2.6    2.6    2.6    2.5    2.4    2.4
:Middle Loup River
Saint Paul            2.1    2.1    2.1    1.9    1.6    1.5    1.5
:North Loup River
Saint Paul            3.0    3.0    3.0    3.0    2.9    2.8    2.7
:Cedar River
Fullerton             3.1    3.1    3.1    3.1    3.1    3.1    3.0
:Loup River
Genoa                 4.6    4.6    4.6    4.6    4.6    4.6    4.6
:Beaver Creek
Genoa                 3.5    3.5    3.5    3.5    3.5    3.4    3.4

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.


...Future Outlooks...

This is the second and final spring flood outlook. The next
probabilistic hydrologic outlook will be issued on or around April
23rd.

&&

Visit our local NWS office website for current weather/hydrological
and climate information for South Central Nebraska and North Central
Kansas at:
https://www.weather.gov/hastings

Additional climate information for the region can be obtained
from the High Plains Regional Climate Center: https://hprcc.unl.edu

Additional information on climatological outlooks can be found
from the Climate Prediction Center: https://www.cpc.ncep.noaa.gov

Further information on drought conditions can be obtained at:
https://www.drought.gov
https://www.drought.unl.edu
https://droughtmonitor.unl.edu

Information on mountain snowpack can be found at:
https://www.wcc.nrcs.usda.gov

NWS AHPS precipitation analysis maps can be found at:
https://water.weather.gov/precip

National snow analysis page can be found at:
https://www.nohrsc.noaa.gov

Soil Moisture:
https://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring

Reservoir Levels:
www.usbr.gov/gp/hydromet/curres_google.htm

For training on NWS river forecast graphics:
www.youtube.com/watch?v=psIByj8EZY0

$$

Wesely/Pfannkuch





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