Flood Potential Outlook
Issued by NWS Albuquerque, NM

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Probabilistic Hydrologic Outlook
National Weather Service Albuquerque NM
1055 AM MST Thu Mar 7 2019

...NORMAL FLOOD RISK FOR NORTHERN AND CENTRAL NEW MEXICO...

...NORMAL BUT INCREASING FLOOD RISK FOR THE ANIMAS RIVER...

...ISOLATED AREAS OF ABOVE NORMAL FLOOD RISK FOR SMALLER TRIBUARIES
IN THE RIO CHAMA AND RIO GRANDE BASINS...


...EXISTING CONDITIONS...

The main story of the 2018-2019 Water Year has been one of El Nino,
drought, and drought recovery. As expected, weak El Nino conditions
developed in the equatorial Pacific Ocean, which has generally been
beneficial in the recovery from the dry and damaging 2017-2018 Water
Year.

The last 36 months in the region have been a hydrometeorlogical
rollercoaster with conditions ranging between two extremes. The 2016-
2017 Water Year was very beneficial for New Mexico with above normal
snowpack values during the winter and a robust monsoon season. This
surplus allowed for the recharge of soil moisture conditions
throughout most of the region and an increase in reservoir storage
from previous seasons. As La Nina developed, precipitation came to a
halt in mid-October 2017. As the 2017-2018 Water Year progressed,
record low snowpack over the region led to near record low runoff
volumes. Coupled with above normal temperatures, the lack of
precipitation and high evapotranspiration rates helped to deplete
soil moisture values statewide. The 2018 Monsoon Season helped to
bring needed moisture back to much of New Mexico, but the Four
Corners region as well as much of the Northern Mountains missed the
needed rainfall. The 2018-2019 Water Year began with beneficial
moisture, but a drying period from November through late December
began to negate any gains from October. Starting in late December, a
continuous stream of storm systems have helped to bring snowpack
values in the Northern Mountains up to normal to above normal. This
constant stream of systems has begun to improve drought conditions
over much of the Land of Enchantment.

Not all areas of northern and central New Mexico have seen the
sustained precipitation totals, however with areas in the west-
central part of the state as well as the lee of the Central Mountain
Chain seeing below normal precipitation totals and above normal
evapotranspiration rates over the last 30-60 days.

El Nino is expected to begin to diminish through the Spring, however
the impacts in the short term are expected to continue with a
generally active weather pattern expected through the remainder of
March. Above normal mountain snowpack in the Northern Mountains is
expected to lead to generally normal runoff volumes.


...PRECIPITATION...

With severe to exceptional drought gripping a large part of New
Mexico through the 2017-2018 Water Year, a wet October 2018 was a
welcome start to the new water year. The late season burst of
rainfall (and early season snow) helped to alleviate drought
conditions over much of central and northern New Mexico. Monthly
precipitation departures for much of the Pecos River, lower Canadian
River, and the central and southern Rio Grande Valley were over 200%
of normal for the month. Precipitation was less fruitful in other
areas with continued dry conditions persisting in the Four Corners,
upper Rio Grande Valley, and portions of the Sacramento Mountains.
The wet trend did not continue into November and into the third week
of December as a dry pattern established itself over the region with
much of New Mexico receiving less than 50% of normal precipitation.

Over the last 90 days, the precipitation trend for most of the
Southwest and Rockies has been wet due an increase in the frequency
of storm systems moving through the region. Precipitation began to
increase over many areas in the last week of December as the pattern
became more active. However, several areas remain below normal in
the 90-day period including areas in the lee of the Central Mountain
Chain as well as portions of west-central New Mexico.

In the shorter 30-45 day period, high elevations in northern New
Mexico have continued to see above normal precipitation as well as a
noted increase in precipitation in the San Juan River valley in
northwest New Mexico. However, the drying trend is continuing over
many areas east of the Central Mountain Chain and the Southwestern
Mountains.

...SNOWPACK...

In a typical year, mountain areas in New Mexico tend to see the
majority of their precipitation during the winter in the form of
snow. While the 2017-2018 winter was one of the lowest on record
with respect to snowfall, conditions in the 2018-2019 season have
steadily improved as El Nino conditions have settled over the
Southwest. Winter 2018-2019 was off to a snow start with some early
season systems in October 2018, but through November and most of
December 2018 winter precipitation was largely limited to the Sangre
de Cristo mountains. Starting with the last week of December 2018, a
steady flow of weather systems quickly brought basins in northern
New Mexico and Colorado to normal or above normal. This trend has
been maintained through the winter.

Conditions in southern New Mexico basins have not been as productive
as those seen in northern New Mexico. Several weather systems early
in the season produced normal snow totals, however as winter
progressed the trend became for generally warmer systems, thus
producing mainly rainfall rather than snow.

In Colorado, the headwaters of the Rio Grande, San Juan, and Animas
basins are around 130% of normal. In New Mexico, northern New Mexico
basins are near to above normal with the Rio Chama the highest at
119% of normal. Southern New Mexico basins are all below normal with
the San Francisco basin the highest at 72%. The Rio Hondo and
Mimbres basins have generally melted out as of this date.

Climatologically, basins in southern New Mexico tend to see their
peak SWE values by early-March while basins further north reach
their climatological peak later in March or the first half of April.

...RESERVOIR SUMMARY...

Due to the well below normal runoff and precipitation in the 2017-
2018 Water Year, overall reservoir conditions throughout the state
are below normal for early March. Reservoirs on the Rio Grande
system are overall well below normal with Cochiti Reservoir being
the only large reservoir with a storage over 50% (79% on March 1).
Elephant Butte is the lowest on the Rio Grande system with a March
1st storage of 13%. Navajo Dam (67%) on the San Juan River and
Conchas Dam (64%) on the Canadian River are in better shape than
many of the Rio Grande, but still below normal. Due to late season
rainfall and management practices, the main reservoirs on the Pecos
River are near normal. All reservoirs in New Mexico have adequate
flood storage space.

Of note, long-term averages for reservoirs use data from the
19812010 period. During this time, reservoirs along the Rio Grande
had higher storage values due to a wetter period that influenced the
first half of the 30-year period. Therefore, the 30-year average is
statistically skewed to a higher value and may not be reflective of
reservoir storage trends for the previous 15 years.

...STREAMFLOW CONDITIONS AND RUNOFF FORECASTS...

Streamflow conditions over northern and central New Mexico are
reflective of both the dry 2017-2018 Water Year as well as the
recent hydrometeorological trends. Natural flowing basins in the
western one-third of New Mexico have mostly experienced below-normal
streamflow conditions due to the below normal precipitation over the
last 15-18 months, but recent storm systems have improved conditions
to near normal. Streamflow trends over the Rio Grande basin are
generally dominated by the very dry conditions and poor runoff in
2018, but tributaries are beginning to see the influence of the
recent wet conditions. Over eastern New Mexico, conditions vary as
some locations in the Canadian River basin are still seeing the
impact of the drought. Increased streamflow is apparent along
portions of the upper Pecos and the Rio Hondo as recent moist
conditions and early melt out on the Rio Hondo are bringing
streamflows above normal.

NWS River Forecast Centers, in conjunction with our partners in the
NRCS, USACE, and the USBR, produce seasonal streamflow forecasts for
selected river locations and basins in New Mexico. These forecasts
are based on hydrologic conditions as of the first of the month and
may not reflect current trends and forecasts.

Seasonal runoff forecasts in New Mexico vary considerably. Runoff
forecasts for the San Juan, Rio Grande, and Pecos River basins are
generally in the normal range. Below normal runoff values are
expected in the Canadian River basin as well as all basins in
southern New Mexico.

These outlooks are based on the available SWE within the river
basins and climatologically expected conditions at runoff.
Departures from climatological conditions at runoff (such as heavy
rainfall or a loss of SWE before the normal melt out time) may
change seasonal runoff volumes. Another factor that may impact
seasonal runoff volumes will be depleted soil moisture values in the
deeper layers of the top soil due to the extended drought. Current
trends in precipitation are likely to balance this out for many
rivers, but regions where both the SWE values and recent
precipitation values are below normal may see a reduced seasonal
volume.

...DROUGHT...

Drought conditions over New Mexico have generally continued to
improve over the last 60-90 days as El Nino influenced storm systems
have continued to produce normal to above normal precipitation
conditions for much of the state. A large portion of northern New
Mexico remains in D3 or Extreme Drought due to the longer term
precipitation deficits dating back to October 2017. Impacts in these
areas have been enhanced due to above normal evapotranspiration
rates over much of 2018, which in turn increased environmental
demand for moisture and greatly depleted soil moisture in the deeper
layers of the soil column. D4, or exceptional drought, remains in
portions of San Juan County where the 15-18 month deficits have been
the largest.

Drying conditions have been observed in portions of southeastern and
eastern New Mexico where there has been a trend the last 30-60
towards warmer and dryer conditions. Conditions will monitored for
any potential redevelopment of drought conditions.

The drought status for New Mexico is re-evaluated weekly and can be
found at the National Drought Mitigation Center website at
http://droughtmonitor.unl.edu.

...CLIMATE OUTLOOK...

The NWS/Climate Prediction Center anticipates that El Nino
conditions will continue through early Spring 2019 and will begin to
return to an ENSO-Neutral condition by late Spring 2019. Climate
outlooks for March through May are reflective of the expected
impacts of diminishing El Nino.

The temperature outlook for March through May for almost of New
Mexico as well as the Southern Rockies indicates that equal chances
of above, normal, or below normal temperatures are exist.
Precipitation outlooks are typical of a waning El Nino with normal
to above normal precipitation likely.

These outlooks are issued monthly with the next outlook to be issued
on March 21th. Outlooks can be found at the NWS/CPC website at
http://www.cpc.ncep.noaa.gov.

...SPRING FLOOD OUTLOOK...

Taking into consideration of all current hydrometeorological
factors, most basins in northern and central New Mexico have a
normal risk of spring flooding.

Spring flooding related to snowmelt is uncommon on larger rivers in
New Mexico, especially after the construction of the larger dams on
the mainstem rivers. The primary factors in this assessment are the
normal to above normal SWE values, below normal deep-layer soil
moisture values, and current hydrometeorological trends.

The Canadian, San Francisco, Rio Hondo, and Gila Basins typically do
not see flooding due to spring runoff and normally experiences
flooding related to heavy rainfall or mid-winter rain-on-snow
events, thus a normal flood risk is expected.

Some tributary basins in the Rio Chama and western slopes of the
Sangre de Cristo Mountains may have an above normal risk of spring
flooding due the increasing snowpack in those regions. Current
trends in precipitation and conditions at runoff will have to need
be monitored in those basins.

While currently listed as a normal flood risk, conditions in for the
Animas River basin will have to be monitored closely. The SWE values
in the San Juan Mountains of Colorado are already at the median
value for a normal season with almost month left until the normal
climatological peak of the season. If current trends continue or
conditions at runoff are above normal (i.e. heavy rain and/or warm
temperatures), the risk of flooding on the Animas River may increase.

The NWS Albuquerque Hydrologic Service Area (HSA) is serviced by
three River Forecast Centers: West Gulf RFC (Fort Worth, TX),
Arkansas-Red Basin RFC (Tulsa, OK), and the Colorado River Basin RFC
(Salt Lake City, UT). These RFCs issue a variety of hydrologic
forecast products during the year. Further products and current
information can be found at the following locations:

https://www.weather.gov/wgrfc https://www.weather.gov/abrfc
https://www.cbrfc.noaa.gov

You can also find additional weather and water products and
forecasts at the NWS Albuquerque website at:

https://www.weather.gov/abq

For questions or comments about this outlook, you can contact Royce
Fontenot, Senior Service Hydrologist, at 505-244-9150 x 228 or via e-
mail at royce.fontenot@noaa.gov.

$$

54/Fontenot



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