Flood Potential Outlook
Issued by NWS Albuquerque, NM

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Probabilistic Hydrologic Outlook
National Weather Service Albuquerque NM
1150 AM MDT Mon Mar 15 2021

...BELOW NORMAL FLOOD RISK FOR ALL OF NORTHERN AND CENTRAL NEW MEXICO...

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

...EXISTING CONDITIONS...

The 2020-2021 Water Year has been one dominated by ongoing
extreme to exceptional drought across much of New Mexico that took
hold during the fall of 2020 and into the winter. Winter season
precipitation has been a mix of above normal precipitation within
broader areas of below normal precipitation which has led to no
drought relief. Soil moisture has been depleted in much of the
extreme to exceptional drought areas especially across eastern New
Mexico. Snow water equivalent from winter snowfall are all below
normal for the water year, especially so for the Pecos River, Rio
Hondo, Mimbres and San Francisco Rivers.

...PRECIPITATION...

Below normal precipitation resulted across New Mexico as the La
Nina weather pattern became established across much of the United
States during the fall months of 2020 to start the 2020-2021 Water
Year. Most notable was southeast New Mexico and pockets of
northeast Highlands, eastern Plains and Gila Forest where there
has been less than 25 percent of normal precipitation for the
water year so far. There have been individual precipitation events
that yielded beneficial moisture to New Mexico such as those on
October 25-28, 2020, November 7-11, 2020 and December 8-12, 2020.
Unfortunately, these events did not provide enough widespread
precipitation to even ease drought conditions and 2020 ended with
more areas having long periods (14-21 days) of no measurable
precipitation.

2021 has not started any better than the end of 2020 but there
have been a few more precipitation events such as January 20-27,
2021 and February 11-18, 2021 that provided New Mexico with much
needed moisture. Soil moisture has increased in some areas such as
the Sangre de Cristo Mountains, but the areas that need it most
like the eastern Plains of New Mexico are still very dry.
Surprisingly, western San Juan County has had above normal
precipitation in the last 60 days, but this has only resulted in
maintaining severe to extreme drought conditions. Looking out
through the Spring, we expect below normal precipitation for much
of New Mexico as the La Nina pattern continues. This will all
contribute to a below normal flood risk.

...SNOWPACK...

The accumulation of snowpack over the Southern Rockies and
southern New Mexico got a good start with the October 25-28, 2020
precipitation event. However, much of that snowpack melted through
the beginning of November. There was some recovery of snowpack
towards the end of November and the beginning of December
especially with the December 8-12 event. The basins that
benefited the most were the Rio Chama, Upper Rio Grande, Sangre
de Cristo, and San Juan River in Colorado. Still these basins are
below normal for snow water equivalent (SWE) so far for the winter
with 75 to 100 percent of the 1981-2010 normals. The lone
exception is the Upper Rio Grande Basin (102 percent of normal).
The other basins across New Mexico are anywhere from 35 to 65
percent of the 1981-2010 normals with the Rio Hondo Basin only
having 6 percent of normal.

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. As of February 25, 2021, SWE percent of normal values in
New Mexico are below:

Rio Chama River Basin           84%
Upper Rio Grande Basin         104%
Sangre de Cristo Basins         61%
Jemez River Basin               54%
San Francisco River Basin       30%
Gila River Basin                62%
Mimbres River Basin             16%
Pecos River Basin               43%
Cimarron River Basin            76%
Zuni/Bluewater Basin            53%
Rio Hondo Basin                  3%

In Colorado:

San Juan River Headwaters       83%
Animas River Basin              81%

...RESERVOIR SUMMARY...

Given the ongoing drought conditions, overall reservoir storage
is well below normal with all reservoirs below 1981-2010 averages.

Reservoirs on the Rio Grande system are overall below normal with
Cochiti Lake having the highest storage (71%) and El Vado/Heron
Reservoirs below 20% of average. The Caballo Reservoir is at 39%
of average just down from 44% a year ago, however Elephant Butte
is only at 12% of average compared to 44% of average a year ago.
On other river systems, storage varies but again well below normal
averages. Navajo Dam on the San Juan River is currently at 81% of
normal storage. Eagle Nest Reservoir on the Cimarron River is at
66%, while reservoirs on the Pecos River vary dramatically. Santa
Rosa Reservoir comes in at having only 7% of average while Lake
Sumner and Brantley Lake have 54% and 60% respectively.

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 the 2020 Monsoon season that yielded below normal
precipitation, ongoing drought conditions supported by the La Nina
weather pattern as well as the current hydrometeorological
conditions. This means below normal soil moisture levels continue,
allowing for any precipitation to soak into the ground with
little to no runoff into any of the watersheds or basins.

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 are generally below
normal. Runoff forecasts for the San Juan, Rio Grande, and the
Gila/San Francisco basins are in the below normal range. This is
primarily due to below normal SWE values in combination with dry
soil moisture values that must be replenished first by the
snowmelt. Runoff forecasts are below normal for the Pecos River
and Canadian River Basins due to the below normal SWE values.

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 failure of the 2020
Monsoon Season much like 2019.

...DROUGHT...

Drought conditions at the start of the 2020-2021 Water Year
expanded over New Mexico and intensified in response to the below
normal monsoon as well as a dry early winter season due to the La
Nina weather pattern. Nearly 100 percent of the state is in severe
drought (D2) or worse. Roughly 54 percent of the state is
experiencing exceptional drought (D4), an increase of 51 percent
from the start of the Water Year. The ongoing La Nina weather
pattern should continue to support below normal precipitation
through the spring. This means extreme and exceptional drought
conditions could expand ahead of the 2021 monsoon season.

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 La Nina
conditions will continue through Spring 2021. There is a 60
percent chance of La Nina transitioning to an ENSO neutral phase
during the months of April, May and June of 2021. Based on these
trends and the latest climate modeling, we expect New Mexico to
have below normal precipitation and above normal temperatures
compared to the 1981-2010 averages for the Spring season. Above
normal temperatures may continue into the summer but equal chances
of below or above normal precipitation. Much above normal
precipitation during the summer months will be needed to ease
drought conditions.

These outlooks are issued monthly with the next outlook to be
issued on March 18th. Outlooks can be found at the NWS/CPC website
at http://www.cpc.ncep.noaa.gov.

...SPRING FLOOD OUTLOOK...

Considering all the hydrometeorological and drought factors,
basins in northern and central New Mexico have a below 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 below normal SWE values, below normal
deep-layer soil moisture values, and current hydrometeorological
trends.

While the Rio Grande can see high flows from snowmelt, flooding
is rare. The combination of low soil moisture and below normal SWE
give a below normal risk of flooding on the Rio Grande. The Pecos
River typically does not experience snowmelt flooding as well,
and a below normal risk of spring flooding is expected since SWE
values are below normal in the headwaters.

The Canadian, San Francisco, Rio Hondo, and Gila Basins typically
do not see flooding due to spring runoff and normally experience
flooding related to heavy rainfall or mid-winter rain-on-snow
events. Given ongoing drought and below normal SWE, a below normal
risk of flooding is expected.

Some smaller tributary basins in the Rio Chama and the Sangre de
Cristo Mountains may have a normal risk of spring flooding due
localized snowpack in those regions. While SWE is closer to normal
but still lacking, current trends in precipitation and conditions
at runoff will need to be monitored in those basins.

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
Scott Overpeck, Warning Coordination Meteorologist, at
505-244-9150 x 223 or via e- mail at scott.overpeck@noaa.gov.

$$


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