Flood Potential Outlook
Issued by NWS Midland/Odessa, TX

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122359-
SPRING FLOOD OUTLOOK
NATIONAL WEATHER SERVICE MIDLAND/ODESSA TX
600 PM CST THU MAR 5, 2015

The spring flood potential for the Midland/Odessa National Weather
Service drainage area covering portions of Southeast New Mexico and
West Texas is below average based upon current antecedent
conditions.  For the southern Rocky Mountains, which includes the
San Juans and Sangre de Cristos, snowmelt runoff draining into the
upper Rio Grande and Pecos river basins to produce spring flooding
is unlikely and not expected based on the current snowpack
conditions.

This outlook considers antecedent rainfall, snowpack, soil moisture,
streamflow, and water supply conditions compared to climatology
combined with longer-term 90-day forecasts for temperatures and
precipitation across the forecast area.  The most significant factors
for spring flooding are amount of water in the snowpack and the
timing of the melt.

The primary factor in development of significant river flooding over
most of the region is the occurrence of excessive rainfall in
relatively short periods of time, even for areas where drought
conditions persist or have developed.  In addition, the mountainous
area in the northwest portion of the  forecast area can be affected
by rapid snowmelt, usually occurring in the spring months.  These
mountainous areas of southern Colorado and northern New Mexico can
receive significant winter snowpack accumulation.  However, normal
weather regimes producing rapid snowmelt and/or heavy rain on snow
events, statistically these have a low probability of occurrence in
this area.  Above average snowpack is currently not observed or
forecast within the southern Colorado and northern New Mexico
mountains.

The general outlook for specific basin areas in the region follow:


...Upper Rio Grande and Pecos basin, Colorado and New Mexico

The current general basin wide snow conditions within the upper Rio
Grande in Colorado and New Mexico are still generally tracking below
average, but improving with a regular pattern of storm systems over
the past few week. In contrast, the Pecos River basin received some
unusually heavy rainfall amounts last fall along with additional
snow/rain events boosting the precipitation totals over the basin to
values ranging from 150 to 400-plus percent above average over the
past 60 days.

Recent storms have also dropped much needed snow over the mountainous
regions throughout south central Colorado and northern New Mexico,
increasing seasonal forecast streamflows, but still generally below
normal; the exception being near normal streamflow forecasts along
the middle/upper Sangres.  However, the potential for spring flooding
remains low.

Looking at snowpack, the range varies widely, however, the upper Rio
Grande basin in Colorado is generally 65 to 90 percent of normal for
snow water equivalent basin-wide with localized above and below
outliers.  Across New Mexico in the Rio Grande and Pecos basins, snow
water equivalents range from 60 to near 90 percent of normal.  Along
the northern and middle Sangres in Colorado and New Mexico, the
snowpack improves with a general range from 90 to 110-plus percent.

Historically, mountainous snowpack, particularly in the higher
elevations, increases into April with additional storms.  The timing
on storms in the region is tracking near normal but the magnitude
continues to be genrally below normal amounts.  As a result, peak
snowpacks are expected to continue below normal levels with melt
likely occurring earlier than normal this season. However, any
enhanced precipitation and cooler temperatures through March would
provide protection despite the typical dust-on-snow and wind events
that greatly reduce the snowpack. Based on current snowpack
conditions, below average streamflow is expected this spring and
throughout the seasonal runoff period.  The potential for significant
flooding from springtime snowmelt in the upper Rio Grande and Pecos
River basins remains significantly reduced for the mainstem and
associated tributaries.  Current basin streamflows along the mainstem
and tributaries are below normal in Colorado and New Mexico, as well
as, reservoir storage.

The U.S. Drought Monitor indicates abnormally dry to moderate drought
conditions for the upper Rio Grande basin in Colorado and New Mexico
extending to severe drought conditions across the upper Pecos basin.
The 90 day U.S. Seasonal Drought Outlook indicates persistence or
slight improvement of drought conditions in the entire Rio Grande
basin in Colorado and New Mexico.

Extended 90-day climate outlooks indicate equal chances of above,
below, or near normal temperatures and a 40 percent chance of above
average precipitation. These conditions may result in mitigating
early snowmelt.  Overall, the potential for spring time flooding as
a result of snowmelt runoff is very low.

...The upper Colorado basin of West Texas

The potential for significant spring flooding over this basin area
in Texas is below average at this time.

In the past 60 days, this basin has received near average rainfall
ranging from 75 to 125 percent of normal.  Current basin streamflows
are generally below seasonal baseflow.  Reservoir storage in the
region is also very low ranging from nearly empty to 39 percent of
conservation.  The  U.S. Drought Monitor indicates improvement in
drought conditions across most of western Texas.

The U.S. Seasonal drought outlook for the next 90 days indicates
drought persistence likely across the basin.  Extended 90-day
climate outlooks indicate a 33 to 40 percent chance of above average
precipitation and 33 to 40 percent chance of below average
temperature.  The potential for spring flooding remains well below
average at this time.

REFERENCES/LINKS:

Precipitation Analysis:
http://water.weather.gov/precip/

Snowpack Conditions:
http://www.wcc.nrcs.usda.gov/reports/SelectUpdateReport.html
ftp://ftp.wcc.nrcs.usda.gov/data/water/wcs/gis/maps/
west_swepctnormal_update.pdf
ftp://ftp.wcc.nrcs.usda.gov/data/water/wcs/gis/maps/WestwideSWEPercent
.pdf

Streamflow Conditions:
http://waterdata.usgs.gov/nwis/rt
http://www.dwr.state.co.us/Surfacewater/default.aspx

Reservoir Summaries:
http://www.wcc.nrcs.usda.gov/basin.html
http://www.waterdatafortexas.org/reservoirs/statewide

Soil Moisture Conditions:
http://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/US/Soilmst/
Soilmst.shtml

Us Drought Monitor And Outlook:
http://droughtmonitor.unl.edu/
http://www.cpc.noaa.gov/products/expert_assessment/season_drought.png

Tx Drought Information:
http://waterdatafortexas.org/drought/

Climate Graphics:
http://www.cpc.noaa.gov/
http://www.cpc.noaa.gov/products/predictions/long_range/lead01/
off01_temp.gif
http://www.cpc.noaa.gov/products/predictions/long_range/lead01/
off01_prcp.gif

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