Extended Streamflow Guidance
Issued by NWS West Gulf RFC

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ESGFWR

SPRING FLOOD OUTLOOK
NATIONAL WEATHER SERVICE
WEST GULF RIVER FORECAST CENTER, FORT WORTH, TX
1 PM CST WED MARCH 1, 2017

The spring flood potential for the West Gulf River Forecast Center
drainage area covering portions of southern Colorado, New Mexico,
and Texas that flows into the Gulf of Mexico, is near to slightly above average
based upon current antecedent conditions.  For the southern Rocky
Mountains, which includes the San Juans and Sangre de Cristos, that
drain into the upper Rio Grande and Pecos river basins, spring flooding
driven by snowmelt runoff is not expected, despite the current above average
snowpack conditions.

This outlook considers antecedent rainfall, snowpack, soil moisture,
current streamflow, and watersupply conditions compared to climatology
combined with longer-term 90-day climate outlook forecasts for
temperatures and precipitation across the forecast area.

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
areas in the northwest portions of the WGRFC forecast area can be
affected by snowmelt occurring from as early as mid-March through
April timeframe.  These mountainous areas of southern Colorado and
northern New Mexico can accumulate a significant winter snowpack.
The most significant factors for spring flooding in mountainous
terrain are amount of water in the snowpack and the timing of the melt,
which could be combined with periods of heavy rainfall runoff.
However, normal weather regimes producing rapid snowmelt and/or
heavy rain-on-snow events, statistically have a low probability of
occurrence in this area even during El Nino driven weather patterns.


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


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

The information below reflects conditions through the end of February.
Conditions across the area have shown an improvement compared to
the same period last year.  Near to well-above average snowpack is currently
observed and likewise for watersupply forecasts within the southern Colorado
and northern New Mexico mountains.  However, the 90 day climate outlook
indicate a trend toward drier, warmer conditions which may accelerate
meltout this season with earlier than normal peak flows and could reduce
watersupply forecasts later in the season.

Regionally, snowpack SWE conditions within the upper Rio Grande and
Pecos in Colorado and New Mexico are tracking above to well-above average.
However, in general, leeward side SWE conditions are less than the windward
side of the San Juans, which will ultimately effect runoff within the upper
Rio Grande headwaters into the mainstem.

These snowpack conditions were supported with a regular pattern very strong
storm systems from mid-December thru Janaury despite relatively dry conditions
to start the season and near average conditions thru February, which ended with
another strong storm system adding another foot of snowpack over the past
three days.  Precipitation received for the water-year-to-date is above normal
even with the exception of the dry early season start and below normal February
precipitation.  For areas near Albuquerque and south
to Elephant Butte Reservoir, precipitation has been well above average
as winter storms favored western, central and points south of Albuquerque.
Much of the precipitation has fallen as rain rather than snow at lower
elevations this year.

Current observed basin streamflows along the mainstem and tributaries
without ice impairment are near or below normal.  Reservoir conditions
are below normal in New Mexico. The Elephant Butte reservoir is 15% of
storage capacity down from 18% a year ago.

Historically, mountainous snowpack, particularly in the higher
elevations, increases into April with additional storms, but recent
trends indicate the timing of peak accumulations and melt-out are
occurring 2 up to 6 weeks earlier.  However, any enhanced
precipitation and cooler temperatures through March can help provide
protection despite possible dust-on-snow and wind events that can
greatly reduce the snowpack, although climate outlooks are predicting warmer
and drier than normal conditions for March thru May.

Based on current snowpack conditions, near to above average streamflow is expected
this spring and throughout the seasonal runoff period.  However, the potential for
significant flooding from springtime snowmelt in the upper Rio Grande and Pecos
River basins remains low for the mainstem and associated tributaries, although
localized, minor diurnal flooding could be possible.

The Climate Prediction Center extended 90-day climate outlooks indicate greater
chances for above normal temperatures and below average precipitation.

The U.S. Drought Monitor has no drought conditions currently designated
for the upper Rio Grande and Pecos basins in Colorado and New Mexico,
which is considerable improvement from the moderate to severe
conditions a year ago.  And the U.S. Seasonal Drought Outlook
indicates no expected development of drought conditions across these
areas in the next 90 days.

WGRFC/Cazier


...West and south Texas generally west of Wichita Falls to San
   Antonio to Brownsville line, including portions of the upper
   Brazos, upper Colorado, upper Guadalupe, Nueces, San Antonio
   and lower Rio Grande basins

The potential for significant spring flooding over these basin areas
in Texas is near average at this time.

In the past 60 days, most of these basins have received near average
rainfall ranging from 75 to 125 percent of normal.  Current basin
streamflows are near average seasonal baseflow based on the latest
USGS Streamflow Index.  Reservoir storage in the region is also normal
to high with the exception of the upper Colorado which is listed as
severely low.  The  U.S. Drought Monitor indicates no current drought
conditions due in part to timely widespread rainfalls during the past
90 days.  Some short-term abnormally dry conditions exist in parts of
northeast Texas, the Texas panhandle and deep south Texas including much
of the lower Rio Grande River basin.

The U.S. Seasonal Drought Outlook for the next 90 days indicates short-term
drought persistence in northeast Texas near the Red River and over deep
south Texas. Extended 90-day climate outlooks indicate a 33 to nearly 50
percent chance of below average precipitation over west Texas, with equal
chances of below, near or above normal rainfall over central and east Texas.
There is a greater than 50 percent chance of above average temperatures.
The potential for spring flooding is expected to be near or slightly below
average over the next 90 days.


...The eastern portions of Texas including the Neches, Sabine,
   Trinity, lower Brazos, lower Colorado, lower Guadalupe, and
   San Jacinto river basins.

Potential for spring flooding in this area is near to above average at this
time with higher potentials across the southeastern Texas basins, the lower
Brazos and along the rivers along an near the middle and upper Texas Gulf Coast.

Most of the basins in this region have received near to above average rainfall
for this time of year, with above normal rainfall experienced along the
Gulf Coast to the area below Toledo Bend Lake.  Streamflow conditions across
this region are near to slightly above normal. Recent rain events have lead
to increased soil moisture content over southeastern Texas, primarily in the
lower Brazos, Lavaca/Navidad and San Bernard river basins.  Most area reservoirs
are near conservation levels ranging from 95 percent or more of conservation
storage percent capacity.

The U.S. Drought Outlook indicates no additional drought development is expected
over eastern Texas.  Elevated soil moisture over basins in eastern and
southeastern Texas may result in substantial runoff from any heavy spring rains
over this area.  Extended 90-day climate outlooks call for equal chances below,
near or above average precipitation with a greater than 50 percent chance of above
average temperatures. Typically, river flooding is increasingly probable during
the spring months in this region, where convective storms can quickly produce
rapid runoff causing flash-flood and mainstem flood conditions.  Slow vegetation
growth combined with the possibility of near normal precipitation could enhance
the potential for spring flooding across in this region.

WGRFC/Story

...Texas statewide reservoir conditions

At the end of February, total storage in 114 of the states major
water supply reservoirs was 87% of total conservation storage
capacity. There is no sigbificant change in storage from this time
last year.  Percent Full is based on Conservation Storage and
Conservation Capacity and doesn`t account for storage in flood pool.

More details are available under the Reservoir Summaries listed in
the References and Links section shown below.

WGRFC/Cazier
---------------------------------------

REFERENCES/LINKS:

Precipitation Analysis:
http://water.weather.gov/precip/
http://www.hprcc.unl.edu/maps.php?map=ACISClimateMaps

Snowpack Conditions:
http://www.wcc.nrcs.usda.gov/reports/SelectUpdateReport.html
http://www.wcc.nrcs.usda.gov/ftpref/gis/images/west_swepctnormal_update.png
http://www.wcc.nrcs.usda.gov/ftpref/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

WGRFC

$$



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