National Weather Service River Forecast Center

As we start the new year, I want to take a look back at some of the major accomplishments the LMRFC has made in 2004. We rose to the challenge with critical forecasts of major and record flooding during several periods this year. Spring flooding occurred over the LMRFC area and this was followed by a very active tropical season. The LMRFC area was largely spared the worst of the flooding from the tropical events but we still had some records broken in the French Broad River Basin due to heavy rainfall from Hurricane Francis. In addition to meeting operational requirements,the LMRFC implemented AHPS services at 27 locations in the Tennessee Valley and we were able to recalibrate our forecast model at over 20 locations to support this effort. Two LMRFC staff members received special recognition this year. Development and Operations

Hydrologist Bob Stucky received the prestigious Max Kohler Award for outstanding service to the people of the Lower Mississippi Valley. Senior Hydrologist Eric Jones was part of a group that received a NOAA Bronze Medal for implementing a backup computer system for RFCs. Congratulations to those two and congratulations to the entire LMRFC staff for their efforts and successes in 2004.

We expect a busy and successful year in 2005. We always like to hear from our customers about their needs. Please do not hesitate to call or email us and let us know how we are doing or if there are other services you need.

The Mississippi River is the longest and largest, in average annual water volume, of any river in North America, flowing 2,340 river miles from its source at Lake Itasca in the Minnesota North Woods to the Gulf of Mexico. The Mississippi Basin measures 1.84 million square miles, covering approximately 40% of the continental United States and covers about one-eighth of the North America Continent. Of the world’s largest rivers, the Mississippi ranks third in length, second in watershed area, and fifth in average annual discharge.

The Lower Mississippi River Forecast Center (LMRFC) is responsible for preparing and issuing river forecasts for 21 locations along the mainstems of the Ohio and Mississippi Rivers. Mainstem forecast products issued include daily 5-day forecasts, weekly 28-day forecasts, and seasonal spring flood outlooks. Preparation and issuance of these forecasts requires extensive coordination with upstream River Forecast Centers (RFC), the United States Army Corps of Engineers (USACE), the Tennessee Valley Authority (TVA), and six National Weather Service (NWS) Weather Forecast Offices (WFO).

Forecast Responsibility
The LMRFC mainstem responsibility begins on: 1) the Ohio River at Smithland Dam, IL, tailwater, 2) the Mississippi River below Chester, IL, 3) the Cumberland River below Barkley Dam, KY, 4) the Tennessee River below Kentucky Dam, KY, and 5) the Arkansas River below Pine Bluff, AR; and, includes all tributaries and drainage below these locations. This area covers the lower 62.1 river miles on the Ohio River, the lower 25.0 river miles on both the Cumberland and Tennessee Rivers, 1063.7 river miles on the Mississippi River, and the lower 40 miles on the Arkansas River.

Daily, 5-day stage forecasts are issued for 18 stations from Smithland Dam tailwater on the Ohio River to Cairo, IL, and on the Mississippi River from Cape Girardeau, MO, to New Orleans, LA. These forecasts are normally disseminated by 9:30AM in the NEWRVAORN product. Forecasts for three additional flood-only sites are included when stages are expected to reach flood stage or higher.

Each Wednesday, an extended 28-day forecast is issued for the Ohio River at Cairo and 15 locations on the Mississippi River in the NEWESPORN product. Seasonal Spring Flood Outlooks issued in the NEWESGORN product, are used to qualitatively discuss the potential for river flooding within the Mississippi Valley.

Forecasting Operations
The LMRFC uses the Dynamic Wave Operational (DWOPER) Model to simulate streamflow and stage for all forecast points along the Ohio and Mississippi Rivers. DWOPER is a one-dimensional, unsteady flow model which allows for simultaneous propagation of waves both upstream and downstream; providing solutions to complex backwater conditions. Forecaster skill is required to balance DWOPER output with well-known manual techniques and overall knowledge of the river system.

For simplicity, DWOPER is modeled as four mainstem Ohio/Mississippi segments: the Upper segment begins as described in the above section and ends at Memphis, TN; the Middle segment runs from Memphis to Vicksburg, MS; and the Lower from Vicksburg to the Gulf of Mexico. A stand-alone fourth segment runs from Red River Landing, LA, to West Pointe a la Hache, LA, and is used for forecasting hurricane surges as they propagate upstream along the lower reaches of the Mississippi (see Fig.1).

Figure 1

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The upstream DWOPER boundary conditions are the observed and forecasted streamflows at Smithland Lock and Dam, Chester, and at Kentucky and Barkley Dams Provided by the Ohio RFC (OHRFC) and North Central RFC (NCRFC) respectively. Observed discharges and projected releases for Barkley and Kentucky Dams are provided by the Tennessee Valley Authority (TVA).

Along the Middle and Lower Mississippi, other significant inflows/outflows include: 1) flows from the Arkansas-Red Basin RFC(ABRFC) for Pine Bluff, AR, on the Arkansas River, 2) Arkansas River discharges at Lock and Dam 2, AR, operated by the USACE Little Rock District (SWL), and 3) the Old River Outflow Control Structure near Simmesport, LA, operated by the USACE, New Orleans District (MVN). Throughout the Ohio/Mississippi complex, runoff from contributing mainstem local area basins and routed flows from smaller tributaries are computed using the NWS Sacramento Soil Moisture Accounting Model (SAC-SMA). The SAC-SMA computed flows are input as additional runoff and lateral inflows to the DWOPER system.

DWOPER output serves as a basis for forecasts on the Mississippi River. Empirical stage-to-stage relationships also provide valuable guidance to forecasted stages. Hydrologists forecasting the Mississippi River must utilize the strengths of DWOPER and the empirical manual techniques to prepare the best forecasts possible.

Coordination
During routine forecast operations, handoff of upstream data is automatically ingested to LMRFC models using local scripts and programs. The mainstem forecaster must closely coordinate the handoff of flows with the OHRFC, NCRFC, ABRFC, TVA, and six USACE Districts and two USACE Divisions. For cooperating agency planning purposes, a preliminary 7-day forecast for the Ohio River at both Cairo, IL, and Paducah, KY, are prepared around 830AM and issued to the USACE Great Lakes/Ohio River Division (LRD), USACE St. Louis District, and TVA. The forecaster must also closely coordinate the observed/predicted discharges from the Arkansas River at Dam 2 provided by the USACE SWL; and, the observed/predicted Mississippi River outflows from the Old River Control Structure provided by the USACE MVN.

However, forecasting the Mississippi River during observed or predicted flooding conditions requires a significant increase in the amount of inter/intra-agency coordination. When the Ohio River at Cairo rises above its 40 foot flood stage, the USACE LRD takes over regulation of Barkley and Kentucky Dams requiring close coordination with LRD and TVA. The LMRFC mainstem forecaster must also increase coordination with OHRFC and NCRFC forecasters on upstream handoff forecasts. In addition to LRD, close coordination with the USACE District Offices at Memphis, Vicksburg, and New Orleans is necessary for effective coordination of crest forecasts.

Figure 2

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Prior to release of official Ohio/Mississippi River forecasts, the mainstem forecaster must again coordinate with the LRD and reach a consensus on the 5-day forecast and projected crest at Cairo. If any changes to handoff flows or dam releases are received, a new DWOPER run is made and the coordination process with LRD is repeated. All upstream RFC boundary data is passed to LRD for use in their dynamic model. Following consensus, the official Ohio/Mississippi River forecast is released to the public.

During major flood events when the stage crest at Cairo is expected to reach or exceed 50 feet, the USACE begins detailed flood fight planning and invokes daily conference calls between the USACE Mississippi Valley Division, OHRFC, NCRFC, the Hydrometeorological Prediction Center in Camp Springs, MD, and the LMRFC. Other agencies requiring close coordination of changing river conditions are the Lower Ohio and Mississippi River Committee, a conglomerate of barge and towing companies; and, the US Coast Guard, the regulatory authority over all Mississippi River traffic.

The primary focus for close coordination of mainstem river and flood forecasting is to produce the best possible forecast for the benefit of the general public. Because mainstem forecasting has a direct impact on our Nation’s economy, close inter/intra-agency coordination is essential for producing the best possible set of NWS river and flood forecasts along the mainstems of the Ohio and Mississippi.