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Hydro-Meteorological Discussion

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315 AGUS74 KFWR 261739 HMDFWR HYDROMETEOROLOGICAL DISCUSSION NATIONAL WEATHER SERVICE...WEST GULF RFC...FORT WORTH TX 1139 AM CST THU NOV 26 2015 VALID NOVEMBER 26 THROUGH DECEMBER 1 ...RAINFALL IS DEVELOPING, WITH SIGNIFICANT RAINS EXPECTED OVER A GOOD PART OF THE REGION THIS AFTERNOON THROUGH SUNDAY.... ...METEOROLOGICAL DISCUSSION... A major storm system has formed to the west of the WGRFC area. At the surface, a moist southerly flow of Gulf moisture is occurring, with high level moisture also present from the eastern Pacific Ocean. As this moisture increased the past 24 hours, light showers developed over central and south Texas, as well as over parts of New Mexico and Colorado. Higher elevation snow can be expected today over the mountains of northern New Mexico and Colorado, and this snow should continue the next few days. A mixture of wintry precipitation is possible at lower elevations from eastern New Mexico through the Texas panhandle into western Oklahoma the next few days. More significant rainfall begins later today over most of Texas. A strong upper level low pressure system is located over northwestern Utah this morning. This low is forecast to remain steady or even shift westward through Saturday before moving northeastward to Wyoming on Monday of next week. Southwesterly flow has developed aloft over the WGRFC area of responsibility and will persist through the weekend. Due to the persistence of this flow a prolonged precipitation event is about to begin. At the surface, a strong cold front is expected to enter the western parts of North Texas today and then move slowly across the state on Friday. The cold front and upper level pattern will combine to produce conditions favorable for locally heavy rainfall over much of the WGRFC area, especially over north Texas, along an behind the front through Monday morning. In addition, the weather models are also forecasting that eastern Pacific Hurricane Sandra will move over southwestern Mexico as a Tropical Storm on Saturday before dissipating over land as it moves northeastward on Sunday. This system could cause some additional moisture to interact with the upper level storm system and cold front to enhance the heavy rainfall threat in Texas and western Louisiana through Sunday. In general, rainfall amounts of up to 8.00 inches are expected for areas along and north of I-20 from late today through Sunday, with the highest amounts near the Red River. Amounts of over 4.00 inches will be widespread across central and north Texas. We will continue to monitor the model guidance for any changes, and will update accordingly. Drier air from the west should shut down the prospects of significant rainfall on Monday into Tuesday morning as the upper low shifts eastward over Nebraska and Iowa. ...PRECIPITATION FORECAST... For Today into Friday morning, Mean Areal Precipitation (MAP) amounts of 0.25 to 1 inch are forecast for portions of southern Colorado, eastern and southern New Mexico, and the northwestern two thirds of Texas. The heaviest rain, with MAP amounts of 2 to 4 inches, are forecast for portions of North Texas especially along the Red River. MAP amounts of less than 0.25 inch are forecast for most of the rest of Texas and New Mexico. For Friday into Saturday morning, MAP amounts of 0.25 to 1 inch are forecast for most of southern Colorado into northern New Mexico, and from the southeastern third of New Mexico into most of the rest of Texas. The heaviest rain, with MAP amounts of 2 to 4 inches, are forecast from north central and northeastern Texas into eastern Oklahoma. MAP amounts of less than 0.25 inch are forecast for the rest of the WGRFC area. For Saturday into Sunday morning, MAP amounts of 0.25 to 0.50 inch are forecast for a good portion of Texas from the Big Bend through the Hill Country to northeast Texas. The heaviest rain, with MAP amounts of 1.50 to 2.00 inches, are forecast for most from central into northeastern Texas. MAP amounts of less than 0.25 inch are forecast for most of the rest of the WGRFC area. For Sunday into Tuesday morning, MAP amounts of 0.25 to 0.50 inch are forecast for central and east Texas into most of Louisiana. MAP amounts of less than 0.25 inch are forecast for most of the rest of Texas, northeast New Mexico and southern Colorado. Topsoil moisture has increased significantly with recent rainfall events which means it will require less rainfall for runoff to occur. That, along with the vegetation being dormant now that the growing season has come to an end, means runoff will be quicker. Over Texas only 7% of the state is abnormally dry, while over New Mexico, 26% of the state is abnormally dry. Heavy rainfall amounts of up to 8 inches are forecast over several days from late today through the weekend. This likely will lead to some potentially significant runoff because of the wet soil moisture and cold season vegetation patterns. ...HYDROLOGIC DISCUSSION... ...Trinity Basin... ...Minor Flooding... River stages continue to fall across the lower Trinity River. Minor flooding is still occurring downstream at Moss Bluff (MBFT2). ...Neches Basin... ...Minor Flooding... Minor flooding continues at various locations across the Neches River basin. River stages are falling. However, heavy rainfall is anticipated Friday through Saturday which may cause higher levels of flooding in the headwater basins. ...Sabine Basin... ...Minor Flooding... Toledo Bend Reservoir will continue generating power 24 hours per day until further notice at one unit of power generation. Additional heavy rainfall is expected Friday through Saturday which could cause significant flooding in the upper Sabine. ...Brazos Basin... ...Higher Flow Non-Flood Forecasts... Higher flows are occurring on the Navasota River and lower Brazos River. River stages have crested and continue receding. ...Remainder of WGRFC Basins... Additional heavy rainfall is expected Friday through Sunday that could cause another round of flooding in the headwaters of the Sabine, Neches and portions of the Trinity and Brazos. ...SUPPLEMENTARY GRAPHICAL INFORMATION... The following URLs (all lower case) provide additional graphical information on current and forecast hydrologic conditions, past and future precipitation, and drought and climate forecasts. This information is provided by a variety of National Weather Service, NOAA, and private sector entities. For specific information on river conditions, refer to the AHPS pages from the local NWS offices at: The Flood Potential Outlook can be viewed on our webpage at: The West Gulf River Forecast Center is now on Facebook: National Precipitation Analysis: The forecast rainfall amounts (QPF) can be viewed on our webpage at: The US Drought Assessment: The latest on Reservoir Information for Texas: STORY $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.