Miriam Needed Rain, Flooding Risk for Texas

By , Expert Senior Meteorologist
September 26, 2012; 4:50 AM ET
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Drenching rain will reach grazing areas and perhaps some winter wheat growing areas of the South-Central states. Photos.com image.

Tropical rainfall, due in part to Miriam, will bring benefits and flooding concerns to portions of Texas Friday into the weekend.

Some tropical moisture on the eastern side of Miriam in the Eastern Pacific will merge with Gulf of Mexico moisture over Texas and northern Mexico before the end of the week.

According to Western Weather Expert Ken Clark, "The circulation from Miriam will diminish near Baja California, Mexico and the heaviest rain will be squeezed out along the west coast of Mexico and the nearby mountains."

Any drenching, non-flooding rainfall would benefit agricultural areas and hydrological concerns. A large part of the U.S. Southwest and Plains states, as well as northern Mexico continue to suffer from drought conditions.

"The circulation around Miriam and a southerly flow ahead of front over the southern Plains will work to bring rain to large tracts in Texas," Clark stated.

At this point it appears the bulk of the rain will slide up over central and eastern Texas, more so than western Texas and New Mexico.

There is the potential for 2 to 4 inches of rain to fall from west-central and the Big Bend areas to the coast, with locally higher amounts over a 48- to 72-hour period.

Miriam, a tropical storm in the Eastern Pacific, as of early Wednesday morning, Sept. 26, 2012, will slowly weaken later this week.

Miriam strengthened on Monday, but began weakening early Tuesday morning. The latest information on intensity and forecast track of Miriam can be found on AccuWeather.com's Hurricane Center. Tropical moisture will still be ejected northeastward, even if Miriam completely breaks up.

"A swath pocket of dry air will remain parked over much of California, Nevada and Arizona and will keep the rain away from these areas," Clark added.

Based on the latest information, AccuWeather.com meteorologists expect rain, in part associated with Miriam, part with the Gulf of Mexico, to fall Thursday night into Saturday over a large part of Texas and a portion of Oklahoma.

According to AccuWeather.com's Agricultural Weather Expert Dale Mohler, "September is prime planting time for the winter wheat."

The extent and amount of rain contributed by Miriam's moisture and another, weaker system during the middle of the week is questionable and certainly will not reach everywhere.

The system over the Rockies during Monday will spread spotty rainfall mainly across eastern Colorado, Kansas, Missouri and parts of Oklahoma through the middle of the week. Some of this rainfall could fall over a short period of time, in the form of thunderstorm downpours.

"Any non-flooding rain from Miriam, the Gulf or a front would be a great boost for soil moisture at this time of planting and germination for the winter wheat." Mohler said.

The rain would also help green up pastures in Texas and the Southwest.

Tropical moisture from Miriam and the Gulf would come into play farther south late in the week.

While people in Texas and northern Mexico will generally welcome the rain they should also be on alert for the risk of rapid flooding.

There have not been many Eastern Pacific tropical cyclones that brought drenching rain to the Southwest, relative to the number of systems that affected Mexico or steered away from the West coast.

Systems that have delivered locally heavy rainfall and flooding in the Southwest in recent decades include Javier in 2004, Nora in 1997, Lester in 1992, Raymond in 1989, Kathleen in 1976 and interestingly Katrina in 1967.

Winter wheat is essentially a grass. The plant needs a certain amount of moisture to germinate and establish a root system. Germination, depending on soil and weather conditions, averages five to 10 days.

The ground in some areas of the southern Plains became bone dry and dusty following the intense summer heat and drought of 2012.

During the winter, the wheat goes dormant, only to re-sprout vigorously in the spring, provided harsh freezes without the protection of snow cover did not occur.

This past winter, although snow was lacking over the Plains, temperatures remained well above average and there were no severe freezes.

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