Thursday Weather Blog: Significant Rains Expected on Friday

By: Meteorologist Ray Hawthorne Email
By: Meteorologist Ray Hawthorne Email

The very active pattern that has brought plentiful winter rains will continue into the first week of meteorological spring.

Water vapor imagery is showing the beginnings of what will probably be a very wet end to the week. A deepening upper-level trough is moving southeastward from New Mexico into Texas this afternoon. There is also a vigorous jet streak spreading rapidly southward from the Canadian Prairies toward the Southwest U.S., which will contribute to the strengthening trough. This whole mess will gradually move eastward and be a big player in our weather on Friday and Friday night.

There is an area of more immediate concern, however. Increasing warm, moist advection -- and perhaps a weak impulse -- is causing showers and thunderstorms to develop in the Central and Eastern Gulf of Mexico. The crux of this moisture is headed more toward Central Florida, but some showers could scrape the far Southeastern Big Bend and the lower Suwannee River Valley just before sunset. This rain could spread into a large area of the Florida Big Bend coast, the Eastern Florida Big Bend and perhaps along/east of I-75 in South-Central Georgia during the nighttime hours. Other, more sporadic showers should gradually develop over the rest of the region overnight. Rainfall amounts from this first batch of rain will average between 0.25 and 0.75 inches (generally east of U.S. Highway 319), but localized spots might exceed an inch -- especially closer to I-75. Lighter amounts are expected along and northwest of a Thomasville-Tallahassee tonight.

The upper trough over Texas will then translate eastward into the Northwestern Gulf of Mexico this evening. Strong large-scale lifting within an increasingly warm/moist environment will cause an area of low pressure to form near the Texas/Louisiana coasts by midnight. Signals from many of the models are quite high that a line of very heavy showers and thunderstorms will organize along and ahead of this low pressure and move in from the west on Friday morning. Widespread rainfall totals of 2 to 5 inches are expected with this line as it criss-crosses the region. The GFS model is showing even more; in excess of 7 inches, but it's impossible to say where and even if those kinds of extreme amounts may occur at this time. There's also some indication that a weakly unstable airmass will spread inland from the Gulf in the presence of an intensely sheared environment. This would favor isolated supercells and perhaps bowing segments and LEWPs (line echo wave patterns) capable of producing damaging winds and an isolated tornado or two. The highest potential for this activity would be after 4 o'clock Friday morning.

Despite the threat of severe weather, we are most concerned about the flooding potential. The following rivers have the greatest potential to flood:

  • Ochlockonee River: renewed flows possibly up to moderate levels down the river into Lake Talquin will be possible

  • Aucilla River: the basin is at bank full levels and will be subject to significant rises (minor flooding)

  • St. Marks River: the basin is at bank full levels and will be subject to significant rises (minor to moderate flooding)

  • Sopchoppy River: the basin will be subject to significant rises

  • Okapilco Creek: the basin will be subject to significant rises

  • Upper Suwannee River Basin: the Withlachoochee, Alapaha, Little and Satilla Rivers are at bank full levels, and will be highly responsive to rainfall and rapid rises. Pinetta is not far below the 70 foot level which generated concerns recently and could easily rise above 70 feet fairly quickly after this rain event.

  • Middle and Suwannee River Basin: heavy rainfall over the Suwannee River could generate significantly higher flows next week. It would be prudent for interests of the Suwannee River to be prepared for significant rises over the next two weeks. Long-range projected crests of the Suwannee River will be available after this rain event.

  • Sante Fe River Basin: still relatively dry, however heavy rainfall could quickly increase flows downstream. The existing backwater rises from the Suwannee are projected to bring Three Rivers Estates to flood stage in 4 days. Three Rivers Estates could reach flood stage earlier than forecast if additional rainfall falls on the Sante Fe River Basin.

A special thanks to the National Weather Service for the above-mentioned river flood forecasts.

Everyone should monitor the weather situation carefully on Friday and have their Weather Radios tuned in for the latest severe weather information.

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  • by Derek Location: Tallahassee on Mar 7, 2008 at 07:51 PM
    Please tell your weather people or the powers that be that I really like these weather blogs. This was written a day before the storm hit and was right on target. I appreciate the detailed analysis. Thanks.
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