Flood Potential Outlook
Issued by NWS Huntsville, AL

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Hydrologic Outlook...Corrected
National Weather Service Huntsville AL
306 PM CST Thu Mar 1 2018

...Spring Flood Outlook for North Alabama and Southern Middle

The flood potential for the Tennessee Valley of Northern Alabama and
Southern Middle Tennessee favors above average flood potential for
Spring 2018. Though recent rainfall in November/December 2017 was
below normal, as was rainfall overall for January 2018, rainfall
really ramped up for the month of February, making up for lost time.
As a result from the heavy rainfall in February, soil moisture
content and streamflows are running well above normal for this time
of year.

The National Weather Service in Huntsville issues a Spring Flood
Potential Outlook each Spring. This product is based on analysis of
soil moisture, river and stream levels, reservoir levels, and future
precipitation patterns. Snow cover in the basin as a whole is
factored into the outlook, if it`s present. A second Spring Flood
Outlook may be issued later in the season if conditions warrant.

.Current Conditions...
Many sites across the area are at least 4 to 5 inches above normal
for the month of February, with a few sites approaching 6 to 7+
inches above normal. With rainfall totals with the ongoing
rainfall/flooding event, several sites across the area are
approaching 12 inches of rain for the month of February, which
reaches the top 3 or 5 rainfall totals for the month, historically

Soil moisture content is well above normal for this time of year,
running above 70% for much of the area, with a monthly change between
150-200% of normal for this time of year. This lines up well with the
axis of heavy rainfall for the latter half of February from Arkansas
north/eastward into Tennessee, Northern Mississippi and Northern

Looking ahead for the next 3 months, the Temperature Outlook for
March, April, and May moderately favors higher than normal chances
for above normal temperatures across the Hydrologic Service Area
(HSA). The Precipitation Outlook for the same timeframe slightly
favors higher than normal chances of precipitation.

River and stream levels were nearing climatologically low values from
November through January with the lower than expected rainfall
amounts during those months. During February, however, values have
skyrocketed and are now several hundred percent higher than usual
for this time of year. Thankfully, the overly wet pattern of the last
week or two will come to an end, with only light rainfall expected
with storm systems slated to affect the area next week. This break in
the heavy rainfall pattern should help stream and river levels lower
significantly, but likely staying a little higher than normal
baseflow for this time of year.

For reference, the observed daily streamflows as a percent of median
are given below:

Paint Rock River        Woodville  AL         348%
Flint River             Brownsboro AL         761%
Big Nance Creek         Courtland  AL         662%

Most other rivers throughout the HSA are also operating well above
normal operating curves for this time of year, including: Bear Creek
Lake, Cedar Creek Lake, Tims Ford Lake, Tennessee River at
Guntersville/Wheeler/Wilson Lake, and Smith Lake Dam in Cullman.
Reservoir levels are usually held within a normal operating range
throughout the year, but with the heavy rainfall over the past 2
weeks, reservoirs were above these ranges. As a result, water is
being released along the Tennessee River to handle upstream
rainfall/downstream flows from East Tennessee. Over the next few
weeks, reservoir levels should return to the upper end of normal
operating curves for this time of the year.

.7-Day Forecast...
After a really active heavy rainfall pattern over the latter half of
February and into early March, thankfully a somewhat drier pattern
sets up over the next 7 days. We will see a little rain during this
time, but nothing on the order of the 4-6+ rainfall totals we`ve
received in the last 3-4 days. After a cool/sunny/dry weekend across
the Tennessee Valley, another storm system approaches early next
week, but looks to traverse the area quickly. Rainfall totals of
0.25-0.5" are possible with this event, but again, thanks to the dry
period this weekend, this should be able to be mostly absorbed as
area creeks/rivers will have fallen down closer to baseflow values by
this time.

.8-14 Day Outlook...
The break from the heavy rainfall will be generally short-lived next
week as the 8-14 day forecast calls for above normal precipitation
values and below normal temperatures. Exact rainfall amounts this far
out are difficult to discern, however, additional storm systems will
move across the Southeastern U.S., which is typical for us this time
of year. Each round will bring at least some rainfall with it, as
normal rainfall for a week in March is around an inch (summing up to
near 4" for the monthly total).

.Seasonal Outlook for March, April, and May...
The Seasonal Outlook for the next 3 months across the Tennessee
Valley favor above normal precipitation and temperatures.

.Long Range Probabilistic River Forecasts...
The long-range probabilistic river forecasts show the chances of
exceedence of values above certain thresholds (Minor, Moderate, and
Major Flood Stage). Below are those probabilities (and their
associated values per stage):

Site             Chance of exceedence: Minor     Moderate     Major
Big Nance Creek/Courtland               95+%        36%         20%
Elk River at Fayetteville               95+%         9%         <5%
Flint River at Brownsboro               95+%       95+%         <5%
Paint Rock at Woodville                 95+%        13%         <5%

Flood stages are as follows for each site:

Big Nance Creek: Minor (14ft), Moderate (16ft), and Major (19ft).
Elk River: Minor (17.5ft), Moderate (20.7ft), and Major (26ft).
Flint River: Minor (17ft), Moderate (19ft), and Major (22ft).
Paint Rock River: Minor (16ft), Moderate (19ft), and Major (22ft).

The Flood Potential for Spring 2018 is above average across the
entire WFO Huntsville Hydrologic Service Area (HSA). Given soil
moisture values well above normal, the rainfall that falls today will
continue to produce at least minor flooding in areas that are
already saturated from recent rainfall. Thankfully, a drier period
will return from Friday through the weekend with sunny but cool
conditions across the area. This should help to somewhat dry out at
least the upper layer of soils across the area, and the timeframe
should allow rivers/creeks/streams to fall closer to normal baseflow
this time of year. Overall, flooding concerns will lessen as we head
from Spring into Summer, which is typical for this area.

This product is designed to give the public and emergency management
officials an outlook on the potential for flooding during the next
few months, the traditional flooding season. This and other
hydrologic information is available on the Internet at
weather.gov/huntsville under the Rivers and Lakes AHPS menu.

There are no traditional Spring Flood Awareness Weeks anymore, as
there has been a push to move to more seasonal awareness of threats
in lieu of individual weeks.

Stream and rainfall data are provided by the Tennessee Valley
Authority, the U.S. Geological Survey, the U.S. Army Corps of
Engineers, and the National Weather Service Cooperative and Backyard
Weather Observers. We thank these partners for their valuable data!


For questions or comments about this outlook, please contact:

Chelly Amin
Hydrology Program Manager
256.890.8503 ext. 225


Chris Darden
Meteorologist in Charge
256.890.8503 ext. 222



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