Flood Potential Outlook
Issued by NWS Huntsville, AL

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Hydrologic Outlook
National Weather Service Huntsville AL
1211 PM CST Thu Mar 7 2019

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

The flood potential for the Tennessee Valley of Northern Alabama and
Southern Middle Tennessee favors above average flood potential for
Spring 2019. Since December 2018, much of the Tennessee Valley has
had 15 to 30 inches of rainfall, with 10-15 inches of that occurring
over the past 2 weeks. This caused widespread moderate to major
flooding at nearly all of our river forecast points across the area,
and a few points on the Tennessee River crested at their "regulated
flood of record," which means it was the highest values that have
ever occurred since the installation of the dams on the Tennessee
River. While most of the points have finally fallen below Flood
Stage, there is residual flooding still ongoing on the Tennessee
River where a few points just fell from Moderate Flood down into
Minor Flood over the past day or two. With no pattern change in
sight, additional rounds of moderate/heavy rainfall are expected
every few days over at least the next couple of weeks and this will
only further aggravate/add to any lingering flooding across the
area.

As a result, soil moisture and streamflows are running well above
normal for this time of year, so even if a little rain occurs with a
system, it converts wholly to runoff and exacerbates any lingering
flooding issues.

The National Weather Service in Huntsville issues a 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...
Officially, February was the wettest February on record at
Huntsville, with 13.63" recorded, which was 8.79" above normal. The
same was true for Muscle Shoals, totaling 14.13" for February, which
was 9.47" above normal. This was also the wettest Winter on record
(Dec. 2018-Feb.2019) for Huntsville, with 30.58" recorded. With no
pattern change in sight, additional rounds of moderate/heavy rainfall
are expected every few days over at least the next couple of weeks.

Due to the abundance of rainfall that has occurred since December,
there are more than a few sites that are a foot above normal (with a
few pushing almost 14" above normal for this year alone). The sites
that are on the lower end of this list are still on average of 5-7"
above normal for this time of year.

Soil moisture content is well above normal for this time of year,
running above 95% for much of the area, with locations in
Northeastern Alabama and portions of Southern Middle Tennessee in
excess of the 99% mark. This corresponds with the axis of heavy
rainfall/near-record flooding event 2 weeks ago.

For reference, the observed daily streamflows as a percent of median
are given below:
                                     3/6/2019
Paint Rock River Woodville AL          209%
Flint River Brownsboro AL              249%
Big Nance Creek Courtland AL           204%

Looking ahead for the next 3 months, the Temperature Outlook for
March, April, and May 2019 slightly favors higher than normal chances
for above normal temperatures and precipitation for the Hydrologic
Service Area (HSA).

Most other rivers throughout the HSA are also operating well above
normal operating curves for this time of year, including: Bear Creek
Lake, Little Bear Creek Lake, Cedar Creek Lake, and Tims Ford Lake.
Some of these values were the highest anyone has seen in recent
history due to the abundance of rainfall. Other rivers and creeks
that were well above normal operating curves for the year (but have
now fallen back down to within normal range for this time of year
thanks to releases from the Tennessee Valley Authority) include:
Nickajack Lake, Guntersville Lake, Wheeler lake, Wilson Lake and
Pickwick Lake.

Given the record rainfall that occurred in February, the Tennessee
Valley Authority has been feverishly releasing water, as appropriate,
to protect the integrity of the dams along the Tennessee River. To
complicate matters, while releasing water downstream to provide
relief in the headwaters of the Tennessee River in Eastern Tennessee,
the heavy rainfall occurred at different points/basins along the
Tennessee River with our last flood event. This complicated matters
immensely because it threw a wrench in plans to release water at
specific dams to reduce flows upstream. Much thanks to the Tennessee
Valley Authority (TVA) with this last event!

.7-Day Forecast...
For the next 7 days, moderate/heavy rainfall will be possible this
weekend on Saturday ahead of a very strong upper level storm system.
Widespread rainfall amounts upwards of 2 inches is expected, with
isolated higher amounts possible (closer to 3-4"). While a brief
break is expected early next week, another more widespread rainfall
event is on the horizon for mid/late week next week. This next round
of rainfall could bring (worst-case) another 3-5", which would prove
to be catastrophic depending on how quickly it falls.

.8-14 Day Outlook...
The longer-range forecast for Northern Alabama and Southern Middle
Tennessee strongly favors above normal precipitation and below normal
temperatures for the week of March 14th through the 20th. This
signals that a strong cold front would push through the region during
this time, which would give us a break in the wake of the frontal
passage. This would potentially provide a few days of dry conditions
to help allow area streams, creeks, and rivers to return to their
banks (or closer to what normal should be for this time of year).

.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               52%         39%        22%
Elk River at Fayetteville               41%         10%        <5%
Flint River at Brownsboro               57%         24%         5%
Paint Rock at Woodville                 87%         16%        <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 (15ft), Moderate (19ft), and Major (22ft).

.Wrapup...
The Flood Potential for Spring 2019 is above average across the
entire WFO Huntsville Hydrologic Service Area (HSA). Given soil
moisture values well above normal, and recent record rainfall in
February, soggy conditions look to continue for at least the next
week. This will further be exacerbated by a rainfall event on
Saturday, and another more widespread rainfall event mid/late next
week. Rivers, creeks, and streams across the area will respond fairly
rapidly given the wet conditions in place when the rainfall occurs.
While most river points will see Minor Flooding (at least), a few
spots will likely rise back into Moderate Flooding next week.

While a wetter pattern is favored in the short-term, conditions will
gradually begin to dry out as we head into late Spring into the
Summertime. Rainfall will become more spotty in the months ahead,
with flooding concerns eventually waning by then. Until then, though,
we`re going to have a rough spring if the Winter (so far) is any
indication.

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. The seasonal "Severe Weather Awareness
Week" was last week, and had specific days that highlighted either
Areal/River flooding or Flash Flooding.

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

OR

Todd Barron
Warning Coordination Meteorologist
256.890.8503 ext. 223

$$

AMIN



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