Flood Potential Outlook
Issued by NWS Huntsville, AL

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Hydrologic Outlook
National Weather Service Huntsville AL
1001 AM CST Thu Mar 2 2017

...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 below average flood potential for
Spring 2017. Though recent rainfall in December and January was at or
slightly above normal for the beginning of Winter, with the ongoing
drought conditions in place across central/eastern portions of the
area, this will help to keep widespread flooding conditions at bay
for the upcoming Spring. Current soil moisture values are well below
normal for this time of year, and the rainfall events that we`re
seeing are only really affecting the upper several inches of soil
across the area (not long-term storage overall noted in the deeper
soil moisture layer as a whole). In the wake of these rainfall
events, river and creek levels across the area quickly fall back to
or below normal baseflow, which is helping to keep drought conditions
in place across the area. Long-term storage of moisture isn`t
occurring as quickly as it did in late 2015 and early 2016 because
the rainfall events aren`t occurring as often and the amounts aren`t
as high as a year ago.

Though the overall consensus is for a below average flood season, exact
rainfall amounts and storms repeatedly affecting the same locations
may produce flooding at times this Spring.

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 is present. A second Spring Flood
Outlook may be issued later if conditions warrant.

.Current Conditions...
After a prolonged dry period and exceptional drought from the Summer
into Fall of 2016, a wetter pattern prevailed for late November and
continued throughout much of December. January 2017 saw above normal
rainfall across much of the region as well, with only a few locations
observing near or slightly below normal rainfall for the month.
February was drier overall than January, with many locations across
Northern Alabama and Southern Middle Tennessee about 1 to 3 inches
below normal. A few locations were between 3 and 4 inches below
normal for the month across portions of Northwestern Alabama toward
the Alabama/Mississippi State line.

Soil moisture content varies across the area. Following in line with
the most recent Drought Monitor issuance, drier soils are present in
southern/eastern counties (Cullman, Marshall, and Dekalb). Further
north and west across portions of Northwestern Alabama, conditions
are wetter, and as a result, drought conditions there are much less
severe. With below normal rainfall and above normal temperatures
expected generally over the next few months, this will cause drought
conditions to linger barring several heavy rainfall events occurring
(and improving conditions) through the Spring.

As of yesterday, recent rainfall has caused many basins across the
area to rise above the normal daily streamflows for this time of
year. Below are a few of these sites as a percentage of median
values:
3/1 values

Paint Rock River near Woodville       352%
Flint River at Brownsboro             251%
Big Nance Creek at Courtland          226%

Looking ahead for the next 3 months...the Temperature Outlook for
March, April, and May moderately favors above normal temperatures
for the Hydrologic Service Area (HSA). The Precipitation Outlook for
the same timeframe favors equal chances for above, near, or
below-normal rainfall.

River and stream levels rebounded nicely by the end of December
2016, and this trend continued into January 2017. While levels
generally fell between rainfall events, many levels were well above
normal when rainfall events did occur. This even led to several
instances of river flooding by the end of January. February overall
was drier than January, with river and creek levels falling back down
to near or slightly below normal baseflow values for this time of
year. The few rainfall events that were observed in February briefly
raised levels in area creeks, streams, and rivers, but values quickly
fell afterwards.

Across Alabama and Tennessee, river and stream levels are averaging
near normal, with a handful of sites averaging well above and well
below normal for this time of year. Bear Creek, Nickajack, Wheeler,
Wilson, and Pickwick Reservoirs/Dams are all operating within normal
levels for this time of year. Little Bear and Cedar Creek Reservoirs
are operating below normal levels. Tims Ford is operating above its
Flood Guide for this time of year, and Guntersville, and Smith Lake
Dams/Reservoirs are all operating well above their normal ranges of
values for late Winter.

The outlook for river levels, soil moisture, and groundwater through
early April is for a continuation of current conditions, leading to a
below average flood potential for Spring 2017. A mix of
near/above/below normal rainfall amounts over the coming months will
at times exacerbate the ongoing drought conditions, or on the other
hand, produce brief rises on area creeks, streams, and rivers.
This will heavily depend on the track/strength of individual storms
systems that occur through late April and into May. As such, river
levels, soil moisture, and groundwater levels will vary during this
time.

.7-Day Forecast...
After the moderate to heavy rainfall on Tuesday and the severe
weather yesterday (Wednesday) across Northern Alabama and Southern
Middle Tennessee, high pressure will build back into the area for the
rest of this week and weekend, as well as the early week ahead.
Daytime high temperatures will moderate back into the middle/upper
60s ahead of an approaching cold front next week, with morning lows
currently in the 30s dipping into the 20s by Saturday morning.
Thankfully, morning lows will then moderate back to near 60 degrees
by Monday/Tuesday of next week. In the wake of the cold front next
week, morning lows will fall into the lower 40s by the latter half of
the week, which is more seasonable for this time of year.

The recent rainfall will keep river and creek levels above normal
baseflow for this time of year for the next few days, but with the
drier conditions expected over the next 5 days or so, values will
quickly fall as runoff decreases rapidly across the area.

.8-14 Day Forecast...
The eight to fourteen day outlook issued by the Climate Prediction
Center calls for near normal temperatures, but to the west, much
higher than normal temperatures are expected. Precipitation-wise,
below normal rainfall is favored for March 7th through the 13th.

.Monthly Outlook for March...
The outlook for the month of March is also issued by the Climate
Prediction Center. It moderately favors above normal temperatures
and precipitation through April 1st.

.Seasonal Outlook for the Spring...
The outlook for the Spring season, March through May, issued by the
Climate Prediction Center moderately favors (40%) above normal
temperatures, with equal chances for below, near, or above normal
rainfall. Again, this all will depend heavily on the exact track of
storm systems across the area during this time.

.Long Range Probabilistic River Forecasts...
Probabilities of long-term flood potential for the Tennessee Valley
tributaries are provided weekly by the Lower Mississippi River
Forecast Center in Slidell Louisiana. These probabilities should be
used for planning purposes and factor in historical conditions in
multiple scenarios. They do not include future rainfall.

These probabilities indicate a below average flood potential for the
90-day period ending May 30th 2017. In fact, a majority of the
forecast points within the WFO Huntsville Hydrologic Service Area
have less than a 25% chance of exceeding Flood Stage during this
time. Several have less than a 10% chance. As such, the traditional
chart that shows individual probabilities will not be included with
this Spring Flood Outlook given such very low probabilities.

That said, these figures and probabilities are for planning purposes
only. Do not use them as a means of ignoring flood threats that may
occur with heavy rainfall. If Flood Outlooks, Watches, or Warnings
are issued...take immediate action to protect your life and
property!

.Wrapup...
The Flood Potential for Spring 2017 is below average for the entire
WFO Huntsville Hydrologic Service Area. Soil moisture values continue
to remain relatively low, despite several rainfall events scattered
from late Fall through this point in Winter 2017. River and creek
levels overall are also low for this time of year, and only briefly
rise in the wake of these rainfall events. They quickly fall back to
near normal or below normal values with drier conditions in place as
the long-term storage of moisture across the area is lacking. This
is helping to keep drought conditions lingering across the area, with
drier conditions noted in the southern/eastern portions of the area
(Cullman, Marshall, and Dekalb Counties). Every portion of the WFO
Huntsville Hydrologic Service Area is included in some form of
Drought Designation from the weekly Drought Monitor issuance, even if
it`s the lowest inclusion of Abnormally Dry (D0) Conditions in
portions of Northwestern Alabama.

It`s hopeful that rainfall events will be spaced evenly enough
through Spring 2017 to keep the drought conditions from worsening, as
well as to help retain moisture heading into the traditionally drier
time of year for Summer and back into the Fall of 2017.

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 in the Tennessee Valley.
This and other hydrologic information is available on the internet
at http://weather.gov/huntsville under the "Rivers and Lakes" tab in
the center of the screen above the Graphicast.

There is no official Spring Flood Awareness Week anymore. Instead of
individual weeks of awareness, the NWS is observing more `seasonal`
awareness, titled Severe Weather Awareness Week. Last week, Flood
Safety and Awareness Day was observed, covering numerous topics
about the subject, and how to prepare for and stay safe from
flooding situations.

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
256.801.3096

or

Chris Darden
Meteorologist in Charge
256.890.8503 ext. 222

$$

Amin



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