Flood Potential Outlook
Issued by NWS Buffalo, NY

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Winter/Spring Flood Potential Outlook
National Weather Service Buffalo NY
905 AM EST Sat Jan 6 2018

...NEAR NORMAL FLOOD RISK THROUGH JANUARY 18TH...

This is an update the first flood potential outlook of the 2018
season. The hydrologic outlook is being updated to reflect a
change in the forecast with warmer temperatures now expected for a
portion of the outlook period.

Flood outlooks will be issued every two weeks into early
spring to summarize basin conditions and to assess the potential
for flooding. The outlooks are based on current and forecast
hydrometeorological conditions. This includes snow cover and water
equivalent, creek and river levels and the amount of ice on them,
along with the expected conditions during the next two weeks.

...CURRENT CONDITIONS SUMMARY...

A cold pattern became well established from early December onward,
resulting in frequent lake effect snows so far this season.

Snow Water Equivalent (SWE) is above normal across the entire
region. It varies considerably since the vast majority of snow has
been lake effect, and therefore somewhat localized in nature.
However, due to the frequent events there is snow on the ground
across the entire region. As is typically the case, the deepest snow
pack is across the Black River Basin. There is already over 4 feet
of snow on portions of the Tug Hill, which is well above normal for
this early in the season.

Most area creeks are at least partially frozen, with patchy ice on
larger waterways. Temperatures were much colder across the Black
River basin, resulting in thick ice cover on most rivers and
creeks.

The following is a summary of the conditions by basin as of
early Thursday morning, January 4th:

...BUFFALO AREA CREEKS / LAKE ERIE BASIN...
.SNOW COVER..........8 to 16 inches.
.WATER EQUIVALENT....1 to 4 inches.
.CREEK FLOWS.........Near normal.
.CREEK ICE...........Mostly frozen.
.GROUND FROST........6 to 12 inches.
.GROUND STATE........Frozen.

...GENESEE RIVER BASIN / FINGER LAKES / ROCHESTER AREA...
.SNOW COVER..........5 to 10 inches.
.WATER EQUIVALENT....0.5 to 2 inches.
.RIVER/CREEK FLOWS...Near normal.
.RIVER/CREEK ICE.....Mostly frozen.
.GROUND FROST........4 to 8 inches.
.GROUND STATE........Frozen.

...ALLEGHENY RIVER BASIN...
.SNOW COVER..........10 to 20 inches.
.WATER EQUIVALENT....2 to 3 inches.
.RIVER/CREEK FLOWS...Near normal.
.RIVER CREEK ICE.....Mostly frozen.
.GROUND FROST........6 to 12 inches.
.GROUND STATE........Frozen.

...BLACK RIVER BASINS / TUG HILL...
.SNOW COVER..........1 to 2 feet, 2 to 4 feet on the Tug Hill.
.WATER EQUIVALENT....2 to 4 inches, 4 to 8 inches on the Tug Hill.
.RIVER/CREEK FLOWS...Near normal.
.RIVER/CREEK ICE.....Frozen.
.GROUND FROST........12 to 18 inches.
.GROUND STATE........Frozen.

...TEMPERATURE AND PRECIPITATION OUTLOOK...

The region will remain in a cold pattern over the next week with
temperatures well below freezing for the majority of the time.
Below normal temperatures will also increase ice thickness with
frequent opportunities for lake effect snow which is likely to add
to the snow pack.

Looking further ahead to the week of January 11th through January
18th, the latest long range model guidance is significantly
warmer than it was a couple days ago. The latest 6 to 10 day
outlook from the Climate Prediction Center is calling for above
normal temperatures and above normal precipitation.

More specifically, a significant warm up is likely on the 11th
and 12th, followed by a return to cold weather. At this time, it
appears there will not be significant rainfall with this warm up
with generally a half inch or less of rain expected during this
period of warmer temperatures.

...FLOOD POTENTIAL OUTLOOK...

Flood risk during the next two weeks is near normal.

Although SWE is above normal, this is somewhat offset by primarily
below normal temperatures during the period. The main concern is
that there likely will be two days of above normal temperatures in
around January 11th and 12th. Although heavy rainfall is not
likely to come with this warmer weather, the combination of warm
temperatures and light rainfall does pose some risk for flooding.

The greatest risk for flooding is ice jam flooding in the Buffalo
creeks, where a prolonged warm up can cause ice to break up and
eventually jam. Ice will be unusually thick, so it may take a bit
longer period of warm temperatures than usual to cause a break up.
There is also a lesser risk for general flooding from a
combination of snow melt and rainfall, however the snow pack is
not ripe which will delay run-off.

After the brief warm up late in the week, temperatures are
likely to fall below normal again with a diminishing risk for
flooding later in the outlook period.

...ADDITIONAL INFORMATION...

Real time river information and probabilistic forecast for
specific locations along rivers across Western New York can be
found on the internet at www.weather.gov/buf. Since conditions can
change, please refer to the latest flood watches, warnings, and
statements for additional information.

Thank you to all the observers and agencies which have helped
gather data in support of this outlook. The next Winter/Spring
Flood Outlook will be issued on January 18th.

$$

Apffel



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