Flood Potential Outlook
Issued by NWS Buffalo, NY

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Winter/Spring Flood Potential Outlook
National Weather Service Buffalo NY
630 AM EST Thu Feb 15 2018

...ABOVE NORMAL FLOOD RISK THROUGH MARCH 1ST...

This is the fourth flood potential outlook of the 2018 season. 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 prolonged period of above normal temperatures in January melted
the majority of the snow in the Genesee, Allegheny, and Buffalo
Creeks basins. This flushed out most river and creek ice, with the
exception of some thick blocks of ice along the shores. This also
provided a clean slate for snow pack, with the exception of a few
sites in the Buffalo creeks headwaters where some of the deepest
previous snowpack survived. The snowpack going into this period was
much deeper across the Black River basin, and a significant snow
pack was maintained across the higher terrain of the Tug Hill
and Adirondacks.

During the first half of February, a much colder pattern provided
several opportunities for snow to re-establish the snow pack. This
pattern brought snow water equivalent (SWE) values to near normal
across the Buffalo Creeks basin with slightly below normal amounts
in the Genesee and Allegheny river basins. With Lake Ontario still
unfrozen, the heaviest snow during the period was due to lake effect
which occurred east of Lake Ontario in the Black River basin. SWE
averages about 125 percent of normal in the Black River basin, with
over 9 inches in some locations.

River and creek ice has re-formed but temperatures were not cold
enough to produce a solid and thick ice cover in most areas. Even
so, there is patchy ice cover which is 3 to 6 inches thick in some
locations. This may result in some ice jams, though the amount of
ice is less than if there was solid ice coverage.

The following is a summary of the conditions by basin as of early
Thursday morning, February 15th:

...BUFFALO AREA CREEKS / LAKE ERIE BASIN...
.SNOW COVER..........4 to 10 inches.
.WATER EQUIVALENT....1 to 2 inches, isolated up to 4 inches.
.CREEK FLOWS.........Near normal.
.CREEK ICE...........Variable, shore ice, frozen on some areas 3-5
                     inches thick.
.GROUND FROST........5 to 9 inches.
.GROUND STATE........Mainly frozen.

...GENESEE RIVER BASIN / FINGER LAKES / ROCHESTER AREA...
.SNOW COVER..........T to 4 inches.
.WATER EQUIVALENT....0.5 inches to 1 inch.
.RIVER/CREEK FLOWS...Near normal.
.RIVER/CREEK ICE.....Variable, shore ice, frozen on some areas 3-5
                     inches thick.
.GROUND FROST........4 to 9 inches.
.GROUND STATE........Mainly frozen.

...ALLEGHENY RIVER BASIN...
.SNOW COVER..........T to 4 inches.
.WATER EQUIVALENT....Around an inch.
.RIVER/CREEK FLOWS...Near normal.
.RIVER CREEK ICE.....Variable, mainly shore ice.
.GROUND FROST........Up to 5 inches.
.GROUND STATE........Mainly frozen.

...BLACK RIVER BASINS / TUG HILL...
.SNOW COVER..........Around a foot, with 2 to 3 feet on the Tug Hill
                     and Adirondacks.
.WATER EQUIVALENT....2 to 5 inches, 6 to 10 inches on the Tug Hill
                     and Adirondacks.
.RIVER/CREEK FLOWS...Near normal.
.RIVER/CREEK ICE.....Mainly frozen, moderate thickness.
.GROUND FROST........6 to 12 inches.
.GROUND STATE........Frozen.

...TEMPERATURE AND PRECIPITATION OUTLOOK...

Temperatures and precipitation are highly likely to be above normal
during the period. The period will start off with above normal
temperatures but it will cool to mostly below freezing over the
weekend. After this, there is high forecast confidence in a warm
pattern for most of next week. This pattern is shown by nearly all
long range model guidance, with high temperatures likely to top 50
degrees several days with 60 not out of the question. There is still
some uncertainty with rainfall amounts. A frontal boundary is
forecast to stall to our west with waves of low pressure expected to
periodically track along this boundary and bring periods of rain to
our region. At this time the heaviest rain is likely to be to our
southeast across the Ohio River Valley, however there is a risk this
may shift into our region.

Looking further ahead to the end of February there is a bit less
forecast confidence. In general a zonal pattern with near to above
normal temperatures is favored with frequent chances for
precipitation.

Both the 6 to 10 day and 8 to 14 day outlooks are for above normal
temperatures and precipitation. For the 6 to 10 day outlooks the
chance for above normal temperatures is above the 90 percent
confidence level.

...FLOOD POTENTIAL OUTLOOK...

The flood risk for the next two weeks is above normal.

The combination of existing snow pack and the likelihood of warm
temperatures and frequent precipitation suggests there is above
normal flood risk for the outlook period.

For early portions of the outlook period the greatest risk is in the
Buffalo creeks, and Allegheny and Genesee River Basins. This is
because warm temperatures will melt the majority of the snow during
this time, and this combined with any precipitation has the
potential to result in flooding. After this, warm temperatures later
in the outlook period will be less relevant since snow pack is
likely to be below normal in these basins. Monitor the latest flood
watch and warning products for the latest information.

For the Black River basin, there is a much more significant snow
pack which will take much longer to melt. Temperatures will not be
as warm in this basin early in the outlook period, which will
probably help ripen the snow pack but not melt it completely.
However, looking to next week and later in the outlook period
another round of much above normal temperatures is expected. This
alone will cause significant rises in flows in the Black River
Basin. Meanwhile there will be frequent opportunities for
precipitation during this time, which may combined with run-off from
snow melt to potentially cause flooding. So for the Black River
basin the greatest risk for flooding is next week and beyond due to
the deeper snow pack.

...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 March 1st.

$$

KA



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