Flood Potential Outlook
Issued by NWS Buffalo, NY

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Winter/Spring Flood Potential Outlook
National Weather Service Buffalo NY
452 PM EDT Thu Mar 21 2019

...NEAR NORMAL FLOOD RISK THROUGH APRIL 4TH...

This is the sixth flood potential outlook of the 2019 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...

Warm temperatures, particularly on March 13th-15th, have resulted in
considerable snow melt during the past couple weeks. The majority
of snow and ice has already melted south of Lake Ontario. There
is some patchy snow in sheltered locations, but snow water
equivalent values (SWE) are negligible.

There still remains a significant snow pack in the Black River
Basin, particularly on the Tug Hill Plateau and across the higher
terrain of the Adirondacks. Despite some melting over the past
couple weeks, SWE values are still near normal for the Black
River Basin.

The warm temperatures did break up and flush out a significant
amount of river and creek ice. There is little to no ice remaining
on creeks and rivers south of Lake Ontario. Warmer temperatures
and some rain also flushed out a lot of the ice in the Black River
basin, with only patchy areas of ice and shore ice remaining.

The following is a summary of the conditions by basin as of Thursday
morning, March 21st:

...BUFFALO AREA CREEKS / LAKE ERIE BASIN...
.SNOW COVER..........Less than an inch.
.WATER EQUIVALENT....Less than a tenth of an inch.
.CREEK FLOWS.........Slightly below normal.
.CREEK ICE...........Little to none.
.GROUND FROST........Down to 9 inches, surface thawed.
.GROUND STATE........Variable, saturated where not frozen.

...GENESEE RIVER BASIN / FINGER LAKES / ROCHESTER AREA...
.SNOW COVER..........Less than an inch.
.WATER EQUIVALENT....Less than a tenth of an inch.
.RIVER/CREEK FLOWS...Near normal.
.RIVER/CREEK ICE.....Little to none.
.GROUND FROST........Down to 6 inches, surface thawed.
.GROUND STATE........Variable, saturated where not frozen.

...ALLEGHENY RIVER BASIN...
.SNOW COVER..........Little to none.
.WATER EQUIVALENT....Little to none.
.RIVER/CREEK FLOWS...Slightly below normal.
.RIVER CREEK ICE.....Little to none.
.GROUND FROST........Down to 6 inches, surface thawed.
.GROUND STATE........Variable, saturated where not frozen.

...BLACK RIVER BASINS / TUG HILL...
.SNOW COVER..........Less than 3 inches, except 1-2 feet on the Tug
Hill and Adirondacks.
.WATER EQUIVALENT....Less than an inch, except 4 to 8 inches on
the Tug Hill and Adirondacks.
.RIVER/CREEK FLOWS...Slightly below normal.
.RIVER/CREEK ICE.....Variable.
.GROUND FROST........12 to 24 inches, surface thawed in spots.
.GROUND STATE........Variable, saturated where not frozen.

...TEMPERATURE AND PRECIPITATION OUTLOOK...

A strengthening Nor`easter will bring cold conditions and some snow
to the area Friday and Saturday. Temperatures will fall during the
day Friday, and largely remain near or below freezing through
Saturday. Meanwhile this system will bring some generally light to
moderate snow to areas south of Lake Ontario, with a more
significant snowfall east of Lake Ontario where around an inch of
SWE is likely to be added.

After this, it will be a drier pattern with limited precipitation
through the middle of next week. Sunday will be warmer, but then
colder air will build in with below normal temperatures expected for
the first half of next week.

It is likely that temperatures will average above normal for the
last few days of March, followed by below normal temperatures the
first few days of April. This is because long range model
guidance shows a broad southwesterly flow with warmer
temperatures, followed by a low pressure system and a cold front.
The timing and track of this are uncertain at this timeframe. The
Climate Prediction Center 8 to 14 day outlook is for near normal
temperatures, and above normal precipitation.

...FLOOD POTENTIAL OUTLOOK...

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

There are offsetting factors, which leads to this conclusion.
Overall there is a very low risk for flooding during the first
week of the outlook period. The most significant precipitation
will fall as snow heading into the weekend, and then it will be
cool and mainly dry through the middle portion of next week.

This wintry pattern is likely to add to the snow pack heading
into latter portions of the outlook. Snow south of Lake Ontario
should melt gradually and not initially pose a flood risk, but
this will result in saturated soil and above normal flows on
creeks. Meanwhile, the additional snow is likely to leave SWE
above normal for the Black River Basin by the middle of next
week.

This will then be followed by a period of warmer temperatures
late next week which will accelerate snow melt, especially in the
Black River Basin. This is likely to be followed by a significant
system, which is likely to bring at least some rain to the area.
Rainfall amounts and timing are still uncertain this far off, but
it may pose a risk for flooding if there is significant rainfall
along with the warm temperatures.

Although the risk is very low early in the outlook period, the
risk with the potential system late in the outlook period is
significant enough to justify a near normal flood risk for 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 April 4th.

$$

Apffel



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