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FGUS71 KBUF 181449
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Winter/Spring Flood Potential Outlook
National Weather Service Buffalo NY
1049 AM EDT Thu Mar 18 2021

...BELOW NORMAL FLOOD RISK FOR WESTERN NEW YORK THROUGH APRIL 1ST...
...NEAR NORMAL FLOOD RISK FOR THE BLACK RIVER BASIN THROUGH 
   APRIL 1ST...

This is the sixth flood potential outlook of the 2021 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 weather between March 8th and 12th melted a significant portion
of the snowpack. For basins south of Lake Ontario, there is hardly
any snow pack in place with snow water equivalent (SWE) values
negligible. The warm up also flushed out all of the river and creek ice
in these basins. As a result, temperatures will be somewhat irrelevant
for these basins since the snow is all gone.

Snow still remains in the Black River Basin, but most of the snowpack 
is confined to higher terrain on the Tug Hill and the Western 
Adirondacks. The warm weather melted most of the snow pack across lower 
elevations, but the snow was so deep across higher terrain that 
significant SWE values remain across a little less than half of the 
basin. This limited snow coverage limits the potential quick run-off. 
SWE values in the Black River basin are below normal for this date,
averaging only around 80 percent of the normal value. There also may 
be limited river and creek ice in place, however this has weakened 
considerably due to higher sun angles and warmer weather so it will 
be less likely to cause ice jams.

The following is a summary of the conditions by basin as of Thursday 
morning, March 18th:

...BUFFALO AREA CREEKS / LAKE ERIE BASIN...
.SNOW COVER..........None, except patches up to 2 inches.
.WATER EQUIVALENT....None, except highly localized up an inch.
.CREEK FLOWS.........Below normal.
.CREEK ICE...........None. 
.GROUND FROST........Less than 3 inches.
.GROUND STATE........Frozen in spots otherwise saturated.

...GENESEE RIVER BASIN / FINGER LAKES / ROCHESTER AREA...
.SNOW COVER..........None.
.WATER EQUIVALENT....None.
.CREEK FLOWS.........Near normal.
.CREEK ICE...........None. 
.GROUND FROST........Less than 3 inches.
.GROUND STATE........Frozen in spots otherwise saturated.

...ALLEGHENY RIVER BASIN...
.SNOW COVER..........None.
.WATER EQUIVALENT....None.
.CREEK FLOWS.........Near normal.
.CREEK ICE...........None. 
.GROUND FROST........Less than 3 inches.
.GROUND STATE........Frozen in spots otherwise saturated.

...BLACK RIVER BASINS / TUG HILL...
.SNOW COVER..........None, increasing to 1 to 2 feet on the Tug 
                     Hill and Adirondacks.
.WATER EQUIVALENT....None, increasing to 3 to 7 inches on the Tug
 Hill and Adirondacks.
.RIVER/CREEK FLOWS...Near normal.
.RIVER/CREEK ICE.....Patchy ice in spots, some thick chunks but is
                     weakened from higher sun angle and 
                     warmer weather.
.GROUND FROST........Less than 6 inches.
.GROUND STATE........Mainly frozen.

...TEMPERATURE AND PRECIPITATION OUTLOOK... 

Low pressure passing by to the south will bring some rain or wet
snow to the area today, with the greatest amounts of precipitation
falling across the Western Southern Tier into portions of the
Allegheny and Genesee River basins. Precipitation amounts will be 
modest, averaging a quarter to a half inch across the Western 
Southern Tier to less than a quarter inch north of this.

High pressure will build across the region on Friday, kicking off a 
long stretch of dry weather which will last through Tuesday next 
week. Little, if any, precipitation is expected during this time. 
Meanwhile, Friday will start off on the cool side with a warming 
trend during the period. By early next week high temperatures will 
be in the 50s across the Black River basin, with highs in the 50s
and 60s elsewhere.

After this, there will be a series of storm systems which pass close 
to our area. The pattern aloft will favor systems passing by to the 
west, which would generally maintain warm weather and would more
likely produce rain instead of snow. Forecast confidence lowers 
with time, but in general the most concerning timeframe is 
March 25th - 29th when range model guidance suggests the potential 
for a significant rain producing system somewhere in the region. 
Even so, the overall risk of heavy rainfall in our area is limited 
with the chance of rainfall amounts exceeding 2 inches less than 
25 percent.

The latest Climate Prediction Center (CPC) 8 to 14 Day Outlook 
strongly favors above normal temperatures and it also favors above 
normal precipitation.

...FLOOD POTENTIAL OUTLOOK... 

Through April 1st, the risk for flooding is below normal for the 
Buffalo Creeks, and the Allegheny and Genesee River basins and
near normal for the Black River basin.

The flood risk for all basins is low through March 24th. This is 
because there will be an extended period with dry weather during 
most of this time. However, the warmer weather will continue to 
melt off snow pack in the Black River basin which will result in 
high but within bank flows heading into late next week.

Warm weather is expected to continue later into the outlook period.
This will not be a factor for most basins where the snow pack 
will be all gone. However, there still will be some snow and 
and potentially run-off from melting in the Black River basin. This 
will make the basin somewhat vulnerable to flooding, especially if
there is a significant rain producing system during this time. 
Snow pack is below normal, but given that a warm and fairly wet
pattern is expected the overall flood risk for the Black River basin
is near normal. The flood risk will largely depend on how much rain 
falls during the period with little doubt that it will be a warm
pattern. 

It's difficult to completely rule out an unusually strong rain 
producing system late in the outlook period so even though the flood 
risk is below normal for other basins it is still non-zero. Always 
be sure to monitor the latest forecast.

$$

Apffel