Transcript Spring Flood Outlook - Benton County, Minnesota

SPRING FLOOD
OUTLOOK
National Weather Service
Chanhassen - Twin Cities
North Central River Forecast Center
March 6, 2014
[email protected]
952-368-2542
Summary Up Front
• Overall, the spring flood threat west of the Mississippi remains
near or below historical average
• East of the Mississippi, the St. Croix, Chippewa and Eau Claire
basins have a higher probability of flooding (50-60%)
• Due to higher water content in the snowpack over WI/northeast MN
• As always…the true threat lies in how the spring temperatures
and rainfall hit us – currently, long range models show a good
likelihood of below normal temperatures and rainfall
Background: Precipitation
since last briefing (Feb 19)
Since last
outlook: added
.50 – 1.0 inch of
water to the
snowpack
Almost no
melting
Background: Precipitation
Last 30 Days
About 1 to 2
inches of water
equivalent has
fallen over
eastern MN/ WI
during the last
30 days
Less than one
inch in western
MN
Shown as percent of normal precipitation
Source of map: Regional Climate Centers
Background: Precipitation
Dec/Jan/Feb Percent of Normal
Winter
precipitation has
been well above
normal north
and east of MSP
(4 to 7 inches)
Below normal
over western
MN (1 to 3
inches)
Source of map: Regional Climate Centers
Background: Precipitation
Snow Water Equivalent (SWE)
SWE on the ground:
• < 2 in. west and
southwest
• 3-4.5 in. MSP area
• 4-6 in. WI portion
Background: Precipitation
Snow Water Equivalent (SWE) Ranking
Summary of graphic:
SWE falls in the middle of
those observed (30-70
percent) over the past
60+ years for much of
our area
Some basins in
western/northern WI and
northern MN near the
most seen in 60+ years
Weather Outlook
8–14 Days
• Temperatures: likely below normal, somewhat moderate
• Precipitation: No clear signal
Weather Outlook
90 days – March through May
Temps: Likely
below normal
through the spring
Precipitation (not
shown): no clear
indication of above
or below normal
Other Factors
Soil Moisture: Near to below normal over most
of area, but higher than last year at this time
Frost Depth: Generally 20 to 40 inches over the
area, except well below 6-8 feet under pavement.
Depth is greatest where snowpack is light or bare
ground, shallower where snowpack has insulated
the ground
River Ice: Thick layers of ice on most rivers;
breakup jams will be a concern
Flood Outlook
Mar-Apr-May 2014
Forecasts take into account all current conditions, 7-day forecast weather,
and climatological normals for the remainder of the spring.
Orange: 50% or greater
chance of minor
flooding
Red: 50% or greater
chance of moderate
flooding (none in MPX
area)
In MPX area …the main
threats are:
• Chippewa at Durand
• Eau Claire at Fall
Creek
• St. Croix at Stillwater
• Minnesota at Savage
(backwater from the
Miss. R.)
Flood threat is greater in
the Red River of the
North (but fairly typical)
Flood Outlook – Durand WI
Black Line is current forecast: shows about a 75 percent chance of minor flooding,
compared to about 50 percent chance in a normal year (blue line). About a 35 percent
chance of moderate flooding, compared to 15 in a normal year.
Flood Outlook – Fall Creek WI
Black Line is current forecast: shows about a 55 percent chance of minor flooding,
compared to about 30 percent chance in a normal year (blue line). About a 40 percent
chance of moderate flooding, compared to 15 percent in a normal year.
Flood Outlook – Stillwater MN
Black Line is current forecast: shows about a 60 percent chance of minor flooding,
compared to about 20 percent chance in a normal year (blue line). About a 40 percent
chance of moderate flooding, compared to 17 percent in a normal year.
Threat Factors
Main things to watch for that would increase flood threat…
• Extended period of well above normal temperatures, staying above
freezing at night
• Normal highs in lower 30s early March, close to 50 by April 1
• Moist air melts snow much faster than dry air, so look for dewpoints
well above freezing when the air is warm
• Any major rainfall event that adds a significant amount of water to
wet snow
Things to watch for that keep the flood threat manageable…
• Temps in the 30s to mid 40s, dropping below freezing at night
• Below to average precipitation – light to moderate snow or light rain
is fine
• Dry air – dewpoints in the teens and 20s.
Summary
• Overall, spring flood threat over MPX area of responsibility is
near to below historical average, but has increased slightly
since late February
• EXCEPTIONS are the Chippewa and Eau Claire basins in
Wisconsin, and St. Croix in MN and WI
• Also the lower Minnesota R around Savage due to backwater from
the Mississippi R
• As always…the true threat lies in how the spring weather
unfolds
More Info?
• Text version of this outlook available at
• http://forecast.weather.gov/product.php?site=NW
S&product=ESF&issuedby=MSP
• Weather information:
• http://www.crh.noaa.gov/mpx/
• River information:
• http://water.weather.gov/ahps2/index.php?wfo=
mpx
• For further information or if you have questions,
please contact us at the NWS Twin Cities office
• 952-361-6671 (forecaster desk, 24/7)
• 952-368-2542 (Craig Schmidt, Service Hydrologist)
[email protected]