spring flood outlook
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
National Weather Service
Chanhassen - Twin Cities
North Central River Forecast Center
SPRING FLOOD OUTLOOK
March 6, [email protected]
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: Precipitationsince last briefing (Feb 19)
Since last outlook: added .50 – 1.0 inch of water to the snowpack
Almost no melting
Background: PrecipitationLast 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
Source of map: Regional Climate Centers
Shown as percent of normal precipitation
Background: PrecipitationDec/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: PrecipitationSnow Water Equivalent (SWE)
SWE on the ground:•< 2 in. west and southwest• 3-4.5 in. MSP area• 4-6 in. WI portion
Background: PrecipitationSnow 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 Outlook8–14 Days
• Temperatures: likely below normal, somewhat moderate• Precipitation: No clear signal
Temps: Likely below normal through the spring
Precipitation (not shown): no clear indication of above or below normal
Weather Outlook90 days – March through May
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
Other Factors
Orange: 50% or greater chance of minor floodingRed: 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 OutlookMar-Apr-May 2014
Forecasts take into account all current conditions, 7-day forecast weather, and climatological normals for the remainder of the spring.
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 – Durand 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 – Fall Creek WI
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.
Flood Outlook – Stillwater MN
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=NWS&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]