Transcript Document

National Weather Service
“Spring” 2014 Flood Update
March 28, 2014
Craig Schmidt, Service Hydrologist
Winter 2013-14
Sixth coldest in
Minnesota history –
five consecutive
months below normal
50 days below zero at
MSP; 77 days below
zero at DLH
100+ inches of snow
at DLH; most of the
state 1-2 feet above
normal; even more in
northern WI
IN SHORT… we
haven’t dealt with a
winter like this in
over 30 years.
Flood Outlook Summary
 Overall, the spring flood threat over Minnesota remains
near historical average…with a catch
 Mississippi slightly above average
 St. Croix above average
 Minnesota R average to below average
 In the Wisconsin basins (Eau Claire and Chippewa), the
threat is rising to above average as we hold onto snow
and move further into spring.
 MOST IMPORTANT POINT: the true threat lies in how April
temperatures and rainfall hit us. We’re holding onto a lot
of water in some basins later into the spring than we
normally do. This makes us more susceptible to
snowmelt combining with warm spring rain as we move
later into the spring.
Background: Snowfall
Water Year to date (inches)
Percent of normal
Good portion of MN above normal this season,
well above normal north and into WI
Background: Snowfall
Snow Depth
Snow mostly gone southwest of I-94; still plenty to
melt further north and east.
Background: Precipitation
Snow Depth change in last week
March 19
March 27
Snow depth decreased over southern and central
parts of area; actually increased far north
Background: Snowfall
Modeled Snow Water Equivalent (SWE)
Mostly gone over southwest half…still 1-2 inches around
the Twin Cities; 3-5 inches in northern WI and MN.
Soil Moisture
(0-72 inch layer)
Near to above
average over much
of the state,
except Minnesota
River basin and
parts of the far
north.
Once thaw occurs,
there is some
room for soil to
absorb water
Other Factors
Frost Depth: Generally 20 to 40 inches over the
area, except 10 to 20 inches around the Twin
Cities. Much deeper still under pavement and
roads.
River Ice: Thick layers of ice on most rivers;
breakup jams will be a concern
Flood Outlook
Climatologically based
Flood outlooks posted in the coming slides
include known conditions up to that point, and
use climatology as the forecast weather
conditions.
Significant deviations in our weather pattern
from climatology would result in different
results. Thus, it will pay to watch our weather
patterns closely through April…
Flood Outlook – Mississippi at St. Cloud
For St. Cloud…a 30% chance of minor flooding, just above historical average.
Near average chance of moderate flooding (12%).
Flood Outlook – Mississippi at St. Paul
For St. Paul…historically average chance of minor flooding, about 30 percent.
Flood Outlook – Minnesota at Mankato
Less than 5 percent chance of flooding, well below average
Flood Outlook – St. Croix at Stillwater
For Stillwater… about a 60 percent chance of reaching flood stage, well above the
25 percent average. About a 40 percent chance of reaching moderate flood
level, 20 percent chance of hitting major flood level.
Flood Outlook – Eau Claire River
at Fall Creek
For the Eau Claire… about a 45 percent chance of reaching flood stage, above
the 25 percent average. About a 20 percent chance of reaching moderate flood
level, just above average.
Flood Outlook – Chippewa River at
Durand WI
For the Chippewa (WI)… about a 75 percent chance of reaching flood stage,
above the 45 percent average. About a 30 percent chance of reaching moderate
flood level, above the 15 percent historical normal.
Threat Factors
Main things to watch for that would increase flood threat…
 Extended period of well above normal temperatures (60s, for
instance), staying above freezing at night
 Moist air melts snow much faster than dry air, so look for
dewpoints well above freezing when the air is warm
 Any major rain or snow event that adds a significant amount of
water to wet snow (2 inches of water or more)
Things to watch for that keep the flood threat manageable…
 Temps in the 30s and 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.
So, with that said…what’s the forecast?
Weather Outlook
Short term forecast – through the next week
Melting over the weekend, then cooler again. Another storm on the horizon early
next week. Potential significant snow north of the Twin Cities
Weather Outlook
Seven Day Precipitation forecast
One to two inches of liquid possible over much of the area by the end of the week;
snowpack will increase again over northern/central MN and northern WI
Weather Outlook
8–14 Days – April 4 through 10
 Temperatures: below normal trend continues through at least
early April
Weather Outlook
8–14 Days – April 4 through 10
 Precipitation: equal chances of above, below, or normal
Weather Outlook
30 days – April
Temps: Cool
trend expected
to continue thru
April
Precipitation
(not shown):
no clear
indication
Weather Outlook
90 days – April through June
Temps: Cool
trend expected
to continue thru
April, then
moderate
Precipitation
(not shown):
no clear
indication
Weather forecast effect on flood
threat
Next week’s storm could be crucial…pay close attention to
forecasts on precipitation amounts next week. Likely to
add to the snowpack to the northern MN and WI basins,
further priming the threat for later in the spring. It could
enhance short term runoff around the Twin Cities and in
central WI.
After that…temperatures remain cool, melting slows again.
This could be a beneficial trend to reduce flood threat.
Our flood threat is becoming more susceptible to late spring
rains, as peak runoff will be later than normal. Stay tuned…
NOTE:
RFC daily forecasts will start in early April; some maybe by
this weekend if forecasts show significant rises.
For the Dreamers…
10 month forecast – Dec/Jan/Feb next winter
Yeah, we can dream…
More Info?
How to reach us…
*Webpages
Weather info: www.weather.gov/twincities
River info: http://water.weather.gov/ahps2/index.php?wfo=mpx
Text version of this outlook:
http://forecast.weather.gov/product.php?site=NWS&product=ESF&issued
by=MSP
•
More Info?
How to reach us…
*Facebook:
US National Weather Service Twin Cities
*Twitter:
@NWSTwinCities
*Contact:
- Craig Schmidt, Service Hydrologist, at
[email protected] / 952-368-2542
- NWS Chanhassen Operations at 952-361-6671