Posted at 8:48 AM on October 1, 2012
by Paul Huttner
82F & 77F for highs in the metro last weekend
+1.9F temps vs. average at MSP in September
16th straight month above average in MInnesota
70s linger through Wednesday in southern MN & the metro
Cold front - season's coldest air mass sails south by Thursday
Accumulating snow potential by Thursday AM up north
Season's 1st metro frost likely by Saturday AM
Sibieran snow cover running below average - what it may mean for Minnesota this winter
High fire danger in western Minnesota again
Roller Coaster week ahead:
Get ready for another ride on the Minnesota Roller Coaster.
September warmth lingers into the 1st 3 days of October this week. Highs will push 70 in the metro and southern Minnesota today and 70s will linger Tuesday & Wednesday. There may be just enough sun & southerly air flow to boost temps to the upper 70 to near 80F in some spots by Wednesday.
October may have arrived on the calendar, but thermometers won't show it through mid week.
Season' coldest air mass oozes south:
Our next Canadian import sails south Thursday as the season's coldest air mass pushes south.
Low pressure will spin through northern Minnesota Wednesday night. Behind the low, sub freezing air will slide south. There should be enough moisture...and enough cold air to produce the first (heavy?) accumulating snow north & west of a Grand Forks to Ely line by Thursday morning.
A huge bubble of frosty high pressure sends temps plummeting by Friday. 30s will return to the metro by Friday morning, and the season's 1st frost/freeze in the "inner core" of the metro appears to be a lock by Saturday morning. Right now I am forecasting temps near 30F at MSP Airport Saturday morning, with 20s in the suburbs.
Siberian snow cover running below average:
As we begin to piece together the winter outlook from the weather lab this month, one early trend is for below average snow cover in Siberia so far this fall.
Recent studies seem to show a link between extensive Siberian snow cover in fall and cold air outbreaks in winter in the USA. A cold snow covered Siberia may kink the jet stream and send pulses of arctic air south into the USA.
Last winter you may recall I reported that Siberian snow cover was running well below average, and suggested it may not be a severe winter like many were projecting.
So far this fall, Siberian snow cover may favor a warm bias again this winter.
There are a lot of climatological "plates spinning in the air" now when it comes to our winter outlook. A (slowly) developing El Nino, PDO & AO phases, the lowest Arctic Sea ice on record and Siberian snow cover are just a few. All of these variables are running against the background hum of decadal climate changes that tend to produce warmer outcomes in winter at high latitudes.
You may recall last October I saw trends that lead me to the conclusion that the winter was likely to show wild swings, and be milder than many were forecasting. It turned out I was too conservative on the magnitude of the mild signals.
Heres' an excerpt from my winter outlook last October.
(In retrospect, I should have made this the headline!)
Decadal Trends: Our changing winter climate?
Juxtaposed over the technical and dynamic factors that may control winter weather are so called decadal trends, which lean strongly in favor of milder winters with less snowfall for Minnesota.
Some facts from the past decade include:
-7 of the past 10 winters have featured significantly below average snowfall in the metro, (70% bias toward less than average snow in the past 10 years)
-In those years the average winter snowfall has been 33.6"
(Roughly 22" below the 30 year average of 55.9"!)
-6 of the past 10 winters have featured above average temperatures
(60% bias toward milder than average winters the past 10 years)
-Minnesota winter nights got a lot milder in the past 30 years! (1981-2010 data set) Overnight low (minimum) temperatures in January average a full 2 to 4 degrees F warmer than the previous 30 year (1971-2000) data set.
Variable: Decadal trends in winter temps and snowfall in Minnesota
Potential effect on Minnesota winter: Milder winters temps (especially at night) and a apparent bias toward lower winter snowfall totals.
Trend for 2011-'12: Increased odds for a milder winter with less snow than 2010-'11.
Rather than giving you a "moving target" outlook every few days or weeks, I'll issue an outlook, stick with it and be accountable for the outcome.
Stay tuned in the next few weeks as we try and nail down a winter forecast that has some "predictive value."
2003 the last time White Bear Lake was at "ordinary high water level" of 923.42 feet above sea level
5+ foot drop in lake level from "normal" level since 2003
2" White Bear Lake is within about 2" of all time record low reached in November 2010
86F water temperature in White Bear lake on July 17th of this year
Has 25% of the water volume of White Bear Lake "disappeared" since 2003?
White Bear: Incredible shrinking lake:
These are difficult days for people who swim in White Bear Lake's usually cool waters and call it's receding shoreline home. Plummeting water levels on White Bear may be part local geography, and part of a bigger trend on Minnesota's 10,000+ lakes.
White Bear Lake has always had big fluctuations in lake levels.
But the sustained drop in the water levels in excess of 5 feet on White Bear since 2003 may be a harbinger of things to come for Minnesota's Land of 10,000 lakes.
The plunge in water levels of White Bear and other Minnesota lakes, marshes and ponds mimic a shift to a warmer climate regime in Minnesota in the past decade.
White Bear's unique geography and hydrology make it extra sensitive to changes in precipitation and increased evaporation rates associated with a warmer climate.
-White Bear's relatively small watershed makes it especially vulnerable to reduced winter snowfall and the spring runoff that feeds the lake. With less area for runoff into the lake, it takes more rain and snow to boost water levels in White Bear.
-Longer "ice free" seasons (by 2 to 4 weeks or more) open the lake surface to increased evaporation in spring and fall.
-Hotter summers, and warmer, longer spring and fall ice free periods each year mean more water is sucked form the surface of Minnesota's lakes than in decades past.
Increased evaporation makes our lakes increasingly vulnerable to any reduction in annual rain or snowfall.
Increased Groundwater Pumping: Draining White Bear from below?
A very timely and in depth piece from The Freshwater Society highlights the threat to White Bear's water level from increased groundwater pumping below the lake.
Here are some excerptsfrom the Freshwater report.
From mid-2003 to the present, White Bear's water level dropped more than 5 feet. In late 2010, concern about the drop among citizens and officials in communities around the lake led to a $200,000 research project conducted by the U.S. Geological Survey with assistance from the state Department of Natural Resources, the Pollution Control Agency, the Board of Water and Soil Resources and the Metropolitan Council.
The research, funded by the USGS, the state and a number of local governmental units, reinforced some old theories and produced some new evidence about the causes of the lake's decline.
The findings so far:
-White Bear drains a very small watershed and has always had big decreases in area and volume during extended dry periods when rainfall and melting snow do not keep up with evaporation.
-Chemical testing of water from wells around the lakes confirms that lake water is flowing out the bottom of the lake into groundwater aquifers that feed those wells.
-Pumping from high-capacity wells in suburban communities that mostly draw their water from those aquifers more than doubled over the last 30 years.
There are varying scientific opinions, but some believe as much as 25% of White Bear's water volume may have been lost from below due to increased groundwater pumping in the aquifer below the lake.
A regression model simulated the impact on water levels of the precipitation decline and the increased pumping. The pumping accounted for nearly four and a half feet of the water level decline between 2003 and 2011, according to the simulation. That four-and-a-half-foot difference across the lake equals a staggering 4.8 billion gallons - a loss of more than a quarter of the lake's previous volume.
Not everyone buys the notion that groundwater pumping around the lake has had that big an impact. "I accept that the added pressure from that municipal pumping on that aquifer had an effect," said Luke Michaud, the vice chair of the White Bear Lake Conservation District. "I'm skeptical of that four feet."
White Bear Lake: Canary in a Minnesota climate change coal mine?
As drought deepens and climate shifts in Minnesota a bigger question looms.
-Is a smaller White Bear Lake unique, or part of a larger trend of "shrinking" Minnesota lakes?
White Bear is not the only Minnesota lake that's receding these days. Take a close look at ponds and marshes in your neighborhood that are drying up. Other lakes are showing the stress of deepening drought through lower water levels.
The water level in Lake Minnetonka has dropped nearly 17" (16.8") since June 22nd.
Even mighty Lake Superior is down well below the mean lake level for early October, and trending downward toward record low observed water level.
Water levels in some lakes like Gull and Minnetonka are managed by dams. Managed lakes are less vulnerable, but not totally immune to falling water levels from a shifting climate and increased groundwater pumping.
There is little doubt that the documented shift to a warmer and longer "ice free" climate with warmer spring and fall periods in Minnesota will expose our 10.000+ lakes to increased surface water loss through evaporation.
Combine that with hotter summers like 2012, increased drought, less winter snowfall and subsequent spring snow melt runoff to boost lake levels in spring and you create a scenario that puts a high degree of stress on Minnesota lake levels.
White Bear Lake may be unique. It may also be trying to tell us something about the future of our Land of 10,000 Lakes.