Winter weather recap and long range forecast
The past winter has been cooler and drier than normal. La Nina will continue to impact conditions for early spring.
The winter of 2010-11 will go into the books as cooler and drier than normal across most of Michigan, although there were some regional differences across the state. Mean temperatures for the December through February ranged from 1.0 degree Fahrenheit above normal across western and central sections of Upper Michigan to more than 4 degrees below normal in southeastern Lower Michigan. For the state as a whole, it was the 35th coldest such period on record over 116 years.
Precipitation ranged from close to normal across extreme southern and western sections of the state to less than 50 percent of normal over northeastern sections. Averaged across the entire state, it was the 21st driest of 116 winters on record. While a strong La Nina event developed across the equatorial Pacific region last fall, the observed conditions here in Michigan were drier than is typically the case in La Nina events. In contrast, wetter than normal conditions were recorded in areas to our west, across the Upper Mississippi Valley and northern Great Plains states.
With the exception of a brief period just before New Year’s Day (which resulted in a major thaw across the state), persistent northwesterly upper air flow brought colder and drier weather to the Great Lakes region for much of December, January, and early February. A major change in the jet stream pattern across North America took place near the end of the second week of February, with the replacement of the very persistent troughing pattern that had been locked across eastern sections of the continent with broad ridging. This change brought southwesterly flow back to the Great Lakes region along with a series of relatively mild Pacific-origin air masses and an extended thaw that has melted away much or all of the heavy snowpack that had built up across the state. Given that soil temperatures generally remained just above freezing during the coldest part of the winter below the insulation provided by the snow pack, much of the melt water has infiltrated back into the soil profile as recharge.
In recent weeks, an upper air troughing feature across western sections of the United States (much more typical of La Nina events) has resulted in relatively mild and wet conditions across much of the Midwest, The result has been a very active storm track through the region and the passage of a series of low pressure systems. Given the drier than normal conditions through much of the winter, the latest issue of the U.S. Drought Monitor still categorizes portions of Upper and northern Lower Michigan and areas just to the south of Michigan in northern Indiana and Ohio as abnormally dry. However, recent wetter weather and the forecast of more in the near future suggest than this classification will likely be temporary.
So how long will the active weather pattern across the region last? The best guess is probably several more weeks at least. The current upper air pattern is typical of La Nina episodes, and is forecast to generally remain in place through much of the upcoming spring, with an enhanced storm track across the Ohio Valley region to our south. While there may be temporary breaks in this pattern, this would mean temperatures averaging close to normal in most areas of the state with above normal precipitation totals, including at least some late season snowfall. This would also include northern sections of the state missed by much of the recent wet weather systems.
Latest medium range forecast guidance calls for upper air troughs just off the western coast of the country and just to the east of New England, with broad zonal, west-to-east flow across much of the Midwest. The latest NOAA Climate Prediction Center 6-10 day and 8-14 day outlooks (March 22-26 and March 26-30) both call for mean temperatures across Michigan to range from near normal levels across southwestern portions of the state to below normal levels across the northeast. Above normal precipitation totals are a good bet for both periods. Normal high and low temperatures during late March range from the low 40’s and mid 20’s across far northern sections of the state to the low 50’s and mid 30’s across the south. Normal weekly precipitation totals for late March range from less than 0.4” across western Upper Michigan to more than 0.65” across the southern Lower Peninsula.
Further ahead, the Climate Prediction Center outlook for March through May calls for near normal mean temperatures across all but far northwestern sections of the state, where below normal levels are projected. Precipitation totals are expected to remain in the equal chances category statewide. I personally think normal to above normal precipitation totals are a good bet at least through April, which would mean wet soils and potentially longer than normal fieldwork delays as the growing season approaches.
At this point, with the current La Nina event projected to dissipate during the next couple of months – there are already signs of this occurring in the equatorial Pacific – there is no real forecast direction on either temperatures or precipitation in Michigan or the Midwest for the upcoming summer.