Four weeks after an early frost nipped scattered sections of Southwest Minnesota, a more general frost and freeze ended the growing season across the area on the mornings of October 10th and 11th. Though all reporting stations fell below 32 degrees, the coldest temperatures included 24 degrees at Granite Falls on Friday the 10th, and Saturday morning lows of 27 at Redwood Falls, Windom, and Slayton. These dates are very close to the normal time of our first hard freeze (28 degrees or colder) in the autumn.
Though October has started cooler than normal across the area (see map to left from the High Plains Regional Climate Center), the tendency for temperatures to fluctuate between well above and well below normal may very well repeat during the middle portion of October. Enjoy the next five mild days which should reach the low to middle 60s. Following some rain late Sunday and Sunday night (which should total less than 0.25″) excellent harvesting weather is likely for the remaining days through October 18th, helping to reduce the moisture content of standing corn.
This month is on track to join the cool and dry Octobers of 1987, 1991, and 2006 as years when El Nino events started which brought this type of October pattern . And yes, the Climate Prediction Center experts continue to forecast a 65% or higher probability that El Nino will finally take hold in the Pacific Ocean during the next few weeks.
Mid-September Historical Weather Highlights for Minnesota (from Twin Cities National Weather Service)
2002: A late-season tornado strikes Albertville just after midnight. It completely tore the roof off of one home. Roofs were partially off a number of other homes, many attached garages collapsed, and a couple of houses were rotated on their foundation. About 20 homes were damaged, nine of which sustained significant damage.
1986: 3 inch hail fell in Watonwan County.
1910: Duluth had the shortest growing season ever with frost free days from June 14 to September 10 (87days). Normally the frost-free season is 143 days.
1982: Two tornadoes touched down in Benton County. The F2 tornado caused $250,000 worth of damaged and the F0 caused $25,000.
1911: Pipestone is hit with baseball-sized hail that smashes numerous windows at the Calumet Hotel and high school. The local observer measured hail three inches deep. People got their photos taken in automobiles surrounded by the icy white ground.
1998: 1 to 1 3/4 inch hail fell in Meeker, Wright, Todd, and Wilkin Counties winds were also estimated over 50kts.
1980: Golfball to baseball sized hail hit St. Paul. One company had 75 to 95 percent of the glass in their greenhouses smashed.
If we look ahead a few weeks, there is a notable trend away from summer and toward winter. In October, our area is rapidly transitioning from the warm season to the cold season. Many more of the notable weather events from years past include well below freezing temperatures and early season snowfalls, with progressively fewer occurrences of heat waves or severe thunderstorms.
While the normal average highs for the month of October are close to 60 degrees across southern Minnesota, these normals plunge from the pleasant mid to upper 60s during the first few days of October to just above 50 degrees by month’s end. (Map provided by National Weather Service)
Some mid-October Historical Weather Highlights for Minnesota (from Twin Cities National Weather Service)
1937: Snowstorm leaves 10 inches at Bird Island.
1880: Earliest blizzard in Minnesota. Struck western Minnesota and the eastern Dakotas especially hard. Over a foot of snow in western counties. Railroads were blocked. Damage done to Great Lakes shipping. Huge drifts exceeding 20 ft formed in the Canby area lasted until the next spring when flooding occurred across the Minnesota River Valley.
1952: Record lows were reported across central Minnesota with lows from 10 to 15 degrees, including a low of 10 degrees at St. Cloud, 12 degrees at Glenwood, and 14 degrees at Alexandria, Litchfield, and Mora.
1950: Record high temperatures were set across the area as highs reached the mid to upper 80s. Minneapolis and Farmington saw highs of 87 degrees Fahrenheit, while Albert Lea reached 86 degrees.
1972: Cold Snap. 1 above in Tower. 9 in St Peter and Luverne.
1916: Redwood Falls received a record-setting 7 inches of snow.
1916: Snow fell in south central Minnesota with 4.5 inches recorded in New Ulm, 4 inches in Farmington and Hutchinson, 3.5 inches in Montevideo, and 3 inches in Faribault.
Fall and Winter Outlook
One of our reliable long-range forecast models is predicting a ridge of high pressure aloft to set up farther east than last winter, when it was situated off the U.S. West Coast. An upper-level ridge of high pressure as forecast over the inland western United States would be associated with above-average winter temperatures especially over western Canada, and below-average temperatures across the south-central and southeastern U.S. While October and November temperatures in Minnesota haven’t shown a strong trend with this upper-air pattern, mid-winter temperatures have tended to be milder than normal across the northern Plains of the U.S, including most of Minnesota.
The precipitation pattern is not well-defined with the predicted pattern, but the expected development of El Nino for the winter offers what I hope are some reliable clues for predicting the winter pattern. Of the most recent five winters having the weather pattern expected over the next five months combined with an El Nino event, three landed in the top 20 wettest of the past 120 years. Three of those five winters also ended up among the top 20 warmest since 1895, and neither of the other two winters was colder than normal. Because of these historical pieces of evidence, I have moderate confidence in predicting a near to warmer than normal winter, which is likely to bring MORE snow than last winter to Southwest Minnesota. Last winter’s extreme cold made it easy to overlook that it was the driest winter in Southwest Minnesota since 2007-08, even while east-central Minnesota including the Twin Cities area by contrast had its wettest winter since 2010-11. I would not expect eastern Minnesota to be snowier than last winter, but that area could very well see above normal snowfall again in 2014-15.
Month-by-Month Outlook through February:
October: Average highs fall from the upper 60s to near 50 by month’s end; average lows begin the month in the lower 40s and fall to near 30 by October 31st. Precipitation averages about 1.75” for Southwest Minnesota. Four of the past eight Octobers have been wetter than normal in Southwest Minnesota but individual years have shown some wild swings. Octobers of 2007 through 2009 were all among the 10 wettest in the past 120 years. Then we saw a string of three drier than normal Octobers which was snapped in 2013. There is about a 60% chance that October will end up drier than normal following some unsettled weather in the first couple weeks. The past two Octobers were a little cooler than normal, and there is about a 75% chance of this October being near to chillier than normal.
November: Average highs fall to just above the freezing mark by month’s end; average lows begin the month near 30 degrees but fall to the middle teens. Average precipitation runs about 1.25” for Southwest Minnesota . This month has been remarkably consistent for warmth and dryness during the past decade. November across Southwest Minnesota has averaged drier than normal for eight consecutive years, and last November broke a string of 9 consecutive mild Novembers. Temperatures in those nine mild Novembers (2004 to 2012) averaged 4.3 degrees above the long-term average! Of the next five months, this appears to be the one with the most uncertain outlook – in large measure because it’s a time of transition to milder conditions if El Nino takes hold of the winter weather pattern. Though it’s not as likely as October to be colder than normal, mild November weather is just slightly favored over chillier weather this year. The precipitation pattern could also go either way (call that a “toss-up”).
December: Temperatures continue to decline toward the winter lows, and by year end the average high is in the middle 20s with average lows near 5 above. Average precipitation declines to only about 0.70” for Southwest Minnesota. If it has seemed in recent years that winter really hits shortly after Thanksgiving, it may be due to the fact that eight of the past nine Decembers have been wetter (usually also whiter) than normal in Southwest Minnesota, with 2011 bringing the lone drier December in that time span. Last December was the 16th coldest on record and the coldest since 2000. This is the month with the strongest probability of being milder than normal, and drier than normal weather is also slightly favored. Only when El Nino was much stronger than expected this winter were both November and December consistently wet across Southwest Minnesota.
January: The average high hovers in the middle 20s and average lows near 5 above until both begin to rise slightly at month’s end. Average precipitation is only about 0.60” for Southwest Minnesota. 11 of the past 13 Januaries (with the exceptions being in 2010 and 2011) have been near normal or drier than normal in Southwest Minnesota. While colder than normal in 2014, January was no colder than February of 2014 and was not quite as cold as the chilly Januaries of 2009, 2010, or 2011. This was probably due to the limited snowfall last January.
February: Average temperatures recover with highs just above 32 and lows in the low to middle 10s by month’s end. Precipitation averages about 0.70” for Southwest Minnesota. In 2014, this was a dry month averaging about two-thirds of the normal precipitation across the area. This snapped a five-year string of near to wetter than normal Februaries. It was the coldest February since 1989, and the 13th coldest in the past 120 years. Taken together, the first two months of 2015 should have a two in three chance of being warmer than normal, and are nearly as likely (60% chance) to be wetter (and probably snowier) than normal. However, the expected milder temperatures would result in some of the moisture falling as mixed precipitation or possibly even some rain.
In a complete turnaround from June, the “wet” areas of Minnesota have been few and far between so far in July. Most of Southwest MN has averaged near 25% of the normal rainfall (or about 1.50 inches below normal) through Saturday the 19th. Soil moisture has now declined to the point that, unless rain falls very soon, prospects will be deteriorating for some crops.
The week ending July 19th averaged about 8 degrees cooler than normal, bringing monthly departures to between three and five degrees below normal across Southwest MN. The return of cooler than normal temperatures expected for the final weekend of July virtually guarantees our coolest July since 2009.
Though not as dry across the entire area as last week, all areas fell short of weekly normals during the July 7th to 13th time frame. Cool weather will see us through this week without stressing developing crops too much, but we will really need some better rain as temperatures climb to near and above normal levels by July 20th and beyond.
Posted Friday, June 6th —
Last Thursday, June 5th was an occasion when rainfall vastly exceeded forecasted amounts. Thursday was particularly unique in that unexpectedly heavy rainfall affected the area not once but twice in the same day! The morning rains developed in an atypical manner (more on that later), while rain had not been expected until much closer to mid-day. In general, there are several possible causes of summer rains being more or less abundant than forecast. Any or all of these can produce inaccurate forecasts of rainfall amounts.
- Warm season rain events have more moisture to draw upon, and may be concentrated in small cells or pockets of intense rainfall. This can produce an “all or nothing” type effect in which there can be a fine line between heavy rain and mere sprinkles, both in time and distance.
- Formation of storms may occur at the boundary of warm, humid air and cooler “outflow” remaining from earlier storms. These boundaries are often either undetected or handled poorly by the major forecast models. This effect definitely enhanced the strength of Thursday’s late afternoon thunderstorms.
- Forecaster experience may not help overcome the lack of help from the forecast models, because a weather pattern which usually produces little to no rain may produce heavy rain in a small fraction of events.
Specifically, I have identified a handful of reasons that Thursday’s rains were unusual.
- TIMING – Overnight storms typically die out around sunrise. These storms developed just after sunrise.
- SHORT-TERM MODELS had forecast the morning rains to stay to the north of the area.
- OTHER STORMS were occurring at the same time over Arkansas and Missouri. These often would have limited the moisture inflow needed to support heavy rainfall in southwest MN.
- UPPER-LEVEL SUPPORT for the storms was weakening during the day.
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