Wet October

October 2008 will probably always be remembered for its abundant rainfall. Last month’s official total was 4.46 inches which ranked it as the fifth wettest October on record. Combined with the 5.08 inches that fell in September, 9.54 inches of rain has fallen so far this autumn season ranking this fall as the third wettest on record with an entire month to go.

The excessive rain caused flooding on area rivers and the Red crested at nearly 25.5 feet, an October record. Last month started mild, had a noticeable cool down toward the middle of the month, but the last several days were very mild which pushed the average temperature to 1.3 degrees above normal.

The warmest temperature was observed on October 2 when the temperature reached 74 degrees, that was also the only day of the month the temperature hit 70. The coldest morning was on October 28 when we woke up to a temperature of 24 degrees.

Wet and Dry

Since the middle of June, the precipitation contrasts across Minnesota has been striking. The southern third of Minnesota including the arrowhead region has been very dry. The Twin Cities area for example has had rainfall deficits of five to nine inches in the past five months and is currently in a moderate drought according to the Climate Prediction Center.

Whereas west central Minnesota, including Norman, Clay and Wilkin counties have had rainfall surpluses of four to eight inches during the same time period. A persistent storm track has been bringing numerous storms from Nebraska through South Dakota into our area consistently missing much of Minnesota.

Historically when the Pacific Ocean has been in its cold phase and the Atlantic Ocean is in its warm phase, western North Dakota and eastern Minnesota have a higher percent chance of drought, whereas our area tends to be a bit wetter. This year has been an extreme example of this pattern.

CoCo for Weather

CoCoRaHS is coming to North Dakota on November 1. Co-Co what? CoCoRaHS is an acronym for the Community Collaborative Rain, Hail and Snow Network. CoCoRaHS is a network of volunteers of all ages and backgrounds working together to measure and map precipitation (rain, hail and snow).

The network hopes to provide a dense network of precipitation data throughout the United States. These additional data will give meteorologists, hydrologist and researchers additional information on the evolution of storms and their impact on agriculture, hydrological systems and a host of other uses. The goal is to get 1000 volunteers in North Dakota to join the network.

Minnesota is currently one of the few states not participating in the program, but probably will in the near future. If you are interested in the weather and could like to volunteer, you can go to http://cocorahs.org for more information or be free to contact us at the email us at weather@wday.com.

Cold Pacific

The Pacific Ocean goes through long term phase changes from cold to warm waters approximately every thirty years. The reason for this is not understood. With the recent switch of the Pacific Ocean to a colder phase, many parts of the west coast of North America have recorded persistently cooler than average temperatures.

The area that has observed the most pronounced cool down has probably been southern Alaska. Anchorage saw a dramatic rise in average temperatures in the late 1970s when the Pacific switched into its warm phase, but with the recent shift to colder water, significantly cooler weather has been recorded. The summer of 2008 was the coldest summer in thirty years in southern Alaska, which just happens to be the last time the Pacific Ocean was in its cold phase.

For our area, more persistent La Ninas triggered by this cool phase in the Pacific will probably lead to colder winters becoming more common.

70-less

The latest seventy degree day ever recorded in Fargo Moorhead was on November 17, 1953, so you can never say never in our climate, but the odds are quite high that we have recorded our last seventy degree temperature for the season.

Our last seventy occurred back on October 2 when we recorded a high of 74 degrees. If that holds, it would be the earliest that milestone was last achieved since 1985. In the early to mid 1980s we had several years, including 1981, 1982, 1983, and the one in 1985 that our last seventy occurred in September.Back in 1985 our last seventy degree temperature was observed very early on September 18. Colder weather certainly came very early to the area that year.

The average last seventy degree day over the past 30 years as been around October 15, so unless the weather patterns change quickly (which is possible next week) we observed our last seventy a couple of weeks before the average this autumn.

Not Flat Enough

Although this area is not known for its topographical features, there is enough elevation for subtle weather differences. One common example is low spots in the surrounding landscape usually having frost first.

Temperatures can vary by several degrees as the colder, more dense air settles into the lowest terrain. But higher elevations also can have a strong effect on temperatures in this area. Dry air cools at a rate of 5.5 degrees Fahrenheit per thousand feet and eastern North Dakota and western Minnesota does have an elevation change of around 800 feet.

The most pronounced is in northeastern North Dakota. Langdon, ND for instance sits at an elevation of around 1600 feet, approximately 40 miles away; Park River’s elevation is 500 feet lower. Over that short distance Park River’s average first frost is about two weeks later than in Langdon, which translates into a three to four week longer growing season which can mostly be attributed to elevation.

Autumn Freeze

The most common question asked of me in recent days has been when do you think we will see our first hard freeze? A hard freeze by definition is a temperature of 28 degrees or lower. Fargo Moorhead’s average first hard freeze is October 4.

If you look back at the records it is amazing what a high percentage of years will observe a freeze during the first ten days of October, right near the average. Since records started in 1881 we have officially recorded our first freeze of autumn in November only five times. The most recent year this occurred was back in 1998, the others occurred in 1940, 1931, 1924 and 1921.

The record was set in 1931 when the first hard freeze held off until November 10. With the exception of 1924, all these years had very average first frost dates (32 degrees), but the really cold air held off until much later.

Top 10 Galore

In previous weather talks we have mentioned that September was the fifth wettest on record, October is already the ninth wettest and with several weeks to go this autumn is the eight wettest on record.

Over eight and one-half inches of rain has fallen since September 1 which has pushed our yearly rain total to 27 inches. It will only take another 1.5 inches of rain and/or melted snow to push 2008 into the top ten wettest on record. Average precipitation through the rest of the year would be approximately three inches, so the odds do favor this year ending in the top ten for rainfall.

I have been asked if this wet fall will lead to a snowy winter. Eight out of the ten wettest autumns had near normal or below normal snowfall the following winter, with one being the driest on record.  But the two exceptions were the winters of 1896-7 and 1996-7, two of the snowiest ever recorded.

First Frost

On Tuesday, October 14, the temperature at Hector International dropped to 31 degrees, officially ending the growing season in Fargo Moorhead. Our last frost of spring was very late, occurring on May 27, which was the latest since 1969.

Our average first frost of autumn is on September 24, so we were able to stretch the growing season by nearly three weeks beyond the average. So even with the late spring frost, the growing season for 2008 was 141 days, about one week longer than average. This was also the fifth straight year, and the ninth out of the last fifteen, with the first frost occurring in October.

These later than average frosts could be attributed to many factors, but these past 15 years have been generally wetter than average and moist soils do help keep the temperature up at night, plus the urban heat island around Fargo Moorhead is a factor as well.

 

Too Much

The first half of October of course has been very wet. So far we have had over 3.5 inches of rain with two full weeks of the month ahead of us. This month already ranks as the ninth wettest on record and it will take very little additional rainfall to move us up the list a few more spots.

If the rest of the month has near average rainfall we would receive about one more inch of rain. With both September and October being very wet months, our total for the autumn season is already more than 8.5 inches which places this autumn season in the top 10 wettest on record as well.

November averages around one inch of rain so if by chance we get average precipitation the next six weeks, this autumn would end up the wettest on record.