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Extension > Mark Seeley's WeatherTalk > Great Variation in Rainfall this Month

Friday, July 14, 2017

Great Variation in Rainfall this Month

Great Variation in Rainfall this Month:


So far this month the rains across the state have been very widely scattered and highly variable in amounts, including those of this week. This is especially true in western and southern counties. Across Otter Tail County total rainfall in July varies from less than a third of an inch to well over 2 inches; and across Blue Earth County rainfall for the month varies from less than a half inch to nearly 3.5 inches. Overall rainfall totals through the first 14 days of the month ranged from just trace amounts in portions of southwestern to nearly 3.5 inches in south-central Minnesota. Severe thunderstorms on Sunday, July 9th brought hail and high winds to many areas. Some very large hail (over 2 inch diameter) were reported, along with a tornado near Lake Crystal (Blue Earth County). Then another severe weather episode with dew points in the 70s F occurred across portions of central Minnesota over July 11-12, bringing hail and high winds to many areas. There was also a report of a tornado near Forest Lake. At one point, Xcel Energy reported over 56,000 customers without power because of high winds. The Minnesota State Climatology Office features more detailed descriptions of all of these storms so far this month.

Following the warm and sultry weather which produced the thunderstorms a cold front brought morning lows in the 40s and 50s F on July 13th. Crane Lake dropped all the way down to 37 degrees F on July 14th. This is a typical Minnesota rollercoaster pattern on the thermometer readings.

Weather Potpourri:


NOAA scientists announced this week, that after a number of years with little or no rise in global methane (a powerful greenhouse gas), there is now a rising trend in global methane that has been evident in the data every year since 2007. This trend had been predicted to resume by global climate models.

Hurricane Fernanda, located many hundreds of miles southwest of Baja California is expected to intensify and perhaps become a Saffir Simpson Category 4 storm (winds 130-150 mph) over the weekend and early next week. But it will remain well out to sea in the Eastern Pacific Ocean and no threat to land.

Earlier this week an iceberg the size of the state of Delaware broke away from the West Antarctica Ice Shelf (called Larson C) and is now floating. This 2200 square mile iceberg, estimated to weigh over a trillion tons, is expected to occasional get stuck on the bottom of the Wendell Sea over the next months and years. The weekly Earth & Space Science News from AGU provides more detail and perspective on this topic.

MPR listener question:


When I listen to the weather forecast I get confused by the rainfall predictions when meteorologists use the terms isolated showers, widely scattered showers, scattered showers, and widespread showers. Can you explain the differences?

Answer:


This jargon issue has been written about over the years by many meteorologists, and there are certainly some geographic disparities in what these terms imply. For our region of the country they generally mean the following:

Isolated showers implies less than a 25 percent chance of occurrence anywhere in the forecast area.
Widely scattered showers implies a 30-40 percent chance.
Scattered showers implies a 40-60 percent chance.
Widespread showers implies over a 60 percent chance.
The bottom line is that when the terms isolated or widely are used, it is more likely to remain dry where you are located.

Twin Cities Almanac for July 14th:


The average MSP high temperature for this date is 84 degrees F (plus or minus 7 degrees F standard deviation), while the average low is 65 degrees F (plus or minus 6 degrees F standard deviation).

MSP Local Records for July 14th:

MSP records for this date include: highest daily maximum temperature of 108 degrees F in 1936; lowest daily maximum temperature of 65 degrees F in 2014; lowest daily minimum temperature of 50 degrees F in 1930; highest daily minimum temperature of 79 degrees F in 1980; record precipitation of 3.17 inches in 1915. No snowfall has occurred on this date.

Average dew point for July 14th is 60 degrees F; the maximum dew point on this date is 76F in 1995; and the minimum dew point on this date is 40F in 1930.

All-time state records for July 14th:


The all-time state high temperature for today's date is 111 degrees F at New Ulm (Brown County) in 1936; the all-time state low for today's date is 30 degrees F at Alborn (St Louis County) in 1930. The all-time state record precipitation for this date is 5.49 inches at Carlos (Douglas County) in 2011. No snow has fallen on this date.

Past Weather Features:

Perhaps the coldest July 14 in state history came in 1930. At least 15 climate stations reported a morning low in the 30s F, and a few northern communities reported frost. The air was especially dry with humidity reported between 20 and 30 percent. For some northeastern climate stations the afternoon temperatures remained in the 60s F.

July 14, 1936 was the hottest in history with 50 Minnesota communities reporting an afternoon high temperature of 100 degrees F or greater. Overnight lows never cooled off close to normal and remained between 74 and 78 degrees F in most places. Many people slept outside or on their porches.

Strong thunderstorms passed over northern Minnesota July 14-15, 1937 delivering hail along with 3 to 6 inches of rainfall to many areas, including Baudette. In Baudette ended up with 12.50 inches for the month, recording the wettest July in history there.

Eight consecutive days with rain showers saturated southern Minnesota over July 9-16, 2011. Many climate stations reported 5 to 8 inches of rain over that period and some corn and soybean fields showed standing water.

Outlook:

Warm and humid on Saturday, with a slight chance of thunderstorms. Cooler on Sunday with temperatures falling back closer to normal. Temperatures warming again Monday and Tuesday to slightly above normal, with chances for showers and thunderstorms much of next week.














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