Wet or Dry?

Tuesday, August 5, 2014

July rainfall at the official Fargo Moorhead gauge at Hector International Airport was 1.69 inches.  This is 1.10 inches below the average of 2.79 inches.  So it was dry but not extremely dry.  And, of course, above average rainfall in June has carried us pretty well.  Amounts vary, of course, as is typical.  Grand Forks received 3.70 inches in July and that area is still very wet.  I got a call last week from a man who farms 30 miles west of Fargo who measured just 0.45 inches of rain in July.  He told me it was his driest July in 27 years of measuring.  This illustrates the random nature of summer precipitation.  Because thunderstorms can drop heavy rain in one spot and entirely miss another spot a few miles away, it becomes difficult to talk in general terms about it being wet or dry in summer.   Meteorologist John Wheeler

 

 

Late Summer Heat Wave

Do you remember the hullabaloo last year over whether or not schools should start up in mid to late August or wait until after Labor Day?  The discussion was initiated when eight of the last 13 days of August, 2013, were in the 90s; four of those days between 94 and 96 degrees.  The Fargo Public School District did rearrange this year’s schedule to start a week later than planned, on August 27.  The weather can still be hot in late August and even in September, but the likelihood of getting into the 90s is statistically much greater on the 20th of August than it is on the 27th.   Could we get a late summer heat wave again this year?  The pattern makes this less likely but not impossible.  Those 13 days at the end of August, 2013, were the hottest 13 days of the year.    Meteorologist John Wheeler

The American Monsoon

July and August is the time of the American Monsoon.  During June and early July, the desert areas from northern Mexico northward into the Rocky Mountain States heat up from day after day of sunny weather.  Temperatures reach well into the 100s at lower elevations, and sometimes into the 110s and 120s in parts of Arizona and California.  The hot air becomes less dense (with lower barometric pressure).  During July and August, air moves in from all around in response to the lower pressure, but mountain ranges block much of this movement except for a stream of tropical air from the eastern Pacific which comes by way of the Gulf of Baja.  The higher humidity in this air leads to frequent thunderstorm activity over the mountains of the Southwest.  Ironically, this is also the peak of the Southwestern fire season as some of the mountain storms produce lots of lightning and very little rain.   Meteorologist John Wheeler

Neither Hot Nor Cold Here

Hot weather has been hardly noticeable this summer.  Of the six 90 degree days so far in 2014, three came in May when humidity was low.  The other three 90 degree days all occurred in July and coincided with dew points in the 70s and so were undeniably hot and humid.  But there have been just three such days.  However, the lack of hot afternoons is not reflected in thel average temperature of the summer.  While this summer’s high temperatures have been running generally cooler than average, the summer’s low temperatures have been slightly above average.  Twice this past month, Fargo Moorhead has recorded high temperatures in the 60s.  Both were close to setting the daily record low maximum temperature record of the day.  However, we have not been close to any daily record low minimum temperatures this summer.    John Wheeler

Meanwhile, the Middle West, the Great Lakes, and the Mid-South regions have all been having a cooler than average summer.  On the other hand, it has been a hot summer throughout the American West.  Driving this pattern is a huge region of warmer than average sea surface temperatures across the northern and eastern Pacific.  You may have caught news of a rare summer lightning strike from a thunderstorm in Venice, California, earlier this week.  Warm ocean temperatures off the usually cool California coast helped create that storm. Because the Polar Jet Stream is formed above the region of greatest temperature contrast, the warm water in the North Pacific is keeping the Polar Jet further north over the Pacific and western North America but then it dives southward across the Northern Plains.  This is why the summer has been cool to our east and hot to our west.    Locally, we have tended to go back and forth from warm to cool with very little extreme heat.  This is all due to the placement of the Jet Stream which is due to the pool of warm water in the North Pacific.        Meteorologist John Wheeler

Wake Low Wind

On Thursday, July 24, an area of 50-60 mph winds developed over a large area south of Fargo Moorhead eastward across parts of Becker and Otter Tail counties.  The winds were especially problematic around Minnesota lakes, causing high waves to wash over shorelines.  The wind was caused by a condition known as a wake low.  Wake low winds sometimes form in the wake of a squall line.  The combination of adjacent areas of warm and and rain-cooled air creates a localized tight pressure field which makes it windy.  Wake low winds usually affect an area the size of two or three counties and last for one to three hours.  Winds of 40-60 mph are common but stronger winds are possible.  Wake low events defy National Weather Service storm warning products because they are not associated directly with the thunderstorms which cause them but are of too short a duration and too small in area for a high wind warning.  They happen most summers somewhere in our region but several years may pass between wake low winds at any one spot.  This makes them rare enough to be unfamiliar to the public as well.    Meteorologist John Wheeler.

Rain-Wrapped Tornado

The National Weather Service found evidence of a tornado within the widespread straight-line wind damage left behind after the Monday night storm.  The damage path is approximately 28 miles long through Polk and Red Lake counties and was discovered by the nature of the damage; debris was lifted higher and thrown further in a manner usually associated with tornadoes.  No one actually saw the tornado because it was entirely wrapped in heavy rain and was surrounded by a large area of very strong non-tornado wind.  A few people along did report hearing the “freight train roar” often associated with tornadoes, butthis sound can sometimes be heard in strong straight line wind storms as well.  Rain-wrapped tornadoes are not common in the northern Plains but are more common in the South where more humid environments often produce more widespread rain around tornadoes.  Rain-wrapped tornadoes are often difficult to detect except by Doppler radar, and the National Weather Service did have a tornado Warning in effect at the time.  This illustrates the need for people to take all Tornado Warnings seriously.  Fortunately, there were no injuries Monday night.

The tornado was a part of a huge thunderstorm complex which produced wind damage along a more than 500 mile path through North Dakota and Minnesota into northern Wisconsin and northern Michigan.  It began Monday afternoon and lasted into early Tuesday.  The storm complex, called a derecho, happens from time to time when hot and humid air in the lower atmosphere is topped by an upper air disturbance of higher winds and cooler temperatures.  The cool air aloft makes the air very unstable.  As the developing thunderstorms form into a line, some mechanism forces some of the stronger upper-level wind down to the ground. This condition can continue for hours, causing near-continuous wind damage.  In the Monday night storm, the mechanism responsible for forcing the wind was a small area of low pressure which formed over northeast North Dakota and then continued to move east with the storm.

By far, most of the wind damage Monday night was due to straight-line wind.  There were many reports of wind speeds estimated to be in the 60 to 80 mph range.  The tornado produced wind in this range as well, along with a few locations of 110-120 mph wind, all in Polk County near and southwest of Crookston.  The 110+ mph wind allow for the tornado to get an EF-2 rating.

Meteorologist John Wheeler

What Really Is the Record?

Fargo Moorhead weather data has been measured and recorded at Hector Airport since February of 1942.  Prior to that, our weather was recorded at the National Weather Bureau Office in Moorhead, in what is now the Rourke Museum.  But I recently learned from Daryl Ritchison of the North Dakota Climate Office that sporadic record keeping actually had begun at the Fargo Airport in 1930, and meticulous, hourly weather records from Hector started in 1932.  This means there is a period of ten years during the Dust Bowl when there is a complete other set of weather records for this area.  The Moorhead data are the numbers used for the official record because that was the official site until 1942.  But the Fargo data appear to be good data.  One item that stands out is July 6, 1936.  The all-time record high for Fargo Moorhead of 114 degrees was set that afternoon.  However, over in Fargo, the unofficial instrument at Hector recorded 115 degrees for two consecutive hours that day.    Meteorologist John Wheeler

The Worst Heat Wave

At this time in 1936, our region was in the about to begin its most extreme heat wave on record.  For eleven straight days, from July 6-16, the high temperature in Fargo Moorhead was at least 99 degrees.  The average high during the period was 104 degrees.  Nine of the eleven days were in the 100s.  The hottest temperature during the heat wave was the 114 reading on July 6 which is still the hottest on record for Fargo Moorhead.  There was little relief at night, either.  Most morning lows were in the 70s and two mornings, July 10 and 11, were 82 and 80 degrees.  The heat withered crops and tested the endurance of people.  Most rural areas still had no electricity so there was not even a fan to use.  The remainder of that summer was hot and dry and there was one more 100 degree day on September 21.  The ten days of 100 degree weather are the most recorded in Fargo Moorhead  in one year.     Meteorologist John Wheeler

Cold Winters, Cool Summers

From now through the middle of August is the hottest time of year in our region.  And that is not saying much.  The smoothed daily average high temperature is in in the 80s, peaking at 83 degrees for about three weeks from mid-July into August.  Even during our summer peak, any day is statistically more likely to be in the 70s than in the 90s.  We average 13 days a year of 90 degree temperatures.  On average, eleven of those days happen during July and August.  We only get to 100 degrees once every few years.  The last time was in 2012 and the last time before that was in 2006.  Before 1993, when it started raining more, 100 degree days were more common, but still happened less than once a year on average.  People say we live in a region of cold winters and hot summers.  They are right about the winters but our summers are generally quite cool.     Meteorologist John Wheeler

Where’s the Heat?

If you are as yet unsatisfied with our northern summer and require some real heat to get yourself into a summer frame of mind, may I recommend Las Vegas, Nevada or the surrounding desert of southern Nevada and California?  During June, 21 of the 30 days of the month were in the 100s, the hottest being 111 degrees June 30.  Nearby Needles, California, had just one day at 99 degrees and the other 29 were in the 100s.  At the weather station in Death Valley, the coolest day of the month was 103 and the hottest was 120 degrees.  Death Valley holds the record for the hottest properly measured (and officially recognized) temperature on Earth of 134 degrees set July 10, 1934.   Meteorologist John Wheeler