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



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

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

June Temperatures

June temperatures were close to average.  The average high was 77.5 degrees which is 0.1 degree above the three-decade mean.  The average low was 56.8 degrees which is 1.9 degrees above the three-decade mean.  This continues the trend observed over recent years of having the low temperatures warmer than the high temperatures, relative to the long term average.  This is another representation of our local climate being wetter than in the past.  The increase in rainfall leads to higher humidity and more clouds, all of which has a bigger impact on temperatures at night and less of an impact in the daytime.  The increase in average humidity also leads to fewer really hot days.  June had two days with highs in the 60s, 15 with highs in the 70s, and thirteen with highs in the 80s.  The warmest day last month was 89 on June 21. The coolest day was 66 degrees on June 6.  June had 12 mornings with lows in the 60s, 15 with lows in the 50s, and three with lows in the 40s. The coldest temperature was 44 degrees on June 8.  The warmest night was 69 degrees on June 27.   Meteorologist John Wheeler

June Wet and Stormy, Kind Of

June was a wet and stormy month.  Rivers are high from Manitoba to Tennessee.  Almost every evening on the national news there is coverage about all the severe storms this summer.  But the national tornado count on the Storm Prediction Center’s Annual Storm Summary web page shows that the last year to have had so few tornadoes through July 1 was 2005.  What about all the rain?  It has been wet but nowhere nearly as wet as it was in 1993.  June was a bad month in the Great Plains and Midwest for storms.  But June was certainly not record bad and it wasn’t really even unusually bad.   Instead, network news is just covering the heck out of stormy weather.  It is riveting and extremely popular.  Weather is good for ratings.  And while the coverage is well-intended and truthful, the viewers should not be persuaded by the sheer volume of storm coverage into thinking this summer is out of the ordinary.   Meteorologist John Wheeler

I Knew It Was Cold Here

An article last week in Nature Climate Change identified the few places around the Northern Hemisphere most prone to extreme weather.  Specifically, the study identified those places most likely to have stalled out large-scale jet stream waves as these are the mechanisms for too much rain, snow, cold, heat, etc.  For cold air anomalies, we are in a bad spot.  It turns out, the eastern half of North America is most vulnerable to long-term cold air outbreaks.  The worst flooding occurs in western Asia.  Drought is most prevalent across central North America, Europe, and central Asia.  Heat waves are most likely over western North America and central Asia.   Meteorologist John Wheeler

Daytime and Nighttime Storms

There are two times of day when thunderstorms are most likely to happen over eastern North Dakota and western Minnesota, and they are related to two distinctly different weather patterns.  During spring, early summer, and early fall, the most likely time for thunderstorms is in the late afternoon and early evening.  Near the hottest time of the day, thermals rising off the warm grounds are at their strongest and this may be just enough to kick off a few thunderstorms.  During July and August, we tend to get more thunderstorms after midnight.  When our weather is at its hottest, the upper levels of the atmosphere are often warm as well, making it harder for just the thermals to initiate storms.  But at night, here in the Northern Plains, storms can get a little boost from something called the Nocturnal Jet Stream; a river of air a few hundred feet above the ground which blows from south to north causing a convergence of air which enhances rising motions in the atmosphere.  Of course, it is possible for a thunderstorm to happen at any time of day.  But suppertime and after midnight are the most common times in our region.   Meteorologist John Wheeler