Were dew point & heat index records “agriculturally induced?”

It's a good thing the climate gurus at the MN State Climate Office are getting back to work soon. They have a lot of work to catch up on!

A slew of new weather records will need to be verified in the coming days and weeks.

Among them will be the apparent all time highest dew point and heat index on record Minnesota.

The dew point sensor at Moorhead spiked to 88 degrees at 7pm Tuesday evening. That's the highest dew point ever recorded in Minnesota. (Previous record was/is 86 degrees)

When you combine the air temperature of 93 at that hour, the heat index calculates out to a Persian Gulf level of 130 degrees! That would also be the highest heat index ever recorded in Minnesota. (Previously 124 degrees at Moorhead in 1966)

An interesting post from the Grand Forks NWS raises questions about whether the data will stand. It turns out the Moorhead AWOS station is surrounded by soybean & sugar beet fields. It's also over a bed of clover, and had standing water from heavy rainfall under/near the sensor.

From Grand Forks NWS:

Hottest Place On Earth?

"Was Moorhead Minnesota one of the Hottest Places on Earth Tuesday afternoon?

Based on data from the Moorhead Automated Weather Observing System (AWOS), there was a period of time when the dew-point temperature reached 88 degrees Fahrenheit! Values this high are usually reserved for locations such as the Mexican Gulf Coast, Saudi Arabia or other extremely hot and humid places. But, was the dew-point actually that high?

Going back and reviewing the data from the Moorhead Airport, it would appear at first blush the data is accurate. Accurate, but not representative. Verifying the data will take some time however. There are several reasons to question the precision of the dew-point sensor.

First: The AWOS is surrounded by Sugar Beets and Soy Beans - two of the most prodigious transpiring plants. Second, there was very heavy rainfall Tuesday morning across the region. This rain served to saturate the local soils and encourage plant growth. Plus, under the sensor is 4-6" high clover in flower (clover you would find in your yard, not the crop), with much ponding water within a few feet of the sensor as well. Third, when compared to the Automated Surface Observation System (ASOS) at Fargo's Hector Field the maximum dew-point was 5 degrees lower, peaking at 83 degrees Fahrenheit for one hour only. (Below is a table comparing the Fargo ASOS and Moorhead AWOS for part of the day)

In looking at the data from the surrounding stations, several of the North Dakota Agricultural Network Stations (NDAWN) had similar readings. At face value, this supports the Moorhead dew-point of 88F. However, the NDAWN stations are located in such a way as to measure the moisture of the crop canopy environment, not the atmosphere. So, on the one hand if the dew-point did hit 88 degrees Fahrenheit, resulting in a Heat Index of 130 degrees Fahrenheit, it was not because of true meteorological effects but because of an agricultural bias. This makes the information, relative to official climatic sources, less representative, and should be used with caution.

While it is possible the Moorhead dew-point did reach 88 degrees Fahrenheit, it did so because the weather station is located in an agricultural field surrounded by water, or very wet soils, and crops that release a great deal of water vapor into the atmosphere. The sensor while measuring the moisture of a very local place, did not represent the free atmosphere as a whole. There are very specific rules and regulations dictating the location of weather equipment, the type of vegetation and distance from agricultural crops

Whatever the cause, a 130F Heat Index would be intense. Is it accurate? It is impossible to determine the accuracy of Moorhead AWOS at this time, so that 130F Heat Index is questionable. Is it a record? That will take time to ascertain. We will be looking at the data and making a determination later.

Below is a table comparing the Fargo ASOS with the Moorhead AWOS during the hours of Noon through Midnight, Tuesday July 19 2011. During the period when the Moorhead AWOS was reporting an 88 degree dew-point, the Fargo ASOS was 5 to 9 degrees lower."

NWS comparison of readings in Fargo and Moorhead Tuesday. (Click to enlarge!)

Huttner's take on the data: (For what it's worth!)

My take on the facts and data here puts me in the camp that would uphold Tuesday's records.

Here's why:

-If row crops are in fact contributing to higher dew points as has been documented in the past, then most or all observing stations in Minnesota had higher "agriculturally modified" dew points Tuesday. (And on most summer days)

Why would you subtract out one site (Moorhead) when most other sites, and indeed the entire lower atmosphere over most of Minnesota has been "injected" with additional moisture from crop evapotranspiration?

-The crops near the Moorhead site would also tend to lower air temperatures at the site vs. a surrounding urban environment. If we adjusted the observed air temperature upward according to surrounding environmental factors the heat index would also have to be adjusted upward!

-If there was standing water from recent rainfall near the AWOS site (with additional evaporation into the lower atmosphere) that is a legitimate "naturally caused" factor. The Persian Gulf and Gulf of Mexico modify air masses with higher dew points, so do lakes and huge puddles (standing rainwater) in Minnesota!

-If the sensor is accurate, then 88 degrees was actually the dew point and 130 degrees the heat index at that location! If you're standing there, it felt like 130 degrees! Period.

If a farmer had standing rainwater in his fields Tuesday it would have felt the same way at that location...even if there was no weather sensor there to detect the readings. Simply put, those were the actual "air mass" properties at that location.

Here's an email on the subject of crop aided dew point readings from Pete Boulay at MN State Climate Office sent last August:

"Hello all,

There's been discussion about certain AWOS sites in Minnesota and their proximity to row crops, especially St. James. The dew point temperatures at sites like St. James are consistently higher than other locations during the high dew point season of July and August. Could the close proximity of actively transpiring crops be the explanation?

I wasn't quite hot enough on Thursday, so I did a little dew point experiment on August 12 using a "pshychro-dyne" instrument. I measured the wet and dry bulb temperature at the St. Paul Campus Weather Station and the small, but dense corn plot in front of the station. It was a sunny day with very few clouds. Winds were light before noon, but became fairly breezy from the south by afternoon. Readings were measured at 5ft above the ground and were conducted in either shade or in the instrument shelter.

Here's a photo of the instrument used.

http://www.geneq.com/catalog/en/bop_pd.html

First value (T) is dry bulb, the second value (Tw) is wet bulb, the third value (Td) is dew point temperature. Dew point temperature was calculated at http://www.csgnetwork.com/dewptrelhumcalc.html All are in degrees F.

August 12, 2010

11:18am field by parking lot 1/3rd mile south of station T85 Tw75 Td71

11:30am middle of corn next to station to south T87 Tw79 Td76 (light wind)

11:33am in instrument shelter T88 Tw76 Td71 (light wind)

4:40pm in instrument shelter T89 Tw78 Td74 (moderate south wind)

4:43pm in corn south of station T89 Tw79 Td75 (moderate south wind)

Campus station HMP35C reading

11:00am T86 Td76

Noon T89 Td76

4pm T90 Td78

5pm T90 Td79

Observations...

The dew point temperature was higher in the corn by 1-5 degrees F, wind may play a role.

It feels very hot and muggy in the middle of a corn field in August.

Pete Boulay

State Climatology Office

DNR - Division of Ecological and Water Resources"

Count me as one who believes the records should stand from Tuesday!

"Manhole Geyser" in Montreal:

Check out this incredible video after flooding rains in Montreal!

Second Phoenix Dust Storm this month:

Check out the second major dust storm in Phoenix this month!

I have witnessed and broadcast many "dust storm warnings" during 9 years in Arizona. These giant walls of dust are caused by the gust fronts from thunderstorms. The soil between Phoenix and Tucson is so loose and fine that dust is easily picked up and whisked airborne.

Most of these "Haboobs" flow from southeast to northwest into the Phoneix area on the prevailling "monsoon thunderstorm" winds.

And this...

PH