134 Reasons Why Sticking A Weather Station In A Soy Field Might Not Be A Good Idea

With the recent heat event across the middle of the country, there have been countless stories about heat index values of over 120 degrees. I've mused in twitter about "corn effect" heat index values of 128, 130, or even higher. One of the most aggressive examples of this occurred in Moorhead, MN on Tuesday where the heat index topped out at 134 degrees during the peak heat of the day, thanks to a dew point of 88 combined with temperatures in the mid 90's.

Few probably realize that Moorhead's observation site is in the middle of a farm field ten miles outside of Moorhead proper.   The map below shows the twin cities of Fargo (left of graphic) and Moorhead (where the Google map "A" label is).   Residing about ten miles outside of the city is Moorhead's community airport (a municipal aviation airport such as the ones in Coatesville, Pottstown, Millville, etc.), sitting smack dab in the middle of a field of sugar beets, soy, and perhaps some corn for good measure.   I've been through this area a couple of times in my life -- the area is flat as a pancake, lacking trees, and heavily farmed.

The National Weather Service in Fargo provided a really good write up explaining the factors that lead to some suspicion in the high dew point values -- farming areas where heat index values are substantially higher than surrounding larger towns thanks to the transpiration of crops and wet ground.   Transpiration is the part of the water cycle on the plant side of the fence and essentially is the plant's way to cool itself as it releases water vapor through its cells.  Essentially, think a less stinky form of sweat.   I lifted the temperature comparison between Fargo's airport (a bit farther removed from agricultural influences) and Moorhead's airport data for Tuesday from the NWS in Fargo to show the comparison in data for the two sites.   The peak heat index for Fargo was 116 -- still oppressive -- but the top dew point for Fargo was five degrees lower than the top dew point in Moorhead (83 versus 88), with Fargo's dew point consistently several degrees lower than Moorhead's.

There are countless other examples of "corn effect" heat in these heat waves -- parts of Iowa and other parts of Minnesota had heat index values over 120 thanks to observation sites in the midst or near a farm field.   While some of the dew point values reached in the heat wave in the Midwest were legitimate -- the 82 in Minneapolis is a definite "legit" record since their airport is just about smack dab in the middle of the metropolitan area, the mid and upper 80's dew point values in some of the rural areas are likely enhanced thanks to what may be on someone's dinner plate, feeding trough, or gas tank (ethanol) in a few weeks.   There's no denying the heat or even the humidity in many locations but understanding should be taken when analyzing some of the more extreme data due to location and what surrounds it.

All I can ask is that tomorrow we don't get a dew point in the low 80's with any temperatures over 100...I don't think the region needs a repeat of July 1995 around here.

Heat Ridge About To Pump Temps Up

We're starting the core and prime heat days of our heat wave today, with three days of nastiness ahead where temperatures and dew points combine to make it feel like it's over 100 each afternoon...perhaps even as high as 110 in the prime heat of the day tomorrow afternoon.   Some low clouds, haze, and light fog graze the region this morning as residual less hot air from yesterday lingers while the heat ridge bubbles in from the southwest.   Temperatures are starting out on the toasty side regardless -- generally in the 70's and on the way to topping out well into the 90's by day's end.

Nationally, the main focus of the heat is shifting a bit to the east and southeast from its position of the past few days.   Minnesota and most of the Upper Midwest have seen the passage of a cool front and the introduction of some relief in the temperatures and humidity, with the heat dome shifting to the Ohio Valley and Appalachians for the next few days.  You can see the vast swath of real estate that are under some form of heat advisory, warning, or watch over the next couple of days (inland areas in a red shading) -- effectively close to 2000 miles from Massachusetts to Oklahoma.   Locally, we're under an excessive heat warning through Saturday.

Today's peak heat features heat index values between 102 and 107.   Based on an assumption that we reach high temperatures from 94-97 locally, with dew point values in the low or middle 70's, the heat index below is calculated for a number of different locations based on different combinations.   Even with a lower high temperature, a higher dew point can offset the "cooling" benefit of three degrees and give you an apparent temperature as high, if not higher, than the heat index of a locale with a higher temperature and lower dew point.   That's why it's more critical to know what the heat index is as opposed to simply knowing how high the air temperature is.    All of the air temperatures over the next three days will be hot -- perhaps record breaking in spots -- but the bigger story will be the combination of this heat with dew points that are borderline tropical.   That combination compounds air temperatures in the upper 90's or 100ish and makes it feel like it's a good 5-12 degrees warmer.

Most of us would probably feel better if we were talking about subzero wind chills this morning and not heat index values in the 100's or low 110's!   Regardless, stay cool (or as cool as possible) and drink lots of water.

More:  Current Weather Page

Excessive Heat Watches & Warnings Up

The prospect of the worst of the season's longest heat wave is coming upon us for late this week, with Excessive Heat Watches and Warnings out for much of the region due to the nasty combination of heat and humidity that is poised to worsen over the latter half of the week.   Excessive Heat Warnings are out for the Delaware Valley for now through at least Thursday, likely extending to Saturday given current trends, with watches out in Central Pennsylvania and in the New York Metro area for later this week.

We all know it's going to be hot, with computer guidance suggesting 100 is certainly within possibility for Friday and upper 90's sandwiching around that for both Thursday and Saturday.   The heat itself is bad enough and on Friday and Saturday, potentially record breaking.  However, the humidity will be the worse impact as dew point values in the lower 70's could yield heat index values upwards of 110 in some parts of town.   The heat/humidity combination is arguably much, much more potent and to be frank, it doesn't matter if anyone is forecasting 100 or not...the heat index will be higher and frankly makes the weather that much worse.

Thursday's records are rather tough to hit but Friday could pose a potential record breaking day, especially in Atlantic City and perhaps Philadelphia.  Saturday's record could be tied in many locations.   Even if we don't break a record, Friday will likely be the season's hottest day in terms of both temperatures and heat index.

Getting A Pumped Up Ridge

Channel your inner Hans and Frans -- Mother Nature is about to pump *clap* up the atmosphere with a ridge of high pressure in the mid atmosphere, resulting in a stretch of rather hot weather late next week or next weekend locally, with a run at 100 degrees not out of the question locally.

Mercifully, we will not see the worst of the heat and humidity.  That honor belongs to the Midwest, where this ridge will set up shop and temperatures could reach or breech 100 degrees in Minneapolis, Chicago, St. Louis, and other cities for a few days next week, with Chicago potentially seeing several days of upper 90's and near 100 degree temperatures.   This heat wave has the look of 1995's long duration heat wave to it...thankfully, it should not last as long but it could be just as nasty for Chicago and for the Midwest and it would not surprise me if there were fatalities in a number of the big cities from the heat.

 The question regarding "how hot we get" comes down to position of the upper ridge over us for Thursday-Saturday.   The GFS in the afternoon runs on Friday centered the ridge over the Appalachians, a pretty good spot for us to get some hot weather as upper levels are rather warm nearby.   The core of the heat ridge is near us and temperatures could approach 100 in such a scenario.  The Euro is a bit farther west with the heat core, over the Ohio Valley on Friday evening, which results in mid 90's for highs...still hot but not "prime heat."    The models have flipped and flopped over which scenario they prefer but in either scenario we're talking mid 90's, at least, for Thursday through Saturday.

If the "cooler" solution were to verify we could see some thunderstorm complexes track closer to the region around the periphery of the heat ridge.   The "ring of fire" of thunderstorm activity around the upper ridge is certainly possible...if the ridge isn't quite as strong or is centered a bit farther west we could see some thunderstorms in/close to the region during the heat event.

Factoring in humidity, heat index values could reach 105 during this time frame.   It will be oppressive but not as bad as in the Midwest, which could see heat index values around 120 on Monday or Tuesday in some locations.   The heat is back on...and this is likely the prime heat event for the year across the country.

Framing The Hot Talk Around Reality

What constitutes as "hot" and "heat wave" can be entirely subjective and at times the usage of both terms can lead to some discussion and debate over what's really a heat wave, what isn't, and what is hot and not.   There are truly hot days, such as Monday and Tuesday, as the combination of heat and humidity brings a higher temperature to the region and has it feeling much, much warmer than what the publicized air temperature is.   At the same time, there are days such as Sunday, when the high temperature is 90 degrees and the heat index is the same, perhaps lower, than the temperature.   Would have considered a day like Sunday hot? 

The "beauty" is in the eye of the beholder.

Let's first tackle "heat waves" since there is a clearly defined (whether you like it or not) approach to it.  In Philadelphia, the gold standard to measure "heat waves" is three or more days of high temperatures of 90 or higher, regardless of heat index.   While a three day heat wave in April (when the average high is in the upper 60's) or October (low 70's) is much more impressive than a three day heat wave in July (average high of 87), the definition is consistently applied throughout the year.   One of the big reasons for a clearly defined mark for heat waves in Philadelphia is the lack of air conditioning in many Philadelphia homes.    As many homes in the city are made of brick, heat radiating into the buildings effectively turns them into ovens...while you can't bake a pizza in a brick oven home, a person can bake to death.   The row home effectively becomes a death trap as temperatures rise inside the house to above 90, even on the ground level, at which point fans become ineffective.   While the numbers of homes in the city without air conditioning has decreased in recent years, a good number of the city's poorest and elderly still lack air conditioning.

The July 1993 heat wave in Philadelphia resulted in 118 deaths as temperatures climbed to 100 or 101 for three straight days and 90 or above for eleven in a row.   That heat wave is one of the more deadly in our nation's history and it drove a good deal of research among meteorologists and medical professionals to find preventive causes and measures to lower heat fatalities.   As a result, the heat advisory and warning system that we're used to seeing locally was pioneered here in the Delaware Valley by the National Weather Service and was used in a heat wave that blasted the region two years later.   Temperatures were quite hot (25 straight days of 89 or higher, 24 of them at/above 90) but the fatality level that year dropped to 72 despite a longer duration of heat compared to the '93 event.   

Those of us with air conditioning may think the "90 degree = hot" meme is a bit low, especially in July and that  using 90 as the definition for a heat wave is a bit low, especially in July.   However, that lack of air conditioning for the city's poorest is an issue and does lead to more sensitive reactions in the media...and perhaps justifiably so.

Whether we should redefine "hot" to a higher standard (mid 90's in midsummer, 90 before Memorial Day and after Labor Day) and whether the heat wave definition should change as well is sometimes up to debate.  I'm not convinced changing the heat wave definition on temperature locally is a good idea -- the city has essentially lived with 90 and three days as the definition of a heat wave for a while and has had this definition going back to prior to the '93 heat wave.    While three straight days with high temperatures of 90 or 91 constitutes a rather "cheap" heat wave in July for many, it still is rather warm for those who are outside all day or those who lack air conditioning.    Perhaps we extend the definition of heat wave to four days of 90 or higher?   This might help on the "cheap" heat waves but it doesn't necessarily capture the scope of a heat spike where temperatures for a couple of days are in the mid or upper 90's.  

One consideration is to develop an "ugly" scale for heat/humidity/duration, one that assigns points based on temperatures above 90, consecutive days, and departure from average.     If a particular threshold is crossed, you have yourself a heat wave?   Would be far more confusing than the current definition but it certainly would be good to use in comparison of "ugly" historically...much like the WAR statistic in baseball or PER in basketball, which are metrics that stataholics have developed to measure players to each other.

Given our climate in summer (July's average high is 86, 87 degrees), we'll probably always have the heat debate flare up from time to time in the heat of summer.  While heat is definitely subjective as some of us have higher tolerance of heat than others, I think the heat wave definition is one that...at least for now...should be left as it is.   While it's not perfect, it at least provides a clear definition that many can understand as many folks do think 90 is hot, regardless of the time of the year.

Ending The Heat For A Spell

Thanks to additional clouds and the instability that sparked this afternoon's downpours of thunderstorm activity locally, highs did not reach 90 in or close to the Philadelphia area.   It ends the season's longest heat wave to date for Philadelphia at five days.    Last year's longest heat wave was six days (twice), with four other heat waves of five days.

Year-to-date, Philadelphia has picked up 13 90 degree days, nine behind the pace set last year (22 through 7/8/2010).   It's pretty clear that breaking last year's record may be a tough act to accomplish at this point considering that July and August of 2010 combined for 31 90 degree days.

Second Heat Event Of Summer Looms

We're a couple of days away from the beginning of our second heat event of the year. Whether it makes it to a heat wave by hitting on 90 remains to be seen but we will get two hot to very hot days, perhaps three, this week before we enter a more unsettled pattern for the weekend as a front stalls out nearby.   The combination of surface high pressure off of the Carolinas and very warm temperatures aloft will allow the heat that brought 100 degree temperatures to Texas and Louisiana the past couple of days to work its way northeast and torch us.

Computer modeling suggests Thursday is the hottest of the upcoming stretch as high temperatures could approach record levels in Philadelphia.   The record for Thursday is 98 and we're predicting 96 in our forecast for Thursday.  Whether it hits or not is not important...the combination of heat and dewpoints in the 60's will bring heat index values close to 100 to the region, which is rather nasty regardless of whether the surface temperature is 95, 96, or 98 as it's gonna be hot.   Heat will even impact the Shore pre sea breeze in the afternoon as the surface winds will generally be west and west-southwest.  Expect highs in the 80's Wednesday-Friday at the Shore Points each day, with temperatures quickly reaching 90 as you get a mile or two inland.

A cool front will try to slide through the region -- whether that occurs early in the day Friday or on Friday afternoon remains to be seen but the front's bigger story is its predicted stalling out over the Mid Atlantic.  Assuming the front does stall out, an unsettled weekend with scattered thunderstorms looms for both Saturday and Sunday.   The one thing the front should be able to do is bring an end to the heat.   Unfortunately, the potential price to pay is a less than stellar weekend but after reaching the 90's for two to three days, some may be willing to pay that price.   Thunder will not occur all weekend long but neither day looks completely dry and thunderstorms will be scattered about more numerous in the afternoon both days this coming weekend.