Mapping the hottest day of the year in the USA

From NOAA/NCDC, something interesting: a new map showing when to expect hottest days of the year and where. The long thin line on the west coast is interesting because that is where the bulk of the population of each state lives and one might think that has something to do with it, but it is actually related to the marine layer.

Mercury Rising: When to Expect the “Warmest Day of the Year”

U.S. Warmest Day of the Year MapFollowing the first official day of summer, many areas in the United States are approaching their highest temperatures for the year. To give you a better idea of the warmest time of year for your area, NCDC has created a new “Warmest Day of the Year” map for the contiguous United States. The map is derived from the 1981–2010 U.S. Climate Normals, NCDC’s 30-year averages of climatological variables including the average high temperature for every day. From these values scientists can identify which day of the year, on average, has the highest maximum temperature, referred to here as the “warmest day.” 

Although the amount of solar radiation reaching the earth peaked at the summer solstice on June 21 in the Northern Hemisphere, temperatures for most of the United States tend to keep increasing into July. The temperature increase after the solstice occurs because the rate of heat input from the sun during the day continues to be greater than the cooling at night for several weeks, until temperatures start to descend in late July and early August.

But, this isn’t the case everywhere! The “Warmest Day of the Year” map shows just how variable the climate of the United States can be. For instance, the June values in New Mexico and Arizona reflect the North American Monsoon, a period of increased rainfall affecting the Southwest United States. Because these areas tend to be cloudier and wetter from July through September, the temperature is highest on average in June. Similarly, the persistence of the marine layer along the Pacific Coast leads to cool temperatures in early summer with the warmest days on average later in the season.

Temperature Normals are important indicators that are used in forecasting and monitoring by many U.S. economic sectors. Knowing the probability of high temperatures can help energy companies to prepare for rising electricity demand and farmers to monitor heat-sensitive crops. They are also useful planning tools for the healthcare, construction, and tourism industries. You may want to check the Normals before planning your next event or vacation.

While the map shows warmest days of the year on average throughout the United States, this year’s actual conditions may vary widely based on weather and climate patterns.

Source: http://www.ncdc.noaa.gov/news/mercury-rising-when-expect-warmest-day-year

h/t to Tom Peterson

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39 thoughts on “Mapping the hottest day of the year in the USA

  1. I don’t even have to look. I despise hot, humid weather but somehow wound up living in NJ where every summer is 3 months of interminable mugginess. My birthday happens to fall on July 18th and it never fails…hottest day of the year.

  2. Does the NCDC map created using real temperatures or NCDC ‘adjusted’ temperatures?

  3. Looking at their time scale on the bottom just clarified something for me…
    …they have 4 months to break hottest day records

  4. What a waste of time. Now if they could consistantly figure out the winner of the first three races at Aqueduct on any given day, I might actually be impressed,

  5. JohnH: Count yourself lucky. It usually snows on my birthday, and my birthday is in September…..

  6. As usual, Alaska and Hawaii seem no longer to be a part of the “United States” according to NOAA………..#-(

  7. As usual, Alaska and Hawaii seem no longer to be a part of the “United States” according to NOAA………..#-(

    But they aren’t connected, so 97% of pedants will say technically they are dis-united .

  8. Yeah, but out here in California we can’t say, “Yes, but it’s a moist heat” like they do in the South.

  9. Fall is summer here on the immediate West Coast (although Spring is up there too). Summer is as someone incorrectly quoted Mark Twain. We continue being entertained by tourists freezing in their shorts and t-shirts meanwhile we’re wearing our hoodies.

  10. Why does this data set only go back to 1981? There were no thermometers in the US during the first 8 decades of the 20th century?

  11. I thought with the new and improved NOAA maps only hyper reds were allowed and that everyday is a new record high for the US. “Doh!” – H.Simpson

  12. A map of Hours of Bright Sunshine for July would give a most interesting comparison.

  13. “The temperature increase after the solstice occurs because the rate of heat input from the sun during the day continues to be greater than the cooling at night for several weeks, until temperatures start to descend in late July and early August”

    As Hans Errin indicates above I don’t know that I buy this as the reason for the delay. Sitting here in Central Texas it is seems tied to the drying of the ground through July which leads us to the higher August temperatures.

  14. “tgasloli says:
    June 27, 2014 at 3:02 pm
    Why does this data set only go back to 1981? There were no thermometers in the US during the first 8 decades of the 20th century?”

    Yep, my thoughts exactly….there are records in some places going even farther back.
    I think they don’t want to show the 1930s, for instance, as they won’t be able to say
    “it’s the hottest ever” (since we started, erm, measuring, er, cooking the books,etc., etc.).

    Sixty year cycles probably have never occurred to them…then again, not much else does
    either, unless it’s got funding attached to it…

  15. With reference to ‘where is the page on “The Coldest Day o fthe Year”‘ which would be of interest to city managers with large homeless populations (to protect them from freezing to death) – send a note to the NOAA at: (from their web site)

    For Climate Monitoring Products and Analyses – Email: cmb.contact@noaa.gov

  16. I’ve been breathing for 51 years, been through droughts/floods/blizzards/lack of snow that freezes the ground to scary depths.
    What were we talking about ?

  17. Bill Illis (June 18, 2012 at 3:35 pm) wrote:
    =
    The seasonal lags for the ocean are about 82 days, freshwater lakes are about 49 days and land surfaces are 34 days.
    [...]
    It is big part of the picture; energy flows over time, that are not being addressed in the theory.
    =

    http://wattsupwiththat.com/2012/06/18/time-lags-in-the-climate-system/#comment-1012418

    _
    Bill Illis (December 7, 2008 at 6:25 am) wrote:
    =
    Land temperatures lag [...] the soltices by about 30 days. The hottest/coldest part of the year is 30 days after the summer/winter solstice.

    The oceans lag the equinox/solstice by about 80 days. The oceans are at their warmest 80 days after the solstice (hurricane season peaks on September 12th, polar ice melt peaks on September 12th, the actual sea surface temperatures peak on September 12th.)
    =

    http://wattsupwiththat.com/2008/11/25/adjusting-temperatures-for-the-enso-and-the-amo/#comment-61824

  18. Jeff says:
    June 27, 2014 at 4:13 pm
    “tgasloli says:
    June 27, 2014 at 3:02 pm
    Why does this data set only go back to 1981?

    Because “normal” in the context of weather is defined as a 30 year average with the final year ending in a zero. For example 2010. Shortly after 2020 rolls around the new-normals will be for 1991-2020. The idea is that most of us do not remember the 1930s so a perception of that warmth is not something of interest. But insofar as the weather seems to move in multi-decadal waves/cycles/oscillations (pick your term) then a recent 30 year period is more likely to catch the current year than if all the data is used – that just smears out things. Having established a purpose for the map, the creators thus chose a suitable metric.
    –————

    The long thin line on the west coast is interesting because that is where the bulk of the population of each state lives …

    This fits S. CA well but not WA & OR. Not really important to the post – just an observation.

  19. “John F. Hultquist says:
    June 27, 2014 at 5:23 pm ”

    The trouble is, 30 years (average or not) out of a longer cycle (60 years or so), are useless.
    I don’t care if folks don’t remember back that far, picking parts of cycles makes it all to easy to
    “lie with statistics” (truncated graphs, inconsistent indices, etc.).
    To quote Carly, “perception is reality” when it comes to the CAGW agenda, so a good dose of the truth, including numbers going as far back as is reasonable, is the best place to start.

  20. June 27, 2014
    Jeff says:
    June 27, 2014 at 5:54 pm

    For this purpose you want data that is consistent with the current direction of the metric – be that up, down, or sidewise. Say temperature is now going sidewise (aka “the pause”). It seems that including the low temperatures of the 1970s (if such there were) would detract, rather than add, to the reasonableness of the analysis. The phrase “muddy the water” comes to mind.
    Say you want to project the temperature at 5 PM. Would you plot Noon through 4 and make your guess or would you average the previous 24? Place your bet.

  21. The 30-year definition of “normal” was decided on long before there was such a thing as PDO, AMO, or el Nino, in the meteorological literature. Eons ago myself, perhaps 40 years ago, I read that the average of the preceding N years, with N ranging from 10 to 30 or so, had the best correlation with the current year or next year. So it was the best “predictor” of the current or near future temperature of, say, a month. For what it’s worth, because I can’t recall a reference for that at this time of night.
    As for daily “normals”, they are computed from the 12 monthly normals (from 30 year averages), to which an interpolation function (a running 3-month cubic fit, or a harmonic fit) creates a smooth curve from which daily values can be read. I’m a co-op observer (Coal Creek Canyon, CO), and over the past 30 years January has averaged a little warmer than December or February. So my daily normals have an odd bump in mid-winter. You eastern Yankees might call that the January thaw, but back east that’s not a big enough event to keep January from being the coldest month. In Colorado I think it has something to do with the regional north-south gradients causing westerly chinook winds to peak in January, which keeps nighttime minima a bit higher than December or February.
    I myself find that map fascinating and it’s fun to look at how the season lag varies so much and to speculate on why. The seasonal lag becomes a lead down in Big Bend, Texas, where the daily max peaks before the solstice. The early seasonal max across the southwest is due to the onset of the summer monsoon in July, which increases dew points and afternoon clouds and showers that cut off the rising temperatures before mid-afternoon.
    Meanwhile, the southern plains have a late seasonal max, and the line between the early and late seasonal max temps looks like the dry line, known and beloved by tornado chasers.
    Maybe they’ll put out a cold version in the Fall when folks are more interested. Since the link to the chart is http://www.ncdc.noaa.gov/file/us-warmest-day-year-mapjpg , I tried replacing “warm” with “cool” or “cold”, but no luck.

  22. I too found the map most interesting. Having lived in three of the four corners of the CONUS (missed out on Washington/Oregon) and now in South Central Texas , the map certainly coincides with my experience. It was interesting to move from coastal Southern California where the hottest days were during the first two weeks of September, to New England, where by the third week in August it was already starting to feel like fall.

    Note however, the map says nothing about the temperature magnitude of the hottest day. It is still hotter in Texas in June than it is in Connecticut.

  23. ‘Temperature Normals are important indicators that are used in forecasting and monitoring by many U.S. economic sectors’

    A bugbear that I have with forecasters in the UK, and I expect they’ll be the same around the world, is that they make statements along the lines of ” tomorrows temps will be two degrees above what we would expect at this time of year”. They seem unaware of the principle that norms are an average, and that a temperature two degrees above the norm is to be expected at least part of the time. Like tabloid headlines, there is a desire to make any news sound out of the ordinary.

  24. I didn’t think it was quite this variable across the US so for me this is interesting. I guess there are local factors which influence the day of peak summer and peak winter.

    It does however indicate an important physics phenomenon. Joules of energy accumulate and drawdown on the Earth’s surface on a per second basis throughout the day and there is net imbalance in those numbers on a daily basis through the seasonal cycle. One can actually calculate the joules involved here compared to the amount of energy coming in from the Sun and it is exceedingly small number.

    Energy comes in from the Sun, and it is almost immediately emitted back to space. Very, very small amounts can accumulate as the day warms up and peaks around 3:30 pm and then each day there is a small excess accumulating as it warms up after the peak of winter to the peak temperature of summer. But these accumulation rates are nothing compared to the Sun’s daily energy inflow.

    Energy and the speed that energy flows in and out of the system hasn’t been addressed by climate science that I have seen. Yet it is actually what is going on.

  25. “Because “normal” in the context of weather is defined as a 30 year average”

    Well that explains why weather related “science” does such a bad job at prediction and why everyone in “climate science” is so comfortable with “harmonizing” data. In no other field of science would you decide to toss out the bulk of data for an arbitrary averaging period. And you know you could convert the larger data set into 30 year rolling averages.

    This also helps to explain why the Ag department’s “improved” hardiness zones resulted in so many of us in the north with a yard full of dead plants this spring. The “improved” zone maps based on the prior 30 years wrongly coded plants that then couldn’t handle a normal winter.

  26. When I was recording temps living in forested western VA (2700 ft elevation), the date of the highest temp varied wildly — but ended up “average” around — July 21st. High elevation forested areas are nicely cool in summer:

    1987 — 90F, 8/22
    1988 — 91F, 8/17
    1989 — 83F, 7/11
    1990 — 87F, 7/9
    1991 — 86F, 7/22 & 7/23
    1992 — 84F, 7/13
    1993 — 85F, 7/7 & 7/9 & 7/10
    1994 — 85F, 6/15
    1995 — 86F, 8/17
    1996 — 87F, 5/19
    1997 — 86F, 8/17
    1998 — 86F, 7/21 & 9/14

    Avgs — 86F, 7/21

  27. Interpretive aid — includes informative land/ocean lag & gain maps:

    Stine, A.R.; & Huybers, P. (2012). Changes in the seasonal cycle of temperature and atmospheric circulation. Journal of Climate 25, 7362-7380.
    http://www.people.fas.harvard.edu/~phuybers/Doc/seasons_JofC2012.pdf (final)
    http://www.people.fas.harvard.edu/~phuybers/Doc/Seasons_and_circulation.pdf (preprint)
    =
    [...] gradients give rise to anomalous circulation, with this anomalous circulation then causing convergence or divergence of heat by acting across either the land-ocean temperature gradient (a mechanism which is particularly important in Northern Europe) or across the pole-to-equator temperature gradient (an important mechanism in Eastern North America and in East Asia).

    [...] the shift toward earlier seasons is not predicted by any of 72 simulations of twentieth-century climate made using 24 different general circulation models [...]

    [...] general circulation models forced with the observed twentieth-century forcing not only fail to capture observed trends in temperature seasonality, as mentioned, but also generally fail to reproduce the observed trends in atmospheric circulation [...]

    Thus, the hypothesis that changes in atmospheric circulation are responsible for changes in the structure of the seasonal cycle is consistent with the failure of general circulation models to reproduce the trends in either [...]
    =

  28. More maps exploring spatial structure of oceanality/continentality:

    McKinnon, K.A.; Stine, A.R.; & Huybers, P. (2013). The spatial structure of the annual cycle in surface temperature: amplitude, phase, and lagrangian history. Journal of Climate 26, 7852-7862.
    http://popo.sfsu.edu/~zan/Files/McKinnon_Stine_Huybers_2013.pdf (final)
    http://www.people.fas.harvard.edu/~phuybers/Doc/McKinnon_JofC2013.pdf (preprint)
    http://people.fas.harvard.edu/~mckinnon/Home/Publications_and_presentations_files/McKinnonEA2013_JClim_EOR.pdf (preprint)

  29. One thing I noticed was that the date of the hottest day strongly correlates with how humid an area is.
    Would it be possible to determine if the atmosphere has been getting more humid (as the models say it must) by tracking any changes in the average date of the hottest day?

  30. A few more links of historical interest:

    Mann, M.; & Park, J. (1996). Greenhouse warming and changes in the seasonal cycle of temperature: model versus observations. Geophysical Research Letters 23, 1111-1114.

    http://www.meteo.psu.edu/holocene/public_html/shared/articles/MannPark1996GRL.pdf

    Thomson, D.J. (1995). The seasons, global temperature, and precession. Science 268, 59-68.

    http://www.inventus.org/posterous/file/2009/04/228341-2886492.pdf

    With more careful attention to
    (a) SAM (Southern Annular Mode),
    (b) Sidorenkov’s (2009) section 8.7 (on equator-pole heat engines), &
    (c) the works of Jean Dickey (of NASA JPL),
    the error in the latter paper can be corrected.

  31. Illustrating the global context as concisely as possible:

    = map animation:
    surface temperature
    seasonal cycle amplitude / phase (slowly alternating maps)

    Credit:
    Dwyer+ (2012) (linked immediately above)

  32. Humm.

    The long thin line on the west coast is interesting because that is where the bulk of the population of each state lives

    Southern California – OK.
    Northern California – Not.
    Oregon Coast – Not.
    Washington Coast – Not.

  33. Randall_G says:
    June 28, 2014 at 8:12 pm

    Humm.

    The long thin line on the west coast is interesting because that is where the bulk of the population of each state lives

    Southern California – OK.
    Northern California – Not.

    ==========================

    Last I looked, we here in the Bay Area are in the thin line area for the most part. Only our inland suburbs are not.

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