Sunday, July 17, 2016

Summer 2016 will likely be remembered for unrelenting heat

The summer of 2016 (at least meteorological summer, which consists of June, July, and August) is halfway over, and though not record-breaking, it has certainly been consistently hot!

While Memphis hasn't officially reached 100° yet this summer, perhaps the most notable statistics are related to the unrelenting duration of the heat. We simply haven't caught a break yet this summer! Unfortunately, both the short-term and longer-term forecasts do not offer a lot of hope for those tired of the heat. First, a little more about the heat of the past month and a half...

Summer 2016 Heat Statistics

Last month was the seventh warmest June on record in Memphis as high temperatures averaged nearly four degrees above the long-term average of 88.9° and low temperatures were more than three degrees above the climate average of 70.3°. So far, through the 16th, July has had an average high of 93.2° (1.6° above normal) and an average low of 76.1° (2.3° above normal) for an average temperature for the month that is nearly two degrees above normal.

Speaking of unrelenting, since June 1, the coolest high temperature has been 87°. We are in the midst of a streak of 32 consecutive days with high temperatures at or above 89° that started June 15. In fact, if it weren't for a high of 89° on July 11, that streak would be for temperatures at or above 90°. One additional statistic that speaks to the persistence of the heat is this: since May 24, only four days have had daily average temperatures below normal, and each of those was only 1-2° below normal. Despite all that heat, only two records have been set or tied and both were for warmest daily low temperatures (80° on June 25 and 81° on June 17). I'll say it again, we simply haven't caught a break!

An analysis of the departure from normal temperatures for the past 45 days (since June 2) shows the widespread nature of the warmth across the U.S. with the only below normal temperatures in central TX, along the CA coastline into the Pacific Northwest, along the U.S./Canadian border into New England, and a small portion of the Mid-Atlantic. Graphic courtesy WeatherBell.

Short-Term Forecast

Looking ahead in the short-term, upper level high pressure strengthens across the southern U.S. over the next day or so, then expands northward towards Canada into the Midwest. That means no relief in sight this week from the heat, and in fact, high temperatures on a few days could get near the warmest days so far this year (98° on three days in late June).

The GFS model shows a massive ridge of high pressure at 500mb (or about 18,000') centered over the Plains on Wednesday morning, which is representative of conditions for much of the coming week. Departures from normal conditions are indicated by color shading, with oranges being above normal and blues below normal. The strength of the high pressure indicates suppression of precipitation as weather systems move around the periphery of the high. Graphic courtesy WeatherBell.
The animation below shows the NWS National Blend of Models high temperatures from today through next Saturday. It is easy to see the heat expand as strong high pressure aloft causes the heat at the surface to get more intense. (If the animation doesn't play, click here to view it in a separate window.)

A weak upper-air disturbance will move into the region on Tuesday, perhaps bringing a thunderstorm or two, mainly to west TN, but that should have little effect on the temperatures that day, other than brief cooling for those that receive rain. With high pressure at the surface centered to our east, low level wind will be from the south, and you know what that means - the Gulf of Mexico will be "open for business!"

As moisture streams into the region from the south, expect daily heat indices to be over 100° as highs reach the mid to upper 90s. Some days will see heat indices of 105-110°, necessitating Heat Advisories. Next weekend, a slight weakening of the ridge could mean very low rain chances re-appear. However, if you work outdoors, please take the heat seriously and find time for breaks and drink plenty of water this week. Click here for the detailed week-ahead forecast from MWN, or consult our website or mobile app (links below).

Longer-Term Outlook

As for the long-term, there's actually little hope for the rest of July as that ridge of high pressure will be the dominating force. The NOAA Climate Prediction Center outlook for the past week of July indicates a very strong chance that above normal temperatures continue. Long-range climate models also indicate a likelihood of heat remaining in place to some extent through at least mid-August. It could be interesting to see where the meteorological summer of 2016 ends up when compared to some of the hottest summers on record (as of now, only 1980, 2010, 2011, 2007, and 1954 have been warmer).

NOAA/CPC predicts with high likelihood (nearly 60%) that above normal temperatures will continue from July 24-30. In fact, there is a high likelihood that all of the nation will experience above normal temperatures during this period except the Pacific Northwest.

NOAA/CPC also predicts a better than 50/50 chance that above normal temperatures continue for the first 2 weeks of August across the southern U.S. and west of the Continental Divide.
Stay cool!

Erik Proseus
MWN Meteorologist

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