Thursday, June 28, 2012

The Coming Heat Wave

Updated at 7:40 p.m.: The high temperature for Thursday was 100 degrees F in Columbia, 4 degrees above the forecast.  New information indicates that the high for Friday would most likely be 106 degrees.  Our internal computer model is projecting 107 for Friday and 108 for Saturday.  Therefore, it is possible that the all-time record high could be broken on either of those days.  It will be an interesting weekend.
Forecast on Wednesday, June 27.  Image Credit: WLTX.
The last two summers have each been the hottest on record.  This year is not shaping up to be hotter than the previous two, but it may still make the record book.  The computer models all week have been projecting that the heat wave in the central part of the country would expand east and would be focused over the Carolinas by Friday.  Much of eastern Colorado and western Kansas have seen record high temperatures.  In fact, Las Animas, CO tied the all-time record high for Colorado with 114 degrees.

Surprisingly the heat wave will shift rapidly to the east.  The high temperature in Columbia on Wednesday was 89 degrees with a forecast of 102 degrees by Friday.  However, the speed with which the hot air is moving east combined with subsidence of the air may produce even hotter temperatures.  There is a chance of reaching the all-time record high either Friday or Saturday.

Forecast of 500 millibar (mb) heights for 12z Friday, June 29, 2012.  The forecast was made on Wednesday evening using the 00z data.  Note the two high pressure centers; one in the Southwest and the other over the Tennessee River Valley.  Image Credit: WSI.

The center of high pressure in the middle part of the troposphere will be centered over the Tennessee River Valley on Friday.  This is climatologically an ideal setting for record high temperatures on South Carolina.  The wind flow is from the northwest, thus the air is flowing downhill.  This adds to the heat from air compression and will likely continue through Saturday as the center moves over the Carolinas.

Forecast of 850 mb temperatures for Saturday evening June 30.  The model was initialized using 00z data Wednesday evening.  Note the greater than 24C air over South Carolina for this time.  Image Credit: WSI.

Meteorologists often look at the temperature at 850 millibars (mb) to determine the surface temperature potential.  This is particularly useful when the air is subsiding as it will be this weekend.  Note in the forecast map above that temperatures at that level (about 4,500 ft) will be greater than 24 degrees C.  Generally a temperature of 21 C relates to a potential high temperature of 100 F while a temperature of 27 C relates to a high temperature of 110 F.  Some of the models are predicting 26 C for Friday afternoon which will give Columbia a potential to break the all-time record of 107 F.  The temperature has been achieved six times since records began in 1887.

Obviously there is concern about the heat index.  However, a dry air mass moved into the area on Wednesday and the air is much drier than normal.  This may aid in temperatures passing record levels since dry air heats faster than moist air.  I do not think that the heat index will be much different from the actual temperature on Friday or Saturday.  The humidity may not be high enough to be a factor until Sunday.  This is when will may see a heat index near 110 degrees F.

All of the models agree on the overall pattern, however there are minor differences.  This will lead to some tweaking of the forecast in the coming days.  It will be an interesting weather event.  Try to bear it and stay tuned.

Remember that children and the elderly are the most vulnerable.  Pets will need plenty of shade and the water should be changed at least twice a day during the heat.  Avoid strenuous exercise between 11 a.m. and 7 p.m.