![]() The exact line where advisories or warnings are issued by the National Weather Service varies region to region, generally a higher bar in southern and arid western parts of the nation, lower in northern and cooler higher elevation areas. Heat advisories and excessive heat warnings are based on the heat index. (With less moisture in the air, like the last few days, this perspiration-evaporation process works more efficiently, and the air can “feel” a little cooler than the actual temperature, hence a lower heat index reading than the air temperature.) When the air contains more moisture, evaporation becomes more difficult, and the body’s cooling mechanism is slowed the hotter and more humid it gets. But this cooling mechanism only works to maximum benefit if sweat droplets can evaporate. When temperatures rise, the human body sweats as a cooling mechanism. Thank you for your support of Cardinal News. Support our journalism by making your tax-deductible gift now. The idea behind the heat index is to provide a number for an approximate temperature as it affects the human body – or what it “feels like” – under various combinations of temperature and atmospheric moisture content. The cloud appears to be similar to lenticular clouds that often form in wind flow over mountains, though considering its proximity to towering cumulus clouds nearby, possibly could be a pileus cloud, formed by rapidly rising air, that broke off from the cumulus updraft. Matt Weddle captured this two-deck “flying saucer” near Rocky Mount in Franklin County on Wednesday, July 5. will circulate Canadian wildfire smoke in a way that we do not see much of it for several days.) This general pattern may hold most of the rest of July. (For now, it appears the trough in the north-central U.S. Cold fronts and disturbances moving southeast from the north-central states will increase those storm chances on occasion, and perhaps bring brief breaks from the hottest weather. that will bring some hot, sticky days with scattered afternoon showers and thunderstorms bubbling in the afternoon heat. Squarely under neither the hottest nor coolest air, Southwest and Southside Virginia will be at the edge of lesser high pressure over the Southeast U.S. We got a taste of it the past few days with some cooler mornings and not-humid afternoons, but the cool air will not overspread our region for longer, as appeared possible looking ahead from last week. ![]() Meanwhile, the core of cooler air will set up in an upper-level trough over the north-central U.S. The core of “heat dome” high pressure will park over the Desert Southwest, with many 110-120 temperatures, slightly hotter than normal highs there, even pushing toward 130 in Death Valley, California. That will again bring about some heat index values that could approach 100 degrees in sub-1,500-foot elevation areas like the urban floor of the Roanoke Valley, Southside and most locations east of the Blue Ridge. Stickier air will be returning to our region on southerly wind vectors off the warm Gulf of Mexico and Atlantic Ocean the rest of this week as temperatures rise back into the lower to mid 90s across much of our region’s lower elevations, and well into the 80s in most of the higher ones. ![]() With dew point values in the 50s and relative humidity values in the 30-40% range, the heat index was at times 1-3 degrees below air temperatures that rose well into the 80s to near 90. Then, slightly cooler, much less humid air moved in behind a cold front early this week. Heat index has become a relevant topic for Southwest and Southside Virginia in July.įirst, after a relatively cool June, temperatures rose to slightly above normal for several days in early July, while dew points, reflecting moisture levels and factored with temperature into figuring relative humidity, climbed into the steamy 60s and 70s, raising heat index values a few degrees above the 80s to lower 90s (and a few mid 90s) temperatures. Or, even better, just plug numbers for temperature and humidity or dew point into this online heat index calculator. The four shades ranging from yellow to red represent increasing levels of danger, from minimal to extreme. Match humidity values and temperature to figure out the heat index in this graph. It would probably be simpler just to look at the chart below. ![]()
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