By Tom Skilling
In a very real sense, thunderstorms are nature's air conditioners. They originate from the tallest clouds on earth---something which enables their rains to mix cooler air down to the surface to an extent beyond most shower clouds. It's a process able to temper extreme heat which might otherwise gain a foothold here.
The sweltering heat which has been draped across the southern U.S. From the deserts of the Southwest east to the Carolinas, has for the most part been deflected away from the Chicago area over the past three weeks. That's been a boon for Chicagoans who enjoy their early summer weather warm rather than blisteringly hot!
The numbers on the heat wave draped across the South are stunning. Highs the past 7 days at Dallas, TX have included readings of 94, 97, 96, 98, 97, 97 and 98. Equally impressive have been Savannah, Georgia's blistering highs of 95, 99, 95, 97,100, 102 and 99. At both locations, heat indexes have surged regularly into dangerous territory, passing 100-degrees.
But the heat-shielding effect of thunderstorms may be running its course. Cool thunderstorm outflows aren't likely to completely disappear from the scene in coming days and weeks. But hot temperatures appear likely to pay the Chicago area more frequent visits in coming days.
Friday's predicted 93-degree high---a reading 7-degrees above Thursday's 86 and the first temperature of 90 or higher in three weeks---would be the area's warmest in nearly a year. Such a high would surge past 2010's peak reading to-date of 91 set back on May 30.
What's more, when combined with sultry dew points predicted Friday afternoon to surge into the 70 to 75-degree range, a heat index of 99 to 105-degrees would result.
Severe weather a risk later Friday
Such heat might well contribute to severe thunderstorm development late Friday and/or Friday night. The Chicago area is outlooked for possible severe weather by NOAA's Oklahoma-based Storm Prediction Center. Projections of temperatures likely to decline more rapidly than usual with height, high atmospheric energy levels and shifting wind direction with height---a set-up referred to as "directional wind shear" by meteorologists---would meet the criteria for severe weather development. Strong storms appear a good bet, particularly with 90-degree temperatures and muggy 70-degree dew points in place.
Updated computer projections of Saturday's atmospheric structure here suggest a front may drop south through the area in the morning. This would have a stabilizing effect and might shunt any thunderstorm formation which takes place later Saturday farther south where the storms could become formidable again in the day's warmer hours.
Powerful storms rake the Plains Wednesday; 140 reports of severe weather
Severe weather, which has visited the Plains frequently in recent weeks, erupted again Wednesday across sections of Oklahoma and Kansas north to the high Plains of Colorado, western Nebraska and the western Dakotas. By late evening Wednesday, more than 160 reports of severe weather had been filed with the Storm Prediction Center.
Fastest demise of an El Nino in 12 years has Atlantic hurricane season & Chicago summer temp implications
Ocean temperatures along the equatorial Pacific west of South America have continued cooling and indications that a shift to full blown La Nina conditions is underway remain strong. The cooling has been the most rapid since 1998. NOAA long-range forecasters have placed the region under a La Nina watch. It's a development with implications not only to the 2010 hurricane season, which might well be enhanced by a La Nina, but also to U.S. summer weather. 11 of 14 La Nina summers on record in Chicago since 1950 have been warmer than average. The number of 90-degree or warmer days here in such years has varied widely---but has averaged 28 days. That's well above the 82-year average of 23 at Midway Airport.
In a very real sense, thunderstorms are nature's air conditioners. They originate from the tallest clouds on earth---something which enables their rains to mix cooler air down to the surface to an extent beyond most shower clouds. It's a process able to temper extreme heat which might otherwise gain a foothold here.
The sweltering heat which has been draped across the southern U.S. From the deserts of the Southwest east to the Carolinas, has for the most part been deflected away from the Chicago area over the past three weeks. That's been a boon for Chicagoans who enjoy their early summer weather warm rather than blisteringly hot!
The numbers on the heat wave draped across the South are stunning. Highs the past 7 days at Dallas, TX have included readings of 94, 97, 96, 98, 97, 97 and 98. Equally impressive have been Savannah, Georgia's blistering highs of 95, 99, 95, 97,100, 102 and 99. At both locations, heat indexes have surged regularly into dangerous territory, passing 100-degrees.
But the heat-shielding effect of thunderstorms may be running its course. Cool thunderstorm outflows aren't likely to completely disappear from the scene in coming days and weeks. But hot temperatures appear likely to pay the Chicago area more frequent visits in coming days.
Friday's predicted 93-degree high---a reading 7-degrees above Thursday's 86 and the first temperature of 90 or higher in three weeks---would be the area's warmest in nearly a year. Such a high would surge past 2010's peak reading to-date of 91 set back on May 30.
What's more, when combined with sultry dew points predicted Friday afternoon to surge into the 70 to 75-degree range, a heat index of 99 to 105-degrees would result.
Severe weather a risk later Friday
Such heat might well contribute to severe thunderstorm development late Friday and/or Friday night. The Chicago area is outlooked for possible severe weather by NOAA's Oklahoma-based Storm Prediction Center. Projections of temperatures likely to decline more rapidly than usual with height, high atmospheric energy levels and shifting wind direction with height---a set-up referred to as "directional wind shear" by meteorologists---would meet the criteria for severe weather development. Strong storms appear a good bet, particularly with 90-degree temperatures and muggy 70-degree dew points in place.
Updated computer projections of Saturday's atmospheric structure here suggest a front may drop south through the area in the morning. This would have a stabilizing effect and might shunt any thunderstorm formation which takes place later Saturday farther south where the storms could become formidable again in the day's warmer hours.
Powerful storms rake the Plains Wednesday; 140 reports of severe weather
Severe weather, which has visited the Plains frequently in recent weeks, erupted again Wednesday across sections of Oklahoma and Kansas north to the high Plains of Colorado, western Nebraska and the western Dakotas. By late evening Wednesday, more than 160 reports of severe weather had been filed with the Storm Prediction Center.
Fastest demise of an El Nino in 12 years has Atlantic hurricane season & Chicago summer temp implications
Ocean temperatures along the equatorial Pacific west of South America have continued cooling and indications that a shift to full blown La Nina conditions is underway remain strong. The cooling has been the most rapid since 1998. NOAA long-range forecasters have placed the region under a La Nina watch. It's a development with implications not only to the 2010 hurricane season, which might well be enhanced by a La Nina, but also to U.S. summer weather. 11 of 14 La Nina summers on record in Chicago since 1950 have been warmer than average. The number of 90-degree or warmer days here in such years has varied widely---but has averaged 28 days. That's well above the 82-year average of 23 at Midway Airport.
