David Demko
An interesting situation in the hills and mountains of far southeastern Oklahoma and west-central Arkansas, as it appears that snowfall totals from the recent storm were considerably greater in the higher elevations of the Ouachita Mountains than the surrounding lowlands and valleys. WFO Tulsa talks about this in their post-storm summary:
I began to wonder if this might be the case yesterday when surface temperatures (as measured at ASOS, AWOS, and Oklahoma Mesonet stations -- all generally located at lower elevations) in that region were hovering around or just above freezing during the event.
With relatively warm air temperatures, and an already warm ground (5 cm sod temperatures were in the mid-40's), snowfall accumulation efficiencies could not have been all that great. Indeed, judging by the local storm reports, accumulations seem to be confined to the 3 to 6 inch range across most of northern Le Flore County, Oklahoma, and Sebastian County, Arkansas, despite a fairly long duration moderate to heavy snow event. Across more rugged areas in the southern reaches of those same counties, however, accumulations of 10 to 14 inches (such as the 14 inch total reported 6 NE of Big Cedar, OK near the Talimena scenic highway in southern Le Flore County) are common. WFO Tulsa indicates an "observed" total of 20 inches on their map in far southern Le Flore County, but I never saw a LSR for that one (they did mention the "estimate" of 20 inches in their post-storm statement though).
As those who have had the great pleasure of trying to chase in this area can undoubtedly attest to, some of the ridge tops across southern Le Flore County and surrounding areas are rather tall, reaching over 2500 feet above mean sea level (most ridges generally between 1750 and 2250 feet AMSL). Valley elevations are typically around 500 to 700 feet AMSL. See this shaded relief map. The elevation of the Talihina (TALI) and Wister (WIST) Oklahoma Mesonet sites (both in Le Flore County) are 669 feet AMSL and 469 feet AMSL, respectively. Surface air temperatures at both sites never once fell below freezing for the duration of the snow event (both hovered around 33F). The FSM ASOS (~460 feet AMSL) seemed pegged at 33F too.
Regional soundings appear to indicate that a relatively well-mixed, though shallow (about 50 mb deep), boundary layer existed in this area. The 2008-03-06 1800 UTC Fort Worth, TX sounding, launched as the heavier rain and snow was beginning to move through the DFW metro, gave a surface temperature of 34F and a 2000 feet AGL temperature of 27F. So, assuming a nearly identical near-surface thermodynamic profile existed farther north and east hours later, the 1000 to 1750 feet elevation differential from lowlands to ridge tops across SE OK and W AR would equate to a temperature drop of roughly 3F to 6F from valley to peak...giving ridge top air temperatures closer to 28F (valley temp 33F) and providing for much more efficient snow accumulation in the highlands.
There were likely some other factors in play here which aided in the enhanced accumulations -- including what looks to be generally higher liquid-equivalent precipitation totals toward the south and east and possible localized orograpic lifting effects, the latter of which is near to impossible to quantify. However, all things being equal, if air temperatures were in fact in the mid to upper-20's on the ridgelines while valleys remained above freezing, I would expect that the impact on snow accumulation totals would be considerable.
Just really interesting to see a phenomena more commonly thought of being associated with the Rockies, Pacific coastal ranges, Sierra Nevada, Appalachians, etc. manifesting itself in Oklahoma and Arkansas' little Ouachita range! I would certainly be interested to know if any Stormtrackers have firsthand observations of this or additional meteorological insight.
Snowfall accumulation map from WFO Tulsa
I began to wonder if this might be the case yesterday when surface temperatures (as measured at ASOS, AWOS, and Oklahoma Mesonet stations -- all generally located at lower elevations) in that region were hovering around or just above freezing during the event.
With relatively warm air temperatures, and an already warm ground (5 cm sod temperatures were in the mid-40's), snowfall accumulation efficiencies could not have been all that great. Indeed, judging by the local storm reports, accumulations seem to be confined to the 3 to 6 inch range across most of northern Le Flore County, Oklahoma, and Sebastian County, Arkansas, despite a fairly long duration moderate to heavy snow event. Across more rugged areas in the southern reaches of those same counties, however, accumulations of 10 to 14 inches (such as the 14 inch total reported 6 NE of Big Cedar, OK near the Talimena scenic highway in southern Le Flore County) are common. WFO Tulsa indicates an "observed" total of 20 inches on their map in far southern Le Flore County, but I never saw a LSR for that one (they did mention the "estimate" of 20 inches in their post-storm statement though).
As those who have had the great pleasure of trying to chase in this area can undoubtedly attest to, some of the ridge tops across southern Le Flore County and surrounding areas are rather tall, reaching over 2500 feet above mean sea level (most ridges generally between 1750 and 2250 feet AMSL). Valley elevations are typically around 500 to 700 feet AMSL. See this shaded relief map. The elevation of the Talihina (TALI) and Wister (WIST) Oklahoma Mesonet sites (both in Le Flore County) are 669 feet AMSL and 469 feet AMSL, respectively. Surface air temperatures at both sites never once fell below freezing for the duration of the snow event (both hovered around 33F). The FSM ASOS (~460 feet AMSL) seemed pegged at 33F too.
Regional soundings appear to indicate that a relatively well-mixed, though shallow (about 50 mb deep), boundary layer existed in this area. The 2008-03-06 1800 UTC Fort Worth, TX sounding, launched as the heavier rain and snow was beginning to move through the DFW metro, gave a surface temperature of 34F and a 2000 feet AGL temperature of 27F. So, assuming a nearly identical near-surface thermodynamic profile existed farther north and east hours later, the 1000 to 1750 feet elevation differential from lowlands to ridge tops across SE OK and W AR would equate to a temperature drop of roughly 3F to 6F from valley to peak...giving ridge top air temperatures closer to 28F (valley temp 33F) and providing for much more efficient snow accumulation in the highlands.
There were likely some other factors in play here which aided in the enhanced accumulations -- including what looks to be generally higher liquid-equivalent precipitation totals toward the south and east and possible localized orograpic lifting effects, the latter of which is near to impossible to quantify. However, all things being equal, if air temperatures were in fact in the mid to upper-20's on the ridgelines while valleys remained above freezing, I would expect that the impact on snow accumulation totals would be considerable.
Just really interesting to see a phenomena more commonly thought of being associated with the Rockies, Pacific coastal ranges, Sierra Nevada, Appalachians, etc. manifesting itself in Oklahoma and Arkansas' little Ouachita range! I would certainly be interested to know if any Stormtrackers have firsthand observations of this or additional meteorological insight.
