Warren Eckels
Is there a sweet spot regarding dewpoint depression at 850 mb that promotes convection, or is the rule simply "the more moisture, the better"?
I', asking because a thin line of garden-variety thunderstorms approached Lake County, Indiana around 1:00 pm; they were entering a regime of surface temperatures and surface dewpoints that was slightly lower than the Illinois regime which maintained them well below severe guidelines.
At about 1:40, a storm W of Crown Point blew up as it moved northeastward. Winds approached severe levels in Merrillville as the line broadened and backfilled. Around 2:15 pm on an errand, I saw a cell behind the line started to develop near the I-65/US 30 interchange. Maybe I'm imagining things, but I thought I saw a wall cloud develop. (The winds immediately behind the squall line were from the ESE, upper level winds were from the southwest, but weak).
It seemes strange that a squall line would wait until it reached a region of lower CAPE to intensify. One somewhat unusual factor was a pool of relatively dry air at 850 mb behind the remnants of Tropical Storm Arlene; the intensification coincided rather nicely with that increase in T-Td at 850 mb.
Have any of you observed a similar situation, that is, an increase in storm intensity coincident with a decrease in moisture at 850 mb? (Around here, 850 mb was about 1300 m overhead yesterday).
I', asking because a thin line of garden-variety thunderstorms approached Lake County, Indiana around 1:00 pm; they were entering a regime of surface temperatures and surface dewpoints that was slightly lower than the Illinois regime which maintained them well below severe guidelines.
At about 1:40, a storm W of Crown Point blew up as it moved northeastward. Winds approached severe levels in Merrillville as the line broadened and backfilled. Around 2:15 pm on an errand, I saw a cell behind the line started to develop near the I-65/US 30 interchange. Maybe I'm imagining things, but I thought I saw a wall cloud develop. (The winds immediately behind the squall line were from the ESE, upper level winds were from the southwest, but weak).
It seemes strange that a squall line would wait until it reached a region of lower CAPE to intensify. One somewhat unusual factor was a pool of relatively dry air at 850 mb behind the remnants of Tropical Storm Arlene; the intensification coincided rather nicely with that increase in T-Td at 850 mb.
Have any of you observed a similar situation, that is, an increase in storm intensity coincident with a decrease in moisture at 850 mb? (Around here, 850 mb was about 1300 m overhead yesterday).