Urban Heating?

[JP Santiago]

Not sure if this has been linked to, but it might be of interest to the discussion about urban enviroments creating their own microclimates:

Link: http://www.livescience.com/environment/060...urban_arid.html
Link2: http://www.livescience.com/environment/050..._ecosystem.html

 

[Dan Robinson]

You city dwellers think you have it bad! In over 12 years of observing (and chasing) storms in the central Appalachians, I have seen an unmistakeable (maybe even obvious) pattern of storm dissipation due to a set of environmental factors. Storms will die 90% of the time upon approaching the Ohio River and the state of West Virginia. This 'Appalachian zone of dissipation' runs from the Tennessee-Kentucky border up to around Akron-Canton-Pittsburgh. This is no imagined phenomena either - watch it happen anytime.

In observing the storms and talking with local mets, I've come up with the following 'real' (non-imaginary) factors that supress convection as it approaches and crosses the state line from Ohio. Many of these are borderline obvious, but are worth mentioning.

1.) Inflow cutoff/damming - Southerly and easterly flow at and near the surface is physically cut off or suppressed by the high terrain of the Appalachians, which runs along the VA/WV border up through central PA and south along the NC/TN border.

2.) Orographic subsidence - Southerly or easterly flow crossing the mountains encourages sinking motion and downsloping effects (warming and drying, lowering of surface moisture and resultant CAPE). I have seen 'reverse drylines' take shape west of the mountains during strong downsloping. Td drops of 30F+ can be observed between Charleston and Lexington during these events, for example. Unlike CO, our terrain is a curse rather than a blessing - no DCVZ for us over here unfortunately.

3.) Timing/Diurnal effect - Climatology seems to favor storm initiation in Indiana and western Ohio by mid-afternoon in spring and summer, resulting in convection arriving at the border at or after sunset, simply due to timing issues. Loss of daytime heating alone or combined with the other factors results in storms dissipating.

On the rare occasion that storms initiate right on the border, inside of WV, or just into Ohio, storms can maintain their intensity. But most established complexes from the midwest will not make it to the crest of the mountains. Most will have no lightning left by the state line and no precip by the time it reaches the I-79 corridor.