An analysis of a flash flood caused by a lake-enhanced rainband is presente
d. The flood took place near Erie, Pennsylvania, on 17 September 1996. It w
as found that the hood resulted from a complex interplay of several scales
of forcing that converged over the Erie region. In particular, the flood oc
curred during a period when 1) a lake-enhanced convective rainband pivoted
over the city of Erie with the pivot point remaining quasi-stationary for a
bout 5 h; 2) a deep, surface-based no-shear layer, favorable for the develo
pment of strong lake-induced precipitation bands, passed over the eastern p
ortion of Lake Erie; 3) the direction of flow in the no-shear layer shifted
from shore parallel to onshore at an angle that maximized frictional conve
rgence; 4) an upper-level short-wave trough contributed to low-level conver
gence, lifting, and regional destabilization; and 5) a strong land-lake diu
rnal temperature difference produced a lake-scale disturbance that locally
enhanced the low-level convergence.
Analysis of the Weather Surveillance Radar-1988 Doppler radar data from Buf
falo, New York, and Cleveland, Ohio, revealed that most of the radar-derive
d precipitation estimates for the region were overdone except for the regio
n affected by the quasi-stationary rainband, which was underestimated. Reco
nstruction of the conditions in the vicinity of the band indicate that clou
d bases were considerably lower and equivalent potential temperatures highe
r than for the areas of precipitation farther east over northwestern Pennsy
lvania and southwestern New York State. It is postulated that, due to the l
ong distance from the radar sites to the Erie area, the radar was unable to
observe large amounts of cloud condensate produced by warm-rain processes
below 4 km. Estimates of precipitation rates from a simple cloud model supp
ort this interpretation.