Paraparap Tornado
9th January 2000

The passage of a middle level cloudband across Central Victoria during the morning produced patchy light rain. At the Geelong Airport AWS, dewpoints reached 15C_dp at 1100AEDST with a surface temperature of 24C; the increase in dewpoint to this time probably reflected the occurrence of light rain in the area. Dewpoints decline steadily after 1200AEDST showing drying out of the surface layer. The official maximum temperature of 31.9C (Geelong AWS) at 1600AEDST was accompanied by a dewpoint of 11.1 C_dp. Interestingly, the arrival of a southeast sea breeze at about 1600AEDST did not significantly increase surface dewpoints.

The atmosphere remained rather dry from near surface to 817hPa (1850m). Between 817hPa and 707hPa (3035m), a sharp drop in temperature occurs. This is accompanied by a relative humidity increase from 50% to 95%. A moist layer then extends from 707hPa to approximately 582hPa (4566m). A very significant drying out occurs from 582 to 474hPa (6132m) from 67% to 7%RH. Generally speaking, the moisture profile remains rather dry above 474hPa to 300hPa (9390m) with variations between 15 & 39%RH.

For most of the afternoon (1200 - 1600AEDST), surface winds over the Paraparap area were predominantly northeast (30deg) with velocities between 5 and 12 knots (ex BoM Geelong Airport AWS). At about 1600AEDST, the surface flow tended southeast (130deg) and was probably associated with a sea breeze extending from Bass Strait, however airflow velocity remained at between 5 - 10 knots. The surface northeast to southeast flow was rather shallow and probably extended to about 300-400metres.

There is evidence of a marked backing above 500m with 355deg at 20knots shown for 750m. Airflow speeds average about 20knots from 750m to 3115m but directional shear continues backing to reach 300deg at 3115m. Speed shear declines slowly between 3115m and about 6000m with the slowest flow of 5knots at 5200m. Direction however continues to back from 300deg at 3115m to about 260deg at 6km. Above 6000m speed increases to about 25-29knots up to 9390m while direction continues to back from 260deg at 6km to 240deg at 9km. Although airflow speeds increase to over 30knots at about 10km, cloud tops did not penetrate above 9.3km during this event.

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