Michael Thompson's Australian
Storm Chase Diary
15th
March 2004 - Severe storm, Coastal Illawarra
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A
four shot panorama of the storm over Lake Illawarra. The sun was
visible through the rear, hence the wide contrast.
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Marginal
days are easily overlooked, sometimes to the extent that some little key
indicators are missed. Today was such a day. An unexciting surface chart,
weak broad trough and marginal indices such as Lift Index and CAPE had
me dismissing the day before it even started. What did I miss - very humid
coastal air, a weak upper trough and a fairly decent wind speed
shear.
At
work around 2.30pm I looked towards the SW and was surprised to see a
small cell developing about 100kms away. I checked the radar and this
cell was not showing anything at this stage, but what did take my attention
was a storm just north of Batemans Bay, about 150 kms S/SW.
Over
the next two hours the storm worked itself up the coast. By 4.30pm it
was near Nowra and I could no longer resist, so I knocked off work and
headed southwards.
It
was evident that wind shear was strong - as demonstrated by the photos
below courtesy of Stephen Jarret ( Lightning Chaser ).
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There
are two things I like when I see a storm like this. Firstly, the
evident wind shear, and secondly, the lack of other storms. Storms
in strongly sheared environments often do not look that impressive,
but I will gladly swap a pulse bomb for this anyday.
Photos
courtesy of Stephen Jarrett
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A
gust front quickly outruns it's parent storm and stalls just north
of me. |
I
made my way southwards down the coast, at Mount Pleasant south of Kiama
I finally came close enough to pull and take some photos. A large detached
gust front was moving up quickly from the south, in fact so quickly that
over the next 20 mins it outran the parent storm by some 20 -30 kilometres.
At this stage the decaying storm back south held no more interest for
me...what did interest however was the gust front, which had now stalled.
Humid NE winds were converging into this stalled outflow boundary. I knew
that this boundary would be the site of a new storm, so headed northwards.
From
here on things happened rather quickly. At Lake Illawarra a huge rain
free base loomed overhead. To the west the sun was visible through a curtain
of heavy rain.
The
lightning became very intense with bolts every few seconds within a kilometre
radius. The updraft base began to be cut by intense rain from the west,
I suspected that some RFD action was causing this. As the RFD cut in,
some weak circulation developed and rain curtains at one stage displayed
differential motion. Then the intense heavy rain and wind enveloped me.
I tried in vain to move ahead of the storm, but it was moving far too
quickly. Localised flash flooding occurred in around the suburbs surrounding
Lake Illawarra, there was some minor tree branches down, but no serious
damage.
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At
this stage lightning strikes became very intense and frequent. Cloud
motion was significant. |
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Just
seconds before being enveloped in torrential rain and 45 knot winds.
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Some
minor local flash flooding |
  
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