From: Greg Bond
Subject: Notes on recent duststorm.

Hi John,

Here are some notes on the recent events. I have sent down, hopefully this am the regional mslp charts, soundings from the event and a couplefrom last night for comparisons. Luckily it's a holiday down yr way tomorrow so u should get them Wed. I have tried to quickly reanalyse the charts overnight as they were AVN working charts and a little rough around the edges at times. All the above are NOT needed back here. Don't have any ready access to upper charts or actual hourly AWS reports,
especially at this time of the day.

I arrived for the day shift and on briefing noticed on sat imagery an interesting area over SW Qld and its tracing back to NE SA the previous night. It was neither temp variations or cld. Previous shift sort of noticed it but said there was some dust about and it cud be some. It was clearly wedged in behind a "frontal zone". The dust was verified on the 21Z vis/ir imagery and daylight synoptic obs. Hurried forecasts predicted that it cud easily reach the east coast later in the day but we had never ?? forecast duststorms to this area before. We put out a media release as it was the only way of "warning " the people as is did not satisfy any other warning type category. Of course, the release did what is shud do but not to the benefit of us poor people. The phones broke loose and the rest is history. We actually had 2 extra people here to cope. My comments about the only time in 30 + yrs was originally confined to the observation of such a strong signature on sat pics but got lost in the translations to the best I've seen in 30+ years which is also probably true but must be put in context. We certainly have more obs than before and better sat pics. However other reports then to support the time lines. We forecast that thick dust would develop following the trough passage with strong WSW winds. No wx was forecast with the change but some did occur near the seabreezes front here and a little further inland  somewhat northwards.  Summary of some of the
important points ....

1. There was little temperature differences near the wind change. Temps were cooler overnight ahead due to radiational cooling in clear dry airmass and warmer following due mechanical mixing. Any cold (cooler ) air seemed to lie a lot further west. Dust was clearly confined to the west of the tr but as above not necessarily in the "cold" air, particularily the more vertically thick section as per sat pics.

2. Only a few reports of duststorm ahead of trough, mostly adjacent to passage. That was also apparent here in Brisbane when dust was extensive to the near west but change hadn't gone thru. Not sure if any density current and not familiar with a haboob (or any  boob !!!) type appearance.

3. This was a very strong impressive trough. Memory is low these daysand mostly confined to my last few bundy and cokes but was certainly one of the strongest seen for a while. 3 hr pressure falls over Qld peaked at 3.3 hpa ( which I believe would be historically high in October )whilst in NSW/VIc at 5.1 hpa which must be somewhat common. As we always try to relate things to commoly held ideas on radio I was sometimes quoting the unusual mslp over se parts in the pm, eg 993 hpa at Bris and 989 hpa at Coffs Harbour in relation to tc's in the tropics. There was certainly many comments on the extremely low pressures. I didn't have any records at hand but I see someone on yr page quoted near record October mslp's.

4. Trough movement was very fast but I don't believe the fastest but don't forget the memory component.  Averaged 34 knots over 24 hrs 6pm Tues to 6pm Wed which is not bad for southern Qld latitudes over 24 hrs.

5. Pressure gradient was generally tighter behind the tr but tended to become the opposite when closer to the coast due to p-gradients being enhanced but thermal gradients with strong seabreezes operating along the coastal strip. Certainly from over South Aust to early/mid Wed the former was true.

6. Visibilities were down to 8000m overnight Tues but reduced to 0 mm during the day with many reports below 500m. (see chart for full details) As noticed here and up in the NE tropics the next day, sunshine had a marked effect on reported reductions in visibilities due to refractions. Worst visibilities reported at 9am and 3pm but more manual obs these times.

7. From temperature soundings that morning, Moree was very unstable but the previous night's not as absolutely unstable as say last night's (Sunday 03/11). Brisbane has sig inversion that morning which would have mixed out over adjacent inland parts in the pm. The night sounding still showed a weak inversion on the coast and no effects of the tr passage which was 2/3 hours earlier which implied that the "colder" air was still to the west even though vis had been reduced following the wind
change. Vis reductions not dramatic at Bris airport due to nightime trends noticed previously. It was unfortunate we did not get a 11Z Charleville tsounding on the 22nd, some 9 hrs before the passage. Even so, the CV 23Z 22/20 trace clearly showed sig instability in the boundary layer 3 hrs after passage with warming spike close to the ground.

8. Why does/did the dust get picked up behind the front? It seems to happen in most/ nearly all events of late and probably in previous years even with much weaker ones than this one. Out in the far southwest of Qld, little or no vegetation due to the drought and the adjacent deserts will tend to give rise to dust ahead of and behind most troughs. But clearly all the dust in this event was reported adjacent to and extensively following the tr. On the radio I genetically describing the event like a " cold front"  but clearly in hindsight this was probably not true.  On the radio we try to keep to simple ideas they are fimilar with. Clearly the S'lies behind the front were stronger than the NW/N winds ahead of it. Without going back through the AWS hourlies, don't recall any significant gustiness in the AWS's at/post frontal passage. Once again, winds were not noticeably stronger than say a good hot unstable westerly mixing day over SE Qld and have seen much stronger(50%) winds over the tropical interior a couple of months ago due to differential heating effects which certainly seemed more likel a cold front than this one.

John, I've just about exhausted myself for this hour of the morning. Hope the above is of some use to you. Cud be more conprehensive but data is limited for now. Give us a yell if u need any more info.

Cheers
Bondy