Lightning - 25 January 2018
* Last Night's Thunderstorms *
Thunderstorms developed about the ranges to the north of the Melbourne and Pakenham areas yesterday afternoon in humid and unstable conditions. Weak northwesterly steering winds allowed thunderstorms to ascend over the cooler seabreeze air below and become maintained as they moved across the eastern suburbs of Melbourne and the Pakenham area. Keysborough recorded 54 mm of rainfall in 2 hours with thunderstorm activity which corresponds to a 50-100 year Average Recurrence Interval (50-100 year event).
Apologies for the lack of heads up and conveying of warnings relating to these thunderstorms. I was a way from technology for most of yesterday afternoon and evening. This is why it is important to always get your information from more than one source, and always check the Bureau of Meteorology for current warnings.
Video: Lightning over Pakenham kindly submitted to the PakenhamWeather page by Lainie Hocart. * Language warning *
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Summer Solstice 2017
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* Summer Solstice 2017 - Part 1 *
Tomorrow morning at 3:27am will be the Summer Solstice, when the Sun is at its furthest south. However, it was today that the Sun appeared at its highest point in the sky and we experience the longest day of the year with a day length of 14 hours and 49 minutes. Tonight will be the shortest night of the year with the Sun setting at 8:41pm and rising at 5:54am tomorrow moirning.
The Summer Solstice occurs when the Earth’s south pole is tilted towards the Sun which can be seen by the angle of the boundary between day and night in the full disk satellite image animation from this morning. Note how Australia sees the sunlight before the northern hemisphere. Further note that the reflection of the Sun on the Earth's surface, which can be seen as the round bright patch (known as "sun glint") over the southern Pacific Ocean, is situated over the Tropic of Capricorn which marks the southernmost point where the Sun is directly overhead.
Sun and Moon information for Pakenham can be found on the PakenhamWeather website here: http://www.pakenhamweather.info/today.htm
Satellite imagery courtesy of Regional and Mesoscale Meteorology Branch at Colorado State University.
#vicweather #melbweather #solstice #summer #summersolstice
#PakenhamWeather #DidYouKnow
After a rather mild morning in the #Pakenham area with the temperature reaching 19.8°C at 7:04 am this morning thanks to the strong northerly winds, a cold front has traversed the Pakenham area, shifting winds cooler westerly and dropping the temperature into the low teens. But spare a thought for people in Gippsland where Bairnsdale has recorded a very balmy 25.9°C thanks to a combination of a standing mountain wave and a phenomenon known as the 'Föhn Effect'.
The prevailing strong north to northwesterly winds force air up the northern slopes of the Great Dividing Range which increases cloud and rainfall. In doing so, the rising air releases heat and loses much of its water vapour content. As the air descends on the leeward side of the Great Dividing Range over Gippsland, it warms and dries. Because the air has lost much of its original water vapour content, the descending air becomes warmer than that on the windward slopes. The subsiding warm and dry air decreases cloud cover and consequently rain in what's called a 'rain shadow effect'. This effect has combined with a persistent standing mountain wave that has formed in lee of the Great Dividing Range due to the occurrence of very specific atmospheric conditions; namely strong uni-directional winds increasing in speed with height, a low-level inversion at a height similar to that of the mountain peaks, and instability in the mid-levels of the atmosphere. The mountain wave forces air to more strongly accelerate towards the ground in the lee of the Great Dividing Range, further exacerbating the warming and drying while causing gusty conditions (East Sale has recorded a maximum wind gusts of 80 km/h which is unusual in a northerly wind regime).
This effect can be clearly seen on the satellite image animation as the sharp boundary between cloud and no cloud on the southern side of the ranges. The Bureau of Meteorology satellite viewer can be found here: http://satview.bom.gov.au/
#vicwea
On 21 August, the United States had the pleasure of experiencing an awe-inspiring total solar eclipse where the moon for a brief period of time, completely covered the sun allowing those to observe the corona of the sun. Many of you have probably seen the spectacular photos of the solar eclipse from the ground, but what about from space? This animation from NASA's Earth Polychromatic Imaging Camera on board the National Oceanic and Atmospheric Administration (NOAA) Deep Space Climate Observatory in orbit at 1.5 million kilometres from Earth, shows the moon casting a shadow over North America and provides a unique perspective most people may have never seen.
Animation source: https://www.nasa.gov/eclipsephotos
How a tipping bucket rain gauge works
#PakenhamWeather #DidYouKnow
Have you noticed that despite raining over the past 3 hours that only 0.2 mm of rainfall has been recorded? Read on to find out why:
How rainfall is recorded?
Rainfall is recorded with a specialised measuring device called a 'tipping bucket rain gauge' which consists of a funnel that collects and channels the precipitation through a small aperture located at the bottom of the funnel. As the precipitation passes through the aperture, it enters one of two small buckets that are mounted on a pivot axle. After a pre-set amount of precipitation enters the bucket (in this case 0.2 mm), the bucket “tips” under the weight of the rainfall, dumping the collected water through the bottom of the rain gauge while actuating a switch which then electronically transmits this "tip" to a base receiver station (weather station) that then interprets this "tip" as 0.2 mm of rainfall. This information is then added to the logs of the weather station and is used to populate the rainfall fields on the Pakenham Weather website and page. Watch the video which illustrates how a tipping bucket rain gauge works.
Factors that influence the amount of rainfall recorded.
A number of factors can influence how much rainfall is recorded by a tipping bucket rain gauge. Specifically relating to today:
1. Since it has not rained for a while (since Tuesday last week), there will be a build of dust in and on the walls of the funnel. This increases the "wetting factor" which essentially means that some portion of the rain within the funnel is absorbed by the dust requiring more rain in order for droplets to form and run down the walls of the funnel, through the aperture and into the tipping buckets.
2. The rain is mostly evapourating due to quite a dry and warm sub-cloud layer. The only droplets that really survive this process are larger droplets which are typically further apart from one another. This makes it less likely for one or more droplets to fall directly in
Summer Solstice 2016
#PakenhamWeather #DidYouKnow
* Summer Solstice 2016 - Part 1 *
Today at 9:44pm will be the Summer Solstice, when the Sun is at its furthest south. Consequently, today the Sun will appear at its highest point in the sky making an angle of 75.37° above the horizon at noon (1:16pm) locally in Pakenham. The Summer Solstice marks the longest day of the year and corresponding shortest night of the year with the Sun rising at 5:51am and setting at 8:41pm, a day length of 14 hours and 49 minutes.
The Summer Solstice occurs when the Earth’s south pole is tilted towards the Sun which can be seen by the angle of the boundary between day and night in the full disk satellite image animation from this morning. Note how Australia sees the sunlight before the northern hemisphere. Further note that the reflection of the Sun on the Earth's surface, which can be seen as the round bright patch (known as "sun glint") over the southern Pacific Ocean, is situated over the Tropic of Capricorn which marks the southernmost point where the Sun is directly overhead.
Sun and Moon information for Pakenham can be found on the PakenhamWeather website here: http://www.pakenhamweather.info/today.htm
Satellite imagery courtesy of Regional and Mesoscale Meteorology Branch at Colorado State University.
#vicweather #melbweather #solstice #summer #summersolstice
Winter Solstice 2016
#PakenhamWeather #DidYouKnow
* Winter Solstice - Part 1 *
Today at 8:34am was the Winter Solstice, when the Sun is at its furthest north and consequently, appears at its lowest point in the sky at noon. The Winter Solstice marks the shortest day of the year and corresponding longest night of the year with the Sun rising at 7:34am and setting at 5:05pm.
The Winter Solstice occurs when the Earth’s south pole is tilted away from the Sun which can be seen by the angle of the boundary between day and night in the full disk satellite image animation. Note how Australia remains in night longer than the northern hemisphere. Further note that the reflection of the Sun on the Earth's surface, which can be seen as the round bright patch (known as "sun glint"), is situated over the Tropic of Cancer over the northern Pacific Ocean and coincides with the northern hemisphere's longest day.
Satellite imagery courtesy of Regional and Mesoscale Meteorology Branch at Colorado State University.
#vicweather #melbweather #PakenhamWeather #solstice #winter #wintersolstice
Satellite Loop - 28-30 January 2016
The following video is a timelapse of 10 minute satellite imagery between 11am Thursday 28 January and 11am Saturday 30 January (today) from the weather observation satellite Himawari-8. The thunderstorms that impacted the #Pakenham area can be seen toward the start of the video, followed by the developing cloud band that produced the significant rainfall over the Pakenham area yesterday. The parent low can be seen to the west of Victoria as the spiraling mass of cloud moving slowly northeastwards.
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For those that recall my post Saturday (https://www.facebook.com/PakenhamWeather/posts/1726122134285758) about giving the fire fighters at the Scotburn - Finns Rd fire located south of Ballarat a heads up about a wind change from a thunderstorm outflow, this timelapse video of the fire by Rob Cavanagh Photography shows the impact of the wind change on the fire and why they are so dangerous for fire crews on the ground.
Typically, a fire moves in the direction of the prevailing wind along a relatively narrow front which in this case was towards the south-southeast with an elongated trail of fire following. When the west to southwesterly wind change moved through, the elongated trailing fire suddenly becomes a much wider fire front moving towards the east to northeast. The danger is that, due to the rapid change in the size and direction of the fire front, any firefighters on the eastern side of the fire were in danger and why it is so important to let the firefighters on the ground know of any impending wind changes.
Video originally posted here: https://www.facebook.com/robcavanaghphotography/videos/1690504814552036/?theater
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Awesome!!! Check out this slow motion timelapse of a lightning strike in #Pakenham last night that beautifully demonstrates how a negatively charged "cloud to ground" lightning strike works.
1. The first four frames show the negatively charged downward stepped leaders which are effectively electrically conductive channels of partially ionized gas.
2. As the negatively charged leaders approach the positively charged ground increasing the localized electric field strength, an upward streamer of positive charge shoots from the ground toward the negatively charged leader.
3. When the two connect in a process known as "attachment", a low-resistance path is formed and discharge occurs as seen in frames 5 and 6.
4. The highly luminous electrical discharge is known as the "return stroke" and is the most visible part of the lightning strike as seen in the remaining frames.
Photos by Ricky Read.
Video composition by Pakenham Weather.
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Himawari 8 10-min loop of rainband 2015-08-27
#DidYouKnow
The rain that we have been experiencing today has been due to a developing low pressure system centred over the eastern ranges, directing and lifting warm moist air from the northeast to over much of Gippsland and the eastern suburbs of Melbourne resulting in cloud and rain. You can see this process in the 10-minute satellite imagery. These conditions are expected to persist for much of the day before easing this evening as the low gradually moves east overnight and over the Tasman Sea tomorrow.
Remember, IF IT'S FLOODED - FORGET IT!! Please take care on the roads and avoid swollen rivers and creeks.
#vicweather #melbweather #PakenhamWeather #weather #rain #Himawari #satellite #vicfloods
