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#1427834 - 11/07/2017 18:13 Re: Streamflow Observation [Re: Seira]
Seira Offline
Meteorological Motor Mouth

Registered: 27/08/2003
Posts: 6904
Loc: Adelaide Hills.
Modest Streamflow Response, Adelaide Hills:
5th to 8th of July 2017, following a Mostly Dry June


[Grammatical errors may persist despite editing]

18th of June 2017:

Sometime back between the 5th and 10th of June, the longer-wave trough, to the south of the Bight, sent a shorter-wave (upper-to-middle) off-shoot north-east [from south of Tasmania]. This off-shoot was subsequently undercut by the [surface] sub-tropical ridge (< shaped, with the \ being the undercut), changing the wind-direction from westerly to north-easterly on the eastern flank of the offshoot. It was thus lodged in a region between about Melbourne and Brisbane.

As the sub-tropical ridge directed E-to-ESE winds over interior Victoria from the south, moisture became diffuse and dissipated the further inland the winds moved (the Inter-Tropical Convergence Zone and 576-thickness contour situated near/north of Darwin, NT). With a lower tropospheric thickness, this absence of [inland] moisture (its accumulation, had temperatures possibly been higher) did not occur, hence dewpoints fell. The lower thickness would have then extended to sub-zero overnight lows, while the day-time maxima barely change (between Adelaide SA, Wollongong NSW and Melbourne VIC). Hence frost conditions ensued in the absence of sufficient cloud-cover.

Both the sub-tropical ridge and the main long-wave trough to the south of the Bight have been pushing east and NE, respectively. With the lodging of the tropospheric disturbance (on the East Coast between Melbourne and Brisbane), subsequent longer-wave troughs or lows (upper, middle or lower) have been unable to dislodge this disturbance. Thus, moisture north of the 576-thickness contour was tapped into [from the NE] in the Coral Sea [at the surface level]. This meant the middle-to-upper disturbance becoming lodged (again) west, against the Great Dividing Range, sustaining itself. The main longer-wave troughing (in deep south) has been continuing to push northeast.

The current pattern affecting SA (as 18th of June 2017) could change (properly) when the East Coast disturbance intensifies and moves further south. This would disrupt the west-to-east ridge movement, and shift the axis of the long-wave trough in the deep south, east. This is likely to happen in the next couple of days (19th to 22nd of June), with this transition forcing a part of the sub-tropical ridge in the South-eastern Indian Ocean (SEIO) to realign (/_ shape). This would also likely mean a part of the same ridge over Adelaide would be compressed, in the north-south orientation (forming a _> shape). The upper longer-wave troughs and lows would then be forced (through southerly winds on the eastern edge of the SEIO ridge) onto the eastern flank of the Indian-Ocean high (23rd to 26th of June), generating another offshoot (middle-to-upper level low).

A recent 2 mm on the 16th of June went straight into the soil locally. Minima of -2 to -6 C were mapped by the Bureau on the 10th of June across the inland Southeast and interior of the country.

21st of June 2017:

The winds on the eastern flank of the South-Western Western Australia (SW WA) offshoot became stronger, with the surface-based sub-tropical ridge continuing to push northeast. Simultaneously, the main long-wave trough south of the Bight (axis now shifted) blocked the southerly movement of the offshoot, forcing it up the WA Coast, and towards Adelaide (23rd to 26th of June). This meant winds on the south-eastern flank (with higher dewpoints and moisture content from the deep-south front) were dragged across SW WA. These ESE winds became affected by orographic uplift and land-sea temperature differences (warmer land). This generated heavy rain at several inland weather and streamflow sites (posted 23rd of June).

This is now starting to align the surface ridges /_\ where _ is the long-wave upper trough. This will likely release the SW-NE movement of the troughing [it becomes sharper and deeper], the pattern changing (between about the 27th of June and the 1st week of July).

26th of June 2017:

No significant changes to dynamics.

Streamflow levels (creeks/rivers/run-off) could possibly be affected by about early-mid July [2017] [SA].

30th of June-2nd of July 2017:

Possible rainfall range Sunday (late) 2nd to Thursday 6th of July: 15-40 mm.
Recorded: ~44 mm.

Estimated maximum rainfall (same period): 50 mm (Adelaide area).
Estimated region boundary: Whyalla to Mildura, to Omeo, to Melbourne to Port Lincoln.
Estimated run-off, minor-to-moderate (all run-off).

Rainfall of 50 to 99 mm recorded, followed by additional 25 to 49 mm falls [in SW WA region] as this system approaches (to 9 am, 2nd of July).

4th of July 2017, 5.25 pm ACST:

Streamflow levels (creeks/rivers/run-off) started responding (increasing) at 4 am, 3rd of July, with another storm at about 4 pm today increasing levels again.

Severe weather warning for heavy rainfall issued 4th of July, 4.45 pm ACST, another not long after.

Revised rainfall (4th): 50-80 mm in next 24-48 hours.

7th of July 2017, 9.15 pm ACST:

Recorded: ~34 mm last 3 days to 8.45 pm, 4th to 7th.

Streamflow now definitely responding (7th).
Bureau: 8 to 20 mm forecast tonight; 5 to 15 tomorrow.
At least 90% chance of any rain [6.44 pm ACST].

81.1 mm in 3 pm ACST, 10th of July, since 12 am on the 2nd of July (8 days). 69.5 more than all of June.

Disclaimer: as previous.
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#1428332 - 18/07/2017 15:21 Re: Streamflow Observation [Re: Seira]
Seira Offline
Meteorological Motor Mouth

Registered: 27/08/2003
Posts: 6904
Loc: Adelaide Hills.
The Upper Onkaparinga River stream level is responding to heavy rainfall: ~ 66 mm in the last 63 hours, 76 in the last week.
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#1428475 - 19/07/2017 21:01 Re: Streamflow Observation [Re: Seira]
Seira Offline
Meteorological Motor Mouth

Registered: 27/08/2003
Posts: 6904
Loc: Adelaide Hills.
Originally Posted By: Seira
The Upper Onkaparinga River stream level is responding to heavy rainfall: ~ 66 mm in the last 63 hours, 76 in the last week.

The flow at Woodside Weir reached 1.06 metres at 5 pm yesterday, after about 76 mm, 15th-18th, 12 am.
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#1428794 - 24/07/2017 20:36 Re: Streamflow Observation [Re: Seira]
Seira Offline
Meteorological Motor Mouth

Registered: 27/08/2003
Posts: 6904
Loc: Adelaide Hills.
Chance run-off in/near the Adelaide Hills will be affected sometime between the 27th and the end of July.


Edited by Seira (24/07/2017 20:37)
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