July Update 2024 SA
July update 2024 SA
*Forecast
prepared between July 16th-18th 2024
Review:
G’Day
everyone, the mid-month update is upon us already as we move seemingly quickly
through this winter, already half over! It is good to see some green around now
after such a poor start to the year and growing season and I trust and hope
that most of you have received at least some form of break and are away with
the season however I do expect some poor areas namely through the Lower and
especially Upper North and also Mid-Mallee.
So far July
has seen quite a mixed bag of weather as we pull between more extremes for the
season. The most notable aspect has been the early month large and persistent
high-pressure systems sitting down near Tasmania giving us fresh to strong and
occasionally even damaging SE-NE winds, chiefly in the evening, gully winds
that we usually associate with the warmer months. That aspect was very unusual
for July. I have noted in the past sometimes before the polar vortex expansion
that we see an initial contraction phase which pulls the highs closer and
strengthens them.
Then, the
Longwave Trough that had been stuck to the SW of WA for a
number of months made a move east finally last week giving a decaying
rainband and a burst of westerlies. Now beyond this for the last week we have
seen a persistent onshore flow, with some significant streams rolling up from
the SW-S all thanks to a large and complex multi-centred low SE of Tasmania.
This really has retrograded and flung up multiple weak troughs around the
western flank giving us colder air, and showery conditions and light rainfall
totals ticking over each day, with some better penetration into the Lower and
Upper North at times due to the angle. At the time of writing, we have a good
stream running up the Spencer Gulf also giving further totals to the dry Cowell
area as well as the Melrose-Pt Germein and Booleroo regions on the other side
of the Spencer Gulf. Weekly totals generally have been in the 10-20mm range
across the Upper North with Port Germein receiving 23mm, Melrose 21mm and
Wilmington 19mm. Further south across the Lower North we have seen slightly
better falls with Mintaro and Hoyleton receiving 33mm each, Clare 31mm, Auburn
29mm and Farrell Flat 22mm. Jamestown, which has really copped the raw end of
the stick so far has received 10mm in the last week and is in that zone that
has been missing much of the westerly activity so more is needed and hopefully
today (17th) that can see some streams work well up into that
region.
Meteorological
Discussion:
Now getting
straight into current proceedings and we have a NW Cloud feeding in along a
jetstream and trough ahead of a strong cold front which will advance rapidly in
behind due into the state during the late afternoon and evening of the 19th.
The trough at first with the cloudband will bring areas of rain, patchy at
times but there should be some consistent rain areas at times from the
mid-morning across chiefly southern agricultural areas with that rain
thickening as it moves SE thanks to a highly divergent atmosphere aloft. Winds
will freshen from the N ahead of this trough and rain with strong winds likely
at times, especially about the southern coasts and exposed peaks. Once the rain
eases in the afternoon, the main cold front will bear down on the coastline
with winds becoming strong to gale force at times ahead of and on the cold
front. Damaging winds are likely, especially about exposed southern coasts,
ranges and general higher peaks with wind gusts likely in the 80-100km/hr range
but some isolated gust potential exists up to 120km/hr. A sheep graziers alert
has already been issued by the Bureau as well and is most warranted.
The cold
front itself will be vigourous, strengthening all the way
in with a band of showers along it followed by a negatively tilted cold pool.
This is one that leans eastwards with northern aspect and these types are
particularly strong so watch out for the post frontal cold air cells
immediately behind and for a few hours afterwards. Squally showers, heavy at
times with localised flash flooding are possible as well as isolated small hail
and cold air thunder. The vast majority of the
impacts will be increased south of about Adelaide, especially rain wise. The
strongest cells will likely be through once midnight comes and into the 20th
with general scattered showers to follow. Winds behind the front generally will
be a colder and squally W to SW with damaging potential still existing – it
will be bitterly cold with that wind chill for those of you doing any outdoor
work.
A moist
onshore westerly flow will then prevail throughout the day on the 20th
with scattered showers, but more frequent and focused for areas south of about
Kangaroo Island, so generally the SE Districts, especially the Lower SE which
will be embedded further down in the flow. Another cold front will quickly be
moving through in that flow and will chiefly pass below KI however there will
still be some isolated showers north of that for the 21st. However
south of here and again mostly for the Lower SE, showers will increase and
become heavier with the chance of some cold air thunder and small hail once
more. Local heavy falls are possible.
The showers will contract and become much more isolated by the 22nd
with a new ridge moving in across the northern parts of the state. Another cold
front will then be due around the 24th-25th as we continue the
unlocking of the longwave trough. This one will be a steadier system with
either a band of showers or rain across most districts.
Beyond this
the longwave will continue to spin fronts off it, one around the 26th
or so but it seems weaker at this stage and generally aimed at the SE
Districts.
I am however
more interested in a higher amplitude longwave peaking closer to us in early
August. High pressure is likely to re-establish before this however so there
may be a frost window here though brief, I would think.
At this stage
August is a month that should see a good response in the westerly belt as well
as moisture feeds but note systems will be fast moving at times. Overall, the
rainfall from August through till December looks average to above average so no
real changes in the outlook there.
Climate
Drivers:
Now the
Pacific has been in a neutral state for a while now with a lack of forward
movement towards a La Nina with no significant cold-water upwelling. This water
remains just below the surface for the meantime. We still have time for that to
surface and it should do as we move into spring, but odds are firming for a
weak La Nina only. The Humboldt Current whilst present has not really come
along strongly of late, and this is another impeding factor. I’ll watch this
closely as we move into early spring.
The Indian
has slowed it’s movement towards a Negative IOD
however we are already in that range now and have been for two weeks with
–0.42C the latest reading which is negative territory. I did expect a little
resistance back towards positive (more so neutral now) in July and it hasn’t
come yet but look for that before we again dive back negative as we move
towards spring time. We still have plentiful
moisture feeding in off the Indian with yet another NW Cloudband feeding in
ahead of our cold front due on the evening of the 19th. These sorts
of systems have been a feature of late and will continue to do so, especially
now that we have movement from the Longwave Trough (hooray!) which I will touch
on again in the SAM section next.
Figure
1: Current SST anomalies – source Tropical Tidbits
https://www.tropicaltidbits.com/analysis/ocean/cdas-sflux_ssta_global_1.png
So, the SAM
is currently neutral after a strong stint in the positive range earlier in the
month. We now will move into a period where the Longwave Trough will finally
shift east for a more sustained period rather than sit west of WA for so long.
We are likely to also see an expansion phase of the westerly belt due to some
Sudden Stratospheric Warming (SSW) over Antarctica. This has occasionally
happened over the years with the last big event in the spring of 2019 which
enhanced the westerlies greatly causing a drier spring and lots of windy and
strong cold fronts that lacked rainfall due to a positive IOD. Occuring in a
negative year will allow these fronts to tap into tropical moisture and enhance
the potential for strong cut off lows or powerful late winter to spring cold
fronts so this is a thing we need to watch. This SSW event however does not
look to be near the levels of 2019, but we should still see some decent
negative SAM phases in the coming month or so.
The MJO is
largely irrelevant at the moment with a lot of the
main activity pushing into the Atlantic right now, however a weak pulse should
come around potentially in a few weeks but isn’t of much interest to us now.
Districts:
Eyre
Peninsula
Trough
extending from the west early 19th with patchy rain developing
tending areas of rain at times. Fresh to strong N to NW winds extending
throughout early. Rain easing to showers early afternoon before a vigoruous
cold front moves through mid-afternoon with squally showers and strong to gale
force NW to W winds tending colder squally WSW behind. Damaging winds likely
about exposed coasts. Squally showers, some heavy with isolated cold air
thunder and small hail about the Lower Eyre Peninsula are possible in the cold
pool to follow, with shower activity more isolated further north. Showers and
winds easing overnight leaving isolated to scattered lighter showers through 20th,
possibly tending to drizzle periods at times. Isolated showers are possible
right through till the 22nd about Lower Eyre Peninsula in the moist
onshore flow however it should remain fine further north. Another cold front
due 24th with a band of showers or rain, before further onshore
showers follow in a moist W to SW flow. Further follow up front or fronts to
follow around 26th-27th before a clearance ahead of
further frontal activity likely in early August. Rainfall for the period
generally 10-20mm increasing to 20-30mm about Lower Eyre Peninsula where
isolated totals may reach 40mm. Totals decreasing with N/NE extent down to 7-10mm.
Upper North
Trough
extending from the west early 19th with patchy rain developing
tending areas of rain at times. Fresh to strong N to NW winds extending
throughout early. Rain easing to showers later afternoon before a vigoruous
cold front moves through during the evening with squally showers and strong to
gale force NW to W winds tending colder squally WSW behind. Showers isolated
north of Port Augusta. Damaging winds likely about higher peaks. Showers and
winds easing overnight leaving isolated lighter showers through 20th,
possibly tending to drizzle periods at times in the far south. Another cold
front due 24th-25th with a band of showers or rain, before clearing.
Further follow up front or fronts to follow around 26th-27th
however mostly only light showers for the south at this stage. A clearance
ahead of further frontal activity likely in early August. Rainfall for the
period generally 7-12mm increasing to 12-18mm about wetter peaks and elevated
terrain. Totals decreasing with N/NE extent down to 4-7mm.
Lower North
Trough
extending from the west early 19th with patchy rain developing
tending areas of rain at times. Fresh to strong N to NW winds extending
throughout early. Rain easing to showers later afternoon before a vigoruous
cold front moves through during the evening with squally showers and strong to
gale force NW to W winds tending colder squally WSW behind. Damaging winds
likely about higher peaks and elevated terrain. Showers and winds easing
overnight leaving isolated lighter showers through 20th, possibly
tending to drizzle periods at times, especially about western slopes and
elevated terrain. Another cold front due 24th-25th with a band of
showers or rain, before clearing leaving isolated onshore showers, chiefly in
the south. Further follow up front or fronts to follow around 26th-27th
however mostly only light showers at this stage. A clearance ahead of further
frontal activity likely in early August. Rainfall for the period generally
10-20mm increasing to 20-30mm about wetter peaks and elevated terrain. Totals
decreasing with N/NE extent down to 7-10mm.
Yorke
Peninsula
Trough
extending from the west early 19th with patchy rain developing
tending areas of rain at times. Fresh to strong N to NW winds extending
throughout early. Rain easing to showers mid-afternoon before a vigoruous cold
front moves through late afternoon with squally showers and strong to gale
force NW to W winds tending colder squally WSW behind. Damaging winds likely
about exposed coasts, especially around the foot. Squally showers, some heavy
with isolated cold air thunder and small hail about the foot are possible in
the cold pool to follow, with shower activity a little more isolated further
north. Showers and winds easing overnight leaving isolated to scattered lighter
showers through 20th, possibly tending to drizzle periods at times.
Isolated showers are possible right through till the 22nd about the
foot in the moist onshore flow however it should remain fine further north.
Another cold front due 24th-25th with a band of showers or rain,
before further onshore showers follow in a moist W to SW flow. Further follow
up front or fronts to follow around 26th-27th before a
clearance ahead of further frontal activity likely in early August. Rainfall
for the period generally 12-18mm increasing to 18-25mm about the foot where
isolated totals may reach 30mm.
Kangaroo
Island
Trough
extending from the west early 19th with patchy rain developing
tending areas of rain at times. Fresh to strong N to NW winds extending
throughout early. Rain easing to showers mid-afternoon before a vigoruous cold
front moves through late afternoon with squally showers and strong to gale
force NW to W winds tending colder squally WSW behind. Damaging winds likely
about exposed coasts, especially the western end. Squally showers, some heavy
with isolated cold air thunder and small hail are likely in the cold pool to
follow. Showers and winds easing overnight leaving scattered lighter showers
through 20th. Another front or trough to move through on 21st
increasing showers briefly with onshore isolated showers through till 22nd.
Another cold front due 24th-25th with a band of showers or rain,
before further onshore showers follow in a moist W to SW flow. Further follow
up front or fronts to follow around 26th-27th before a
clearance ahead of further frontal activity likely in early August. Rainfall
for the period generally 30-40mm increasing to 50-60mm about the western end.
Totals decreasing towards the eastern end but still 20-30mm likely.
Adelaide
Plains
Trough
extending from the west early 19th with patchy rain developing
tending areas of rain at times. Fresh to strong N to NW winds extending
throughout early. Rain easing to showers mid to late afternoon before a
vigoruous cold front moves through during the evening with squally showers and
strong to gale force NW to W winds tending colder squally WSW behind. Damaging
winds likely about exposed coasts, especially the southern suburbs. Squally
showers, some heavy with isolated cold air thunder and small hail about the
outer southern suburbs are possible in the cold pool to follow, with shower
activity a little more isolated further north beyond Gawler. Showers and winds
easing overnight leaving isolated to scattered lighter showers through 20th,
possibly tending to drizzle periods at times. Isolated showers are possible
right through till the 22nd in the moist onshore flow however it
should remain mostly fine further north. Another cold front due 24th-25th
with a band of showers or rain, before further onshore showers follow in a
moist W to SW flow. Further follow up front or fronts to follow around 26th-27th
before a clearance ahead of further frontal activity likely in early August.
Rainfall for the period generally 25-35mm increasing to 40-45mm about the
foothills. Totals decreasing towards the outer northern plains down to 15-25mm.
Mt.Lofty
Ranges
Trough
extending from the west early 19th with patchy rain developing
tending areas of rain at times. Fresh to strong N to NW winds extending
throughout early. Rain easing to showers mid to late afternoon before a
vigoruous cold front moves through during the evening with squally showers and
strong to gale force NW to W winds tending colder squally WSW behind. Damaging
winds likely about exposed southern coasts and also
higher peaks. Squally showers, some heavy with isolated cold air thunder and
small hail about the southern ranges especially are possible in the cold pool
to follow, with shower activity a little more isolated further north towards
the Northern Ranges near the Barossa and surrounds. Showers and winds easing
overnight leaving isolated to scattered lighter showers through 20th,
possibly tending to drizzle periods at times. Isolated to scattered showers are
possible right through till the 22nd in the moist onshore flow with
orographic effects leading to more frequent precipitation around and just east
of the higher peaks. Another cold front due 24th-25th with a band of
showers or rain, before further onshore showers follow in a moist W to SW flow.
Further follow up front or fronts to follow around 26th-27th
before a clearance ahead of further frontal activity likely in early August.
Rainfall for the period generally 30-40mm increasing to 40-60mm about higher
peaks and known wet spots. Possible isolated 70mm falls. Totals decreasing
towards the Barossa down to 20-30mm.
Riverland/Mallee
Trough
extending from the west early 19th with patchy rain developing
tending areas of rain at times. Fresh to strong N to NW winds extending
throughout early. Rain easing to showers later afternoon before a vigoruous
cold front moves through during the evening with squally showers and strong to
gale force NW to W winds tending colder squally WSW behind. Showers isolated
north of the Southern Mallee and certainly over the Riverland as the rain
shadow dries out the cells. Damaging winds possible. Showers and winds easing
overnight leaving isolated lighter showers through 20th about the Southern and
Western Mallee. Another cold front due 24th-25th with a band of
showers or rain, before clearing. Further follow up front or fronts to follow
around 26th-27th however mostly only light showers for
the southern to Mid-Mallee at this stage. A clearance ahead of further frontal
activity likely in early August. Rainfall for the period generally 6-10mm
increasing to 10-15mm about the more southern to SW Mallee. Totals decreasing
with N/NE extent across the Riverland down to 3-6mm.
Upper SE
Trough
extending from the west early 19th with patchy rain developing
tending areas of rain at times. Fresh to strong N to NW winds extending
throughout early. Rain easing to showers mid to late afternoon before a
vigoruous cold front moves through during the evening with squally showers and
strong to gale force NW to W winds tending colder squally WSW behind. Damaging
winds likely about exposed coasts, especially around the Coorong. Squally
showers, some heavy with isolated cold air thunder and small hail are possible
near the Coorong coast in the cold pool to follow, with shower activity a
little more isolated further east inland. Showers and winds easing by sunrise
leaving isolated to scattered lighter showers through 20th. Isolated
showers tending scattered in the south on the 21st with another
trough or front moving in before becoming isolated again on the 22nd
however it should remain mostly fine further north. Another cold front due 24th-25th
with a band of showers or rain, before further onshore showers follow in a
moist W to SW flow. Further follow up front or fronts to follow around 26th-27th
before a clearance ahead of further frontal activity likely in early August.
Rainfall for the period generally 15-25mm increasing to 25-30mm about the
Coorong coast and in the far south. Totals decreasing towards the N and E down
to around 10-15mm.
Lower SE
Trough
extending from the west early 19th with patchy rain developing
tending areas of rain at times. Fresh to strong N to NW winds extending
throughout early. Rain easing to showers mid to late afternoon before a
vigoruous cold front moves through during the evening with squally showers and
strong to gale force NW to W winds tending colder squally WSW behind. Damaging
winds likely about exposed coasts, especially the SW portions. Squally showers,
some heavy with isolated cold air thunder and small hail are likely in the cold
pool to follow chiefly in the western and southern portions of the district,
with shower activity a little more isolated further east inland. Showers and
winds easing by sunrise leaving isolated to scattered lighter showers through
20th. Showers increasing and becoming heavy again on the 21st
with another trough or front moving in before becoming isolated again on the 22nd.
Another cold front due 24th-25th with a band of showers or rain,
before further onshore showers follow in a moist W to SW flow. Further follow
up front or fronts to follow around 26th-27th before a
clearance ahead of further frontal activity likely in early August. Rainfall
for the period generally 30-40mm increasing to 50-70mm about the SW and
southern coastline. Totals decreasing towards the N and E down to around
20-30mm still.
Western VIC
Trough
extending from the west early 19th with patchy rain developing
tending areas of rain during the day, especially south of the Mallee District.
Fresh to strong N to NW winds extending throughout early. Rain easing to
showers mid evening before a vigoruous cold front moves through during the late
evening with squally showers and strong to gale force NW to W winds tending
colder squally WSW behind. Damaging winds likely about exposed coasts of the SW
District. Squally showers, some heavy with isolated cold air thunder and small
hail are possible over the SW District in the cold pool to follow, with shower
activity a little more isolated further north towards the Wimmera and moreso
Mallee. Showers and winds easing by sunrise leaving isolated to scattered
lighter showers through 20th over the SW District with drier
westerlies keeping showers largely away from areas further north. Isolated
showers tending scattered over the SW District on the 21st with
another trough or front moving in before becoming isolated again on the 22nd
however it should remain mostly fine further north. Showers may be heavy at
times closer to the SA border. Another cold front due 25th with a band of
showers or rain, before further onshore showers follow in a moist W to SW flow.
Further follow up front or fronts to follow around 26th-27th
before a clearance ahead of further frontal activity likely in early August.
Rainfall for the period generally 25-35mm about the SW District increasing to
35-50mm about the coast. Totals decreasing towards the Wimmera down to 15-25mm
and 6-15mm over the Mallee.
Final Notes
·
Strong cold front with damaging winds due
later on 19th. Sheep graziers warning also issued by the BoM
·
More frequent fronts and systems in general
to round out month as Longwave Trough makes another move at us
·
Potential for early August to see an uptick
in this sort of weather as westerly belt expands due to Sudden Stratospheric
Warming
·
La Nina likely to be weak with a weak
Negative IOD through spring
·
Broadly average to above average rainfall to
see out the growing season (including harvest)
Link to
temporary blog website: https://farmweathersa.blogspot.com/
Happy Farming
and Cheers from The Weatherman
*Note –
For interest only, all thoughts are of The Weatherman and may not be reproduced
without my consent.
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