NH Spring/SH Fall 2021 Discussion Thread

Large fire has broken out on Marsden Moor, between Manchester and Leeds. A testament to how dry the past month has been.

Mostly cloudy with sunny spells, max 7C in Riga. Europe:

Aussies have a different perspective on a 'cold' winter....
"How many very cool days can we expect this winter in Melbourne?"
( source: Weatherzone )
As the temperature drops and Victorians begin to turn on their gas heating, many in the National Electricity Market (NEM) are wondering what the gas demands this winter will be?

Cool blasts and high gas demand are primarily brought about by Antarctic southerly winds behind cold fronts that sweep across southern Australia.

So, can we predict the number of cold fronts or cool spells that will hit southern Australia this winter?

Not exactly, climate drivers such as La Nina may indicate fewer cold fronts than average over the months. However, La Nina has finished and is not expected to impact our winter. There are no major indications of cooler or warmer winter this year, due to the lack of climate drivers influencing our weather. Most models are showing a normal to slightly above normal temperatures this winter across the NEM.

However, the Southern Annular Mode (SAM) is a great indication of above or below normal temperatures and wind power in the next 14 days. The SAM refers to the north or south movement of the westerly wind belt or cold fronts that move across southern Australia. SAM three phases, neutral, positive, and negative, each event lasts for one to two weeks, however it oscillates randomly, and longer periods can occur (SAM observations- black line in figure 1).

Positive SAM means cold fronts pass further south than normal, with high pressure systems dominating our weather. This promotes lighter winds, warmer daytime temperatures, and stable weather. However, under the influence of high pressure, skies are clearer, which brings cooler overnight temperatures.

Negative SAM is the phase to watch this winter in terms of gas demand, as it shifts cold fronts further north than normal. An increase in the number of cold fronts hitting southern Australia this winter will bring cooler daytime temperatures, high wind power and increased cloud cover and precipitation.

The SAM is forecast to be neutral during the next two weeks, with cold fronts passing through southern Australia at the usual position (blue line in figure 1).

During this winter, SAM is expected to oscillate between each phase. There are some indications that negative SAM may dominate some of August, bringing increased wind power and cooler temperatures overall for the month.

How many very cool days can we expect this winter in Melbourne?

Our models here at Weatherzone are forecasting around 11 very cool days (Maximum temperature below 12C) this winter in Melbourne, which is one day below average (figure 2). While this year's cool days forecast is near normal, we are forecasting more cool days (Max temperature below 12C) than the previous 3 winters, which may come as a shock to Victorians (figure 2).

The previous three winters were all affected by climate drivers with El Nino conditions observed in 2018, a positive Indian Ocean Dipole in 2019 and the beginning of La Nina last year, 2020 (figure 2).

Weatherzone’s model OptiCast can predict temperatures, including the risk of cool spells up to 2 weeks out. In addition to this, long term seasonal forecasting can indicate temperature, pressure, wind, cloud, rain, and snowfall trends up to 6 months out.

Really highlights just how pathetic Melbourne is…can't even go more than 2° C below the avg winter max on more than 10 days a year. FFS what a shit heap of a climate.

Amen to that. It's been boring shit here too aside from the nice cold snap in early February.


Very warm overnight low here, didn't drop below 73 F (22.8 C) and we're headed up to 82 F (27.8 C) with a small chance of sprinkles today. Extremely exciting weather. The weather forecast has me jumping out of my seat as well.





At least some rain showers are starting to show up in the forecast, I guess.

Germany may be headed for its coldest April month in 30 years.



google translate from the linked article.

In the past few years, April had already brought plenty of spring warmth in Germany - this year is different. Even if the final balance of the German Weather Service (DWD) is not due until the end of the week, it is already becoming apparent that the month is likely to be below the temperature norm of the long-term average and could turn out to be the coldest April month in the last 30 years.

Large diurnals lately in central France, with some days both approaching the 0°C and 25°C marks. For example here in Nevers, on the shores of the Loire. Note the close to freezing average low (among large stations, Charleville in the Northeast will average freezing lows this month).

www.infoclimat.fr/climatologie-mensuelle/07260/avril/2021/-staname-.html


Awful sight. Rh drops in the 20s every day now, with temps nearing 20°C coupled with negative dews. It's been below 30% for 8 straight hours this afternoon for example. This plus the wind drops the water content of the superficial layers of the soil fast now.



Mean humidity:




Evapotranspiration reaches summerlike levels:

Disgusting. Hopefully June to August is a furnace.

Dang, Helsinki centre recorded a low of -0.4C today, and it was their first freeze in April, the last being on 27 March. The station has never failed not to record a freeze in the month of April, and sadly didn't manage it this year either. Sad!