HOW LONG IS THE DRY SPELL HANGING AROUND FOR?

The drier weather across much of the nation is looking anomalous now, usually we get some drying out through February, many areas are usually dry at this time of year which is normal, for southeast inland areas this is the driest time of year.


So we are looking at a fairly dry period for most of the Ag Areas across Australia. This will help to lower the soil moisture and flooding that is ongoing and help create a little bit of give in the overall flood potential moving into the end of the month and beginning of March.


For northern Australia, the dry airmass and lack of rainfall is very much below average, quite frankly, a very large cleanout of moisture. This will lead to build up conditions returning and many areas going dry across northern WA, NT and through Cape York. Even the FNQ coast will look showery with onshore winds, but the intensity of rainfall is likely to be below normal as well.


So for now, a benign week is what many need, but how long does it last.


Moisture Watch Next Week - February 7th-14th 2022

Moisture is very limited through the coming week, mainly confined to the west with moisture shearing off the tropical system over the Indian Ocean that will be moving southwards and this then being drawn into a frontal wave over WA. This may see an increase in cloud and shower/thunderstorm activity out west. The synoptic configuration over the southeast and east of the nation will lead to that moisture becoming inactive under high pressure and also diving southeast and south through SA and VIC. Over the tropics, moisture remains high north of Mulan to Katherine to Normanton. Scattered showers and a few storms with very hit and miss falls to resume this week as the build up returns. Otherwise, below average moisture values are expected this week.

Moisture Watch Next Week - February 14th-21st 2022

The moisture over the northern parts of the nation will return with a Rossby Wave passing over QLD, then through the NT and into northern WA with an uptick of showers and thunderstorms, this may be extended into the sub tropics as well. The return of the SAM to neutral values then positive values, may lead to an increase of showers over the east coast and that moisture moving into the inland of QLD, NSW and VIC with a few showers and storms returning. The west, likely to feel the impacts of the MJO building offshore the northwest coast. Showers and thunderstorms increasing as moisture is fed into the west coast trough. Ridging through Central Australia keeping the bulk of SA dry and parts of southern NT also dry.

CLIMATE DRIVERS

Southern Annular Mode - Neutral trending Negative

The change in the pattern is really down to this driver, the SAM, tending sharply negative during the next week. If this does indeed verify, this will be the first time we have seen negative values for a period since Spring of last year. So it shows you how long the positive phase has dominated for. The event, short lived and values should return to positive values within the 2 weeks, with the 11 members suggesting a brief negative event. That will have implications on the moisture content over southern Australia and introduce a fast flow pattern with fluctuating temperature guide. The weather over the east will be drier, we are now seeing that for the coming week with offshore winds developing and the wet weather over the north of the nation becoming more scattered and below average values expected. Once this driver returns back to neutral to positive values, that is when we see more moisture redevelop, that looks to be in the day 10 range onwards at this time. If you review the climate update that was made on Friday and compare that with the forecast SAM information today, it shows you how volatile the driver is and forecasting this ahead of time is like gambling, so it is important to go off the guide but treat it as such and cross check with the synoptic pattern. You can see there is synergy now between the synoptic and climate drivers so the forecast confidence on it being drier than normal for a while is now, is now higher. Most members do carry the SAM negative in the next week.

Madden/Julian Oscillation Index (MJO)

This has been also fairly inconsistent across modelling, especially the GFS which is what I have been using through this period. The MJO is likely to be weak and stay through the Indian Ocean and try to approach the Australian region, but that idea has now been retarded and likely to see the monsoonal weather contract north and west of the nation for now. This will see a dry signal commence over the north of the nation with the MJO in that phase 3 but if it does move into phase 4 towards the Maritime continent, then more moisture will develop over northern and western parts of the nation. We can see a little bit of evidence of that developing in the outlook period but overall dry for the north means dry for much of the nation at this time of year. Reasonable agreement (green line) keeping the MJO back over the Indian Ocean and leaving it weak.

DATA SETS

18Z GFS Surface Pressure Pattern and Rainfall Distribution - Next 16 Days

You can spot the SAM turning negative this week, with a strong cold front and low pressure system near WA bringing below average temperatures and windy weather. The high pressure ridge also sitting further north and helping to kick the easterly winds further north over the tropical north. The air across much of the nation drier, in line with the negative SAM phase. The MJO also moving into the Indian Ocean will stay there for a good portion of this period meaning reduced rainfall for the coming 10 days over northern Australia. Bottom line areas under significant flooding issues at the moment, you have a chance to dry out and recover before the next wave of rainfall and thundery weather returns into mid to late month.

18z GFS Precipitable Water Anomalies - Next 16 Days

Below average moisture content across the nation means below average rainfall expected for many areas of southern and eastern Australia. That is the response to the above average/record moisture levels and record rainfall for many areas in January. The weather over the tropics anomalously dry for this time of year if this is correct which would result in very low rainfall chances moving towards the southeast and south of the nation. The western interior seeing more moisture courtesy of the MJO moving into the Indian Ocean and progressing eastwards. It takes to the end of the run to see a large slab of moisture return to overrun the dry signal nationally from west to east. That will be a feature to watch over the course of the next week or so.

18z GFS Rainfall Accumulation - Next 16 days - LOW CHANCE

Most aggressive on the drier signal across the nation with the monsoon dissolving and moving on by. Ridging over the nation sitting further north promoting a dry a stable airmass to about day 12-13 of the outlook for many areas. Then we see the monsoon approach the northwest of the nation and that may extend across the remainder of the tropics to end the month and kick off March.

12z CMC Rainfall Accumulation - Next 15 days - LOW CHANCE

Most aggressive in terms of rainfall coverage across the nation with the monsoon trough sitting closer to the north of the nation with enhanced rainfall. The rainfall therefore more generous over the sub tropics and points down the west and east coast. Good agreement on the ridging keeping much of southern and southeast Australia dry and the east coast under onshore winds with light to moderate showers most of the outlook.

12z Euro Rainfall Accumulation - Next 15 days - MODERATE CHANCE

Most likely closer to the post. The 51 members are suggesting more rainfall into the medium term beyond about day 10 at this stage. Northern Australia seeing below average rainfall, the central and southeast/eastern inland also below average rainfall. Some parts of the east seeing near seasonal values and above average rainfall for northwest and western interior. That is a sure sign conditions are shifting and the pattern resetting.

I will have more in my evening state based forecasts coming up after 5pm EDT today, but for the most part, enjoy the quieter weather for this time. It will not last forever!!