MODELS AND RAINFALL - A LOOK AT THE BROADER DATA SETS.

The modelling continues to be of low confidence and you can track the deterministic data across all of the apps out there, but the data is crap and therefore the apps turn crap without human interpretation. I have seen on social media all of the usual places going for widespread severe weather for many locations, but there is no skill in blanketing the risk of flooding and severe storms without careful consideration of all the data sets.


Lets look at the least favourite data sets, the broader ensemble data sets which don't look so pretty but are much more reliable.


There will be a few nervous communities in the east of NSW over the coming week which could see heavy rainfall that may lead to additional minor to moderate riverine flooding. I may introduce flash and riverine flood risk charts for WA coming up in the days ahead but forecast confidence is poor. Also there may be a flood risk for the Top End and through Cape York as well next week.


FORECAST

Riverine Flood Risk - Friday through Tuesday

The catchments are still very wet even though we have seen an absence of rainfall in recent weeks. The rainfall forecast will be moderate to heavy over a number of days and over time, the catchments will respond to this rainfall. Falls of 100-200mm are possible in the coming period in scattered pockets along the extreme coastal fringe and falls of 50mm an hour with thunderstorms are possible in all areas highlighted here. This may trigger minor to moderate flooding to redevelop along the coast. At this stage the amplification of the event is no where near the levels of the previous event but once again, riverine flooding is a significant risk for catchments devastated by the early March event. Remain weather aware through this region.

Flash Flood Risk - Friday through Tuesday

Flash flooding is a significant risk with thunderstorms with the upper level system moving in from Friday if not Saturday, into the moisture and stalled boundary over the north and east of NSW. The two will combine to bring scattered storms, some severe, with heavy rainfall leading to flash flooding a significant risk. From Thursday, there may be thunderstorms along the coastal fringe and streams of heavy showers floating about between Batemans Bay to Yamba that could see some coastal areas net 50mm in a couple of hours. Thunderstorms over the weekend across central, northern and northeast NSW could drop 30-40mm in an hour with the coverage contracting eastwards during the weekend into early next week.

DATA - Refer to the video for further information and it is critical to keep check of the data sets to understand where the next major weather events are emerging from outside of this period. It may be quiet now but I am all about preparation and ensuring that information is shared with you as soon as it is available.


ENSEMBLE DATA

The broader data sets are still signalling the wettest part of the nation will be over the west, through northern and northeast tropical areas and along the east coast, primarily through NSW into the coastal escarpment. Scattered falls may extend inland through central and southeast inland NSW with the chance of light falls getting into northern VIC and possibly central and northwest QLD. The rainfall over WA offers the greater hope of spreading through the southern parts of the nation along wave action that will be building through the outlook period, into early April, representing the shift to a neutral SAM phase and the return of some westerly winds to the south of the nation and high pressure allowed to ridge a little further north. The MJO may also move through quicker and into the Pacific Ocean through the early part of April seeing rainfall easing for northwest WA.


GFS - Rainfall Next 16 Days (median of 35 members) - MODERATE CHANCE

Certainly not deviating from previous updates though has started to introduce more rainfall across the southeast and eastern inland for the second week (medium term), has heavier rainfall over the northeast Top End with the tropical feature and good rainfall lets hope for the west, but those numbers are variable and in association with the remains of Charlotte.

Here is the deterministic to compare and you can see how different that single data set is to the broader data set, why so many people get caught out and don't quite understand the limitations of the models costing them big time. THIS CARRIES A LOW CHANCE!

CMC - Rainfall Next 15 Days (median of 30 members) - MODERATE CHANCE

Starting to increase falls for the west and diving that into the Bight, so no impact on SA if this is right at the time. The models are in good agreement surrounding the rainfall being absent over central areas in the presence of high pressure. Good agreement on the wet spots being over the east and over the north. This model moving into line with the GFS.

EURO - Rainfall Next 15 Days (median of 51 members) - MODERATE CHANCE

Has softened the rainfall for parts of the southeast of NSW where other models are heavier. Has got the heavy rainfall over west of the nation with the moisture coming out of Charlotte and then another system after that. Note the tropical system off the NE Top End. So we are seeing reasonable agreement across the board, now it is just about the small/mesoscale features for each region. Drier over Central Australia through SA.

LONG TERM


CFS - Rainfall Next 6 Weeks - MODERATE CHANCE

A very wet signal continues and this has been rock solid for weeks and continues this into the first week of May, so it could be a pretty wet April for many of us. Stay tuned.

More coming up from 8am EDT.