Thread by @althecat

#ExtremeWeather #DesertRain update.

Six days later this Great Sahara Desert rain event is not weakening much yet it seems.

That said. The latest detailed forecast does show it weakening beyond the 13th of August though. By then the event would have run for two weeks. The… https://t.co/tnSHpLo8Wl https://t.co/6SnhemLCkytwitter.com/i/web/status/1…

https://twitter.com/althecat/status/1686069720380817413

That said the underlying cause - the high pressure circulation over west of Kerela India is still pumping.

And the atmospheric water vapour picture (Precipitable Water - i.e. atmospheric water vapour that could produce rain) remains spectacular.

Here'e the latest IWVT transportation picture again 16 days GFS3 Model. The complexity of the sources of water vapour involved in this process (due to meandering jetstream and other altitude transportation) and their persistence remains fairly consistent with what we saw in the… https://t.co/AeEffBE5xKtwitter.com/i/web/status/1…

In these plots we can see what the models are currently seeing at different altitudes in terms of wind. This is zero hour data - i.e. the starting point for the detetministic model simulation.
1. 250 Hpa (high jetstream)
2. 500 Hpa (low jetstream)
3. 850 Hpa (15kms top of most… https://t.co/kVWg988uE7twitter.com/i/web/status/1…

^^ This data suggests to me that the main water flows responsible are lower in the atmosphere. But I could be wrong about this as I am not that familiar with reading these plots. There seems to be relativel few strong winds at higher altitudes though.

This plot of MLSP (air… https://t.co/6KC9KMJVeGtwitter.com/i/web/status/1…

Total Precipitation anomaly in the forecast
1. GFS3 August 2 at 384 hours.
2. GFS3 August 4 (latest data is not available for some reason)
3. GEFS Northern Hemisphere 7 day % of normal (Africa is on the RHS)
4. GEFS Northern Hemisphere Total % of Normal (over 16 days) The blue… https://t.co/IjHBYelCmWtwitter.com/i/web/status/1…

This view of the GEFS (ensemble) forecast [i.e. the mean of of a range of different model runs] shows the rain up to around 27o North across all of the Sahara that is anomalous. (look at RHS....)

This images crops out the relevant portion of the image in the previous tweet. The bottim dotted line that arcs across the image shows the normal extent of rain. Everything north of that is anomalous.

Here's the latest GFS3 16 day total anomaly forecast. The big blue blob shows the extent of the anomaly in the Sahara. It looks like it covers more than 50% of the total Sahara Desert landmass.

Using the above blue anomaly area as a guide the total size of the area which is forecast to receive #DesertRainfall over the coming 16 days anomalously compared to the climate reference sample covers roughly 5,380,000 km2, an area half way between the size of India and… https://t.co/Rfb7vc97zstwitter.com/i/web/status/1…

/ends

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