Weather pattern forecast probabilities for India using the 1200 UTC GEFS-IMD medium-range run on Sun 10 Sep 2023

Research prototype weather pattern forecasts for India

12 UTC GEFS-IMD medium-range run on Sun 10 Sep 2023
Forecasts valid at 12:00 UTC / 17:30 IST

Weather pattern forecast probabilities

Ensemble members are objectively assigned to their closest matching weather pattern definition, using a set of 30 predefined weather patterns. The assignment is achieved by finding the ensemble member and weather pattern pairing with the smallest area-weighted sum of squared differences between their corresponding u- and v-component winds at 850-hPa – this metric is commonly referred to as "distance". Forecast probabilities (as shown in the table below) are then based on the total number of ensemble members assigned to each weather pattern. Click on the "Pattern" links in the first column to view weather pattern definition wind fields at 850-hPa as well as their rainfall climatologies. Click on the "Historical frequency occurrences" links in the last three columns to view a full breakdown for all months in the year. Table cells are colour-coded according to their probability to assist with identifying the most likely weather pattern transitions.

	Mon 11 Sep	Tue 12 Sep	Wed 13 Sep	Thu 14 Sep	Fri 15 Sep	Sat 16 Sep	Sun 17 Sep	Mon 18 Sep	Tue 19 Sep	Wed 20 Sep	Pattern Category	Historical frequency occurrences (August)	Historical frequency occurrences (September)	Historical frequency occurrences (October)
Pattern 1											Retreating Monsoon	0.0%	0.0%	8.4%
Pattern 2											Autumn Dry Period	0.0%	0.0%	0.2%
Pattern 3											Autumn Dry Period	0.0%	0.0%	0.7%
Pattern 4	52%	95%	76%								Break Monsoon	13.0%	2.9%	0.0%
Pattern 5											Western Disturbances	0.0%	0.1%	0.2%
Pattern 6											Retreating Monsoon	0.0%	1.0%	19.4%
Pattern 7										5%	Autumn Dry Period	0.0%	0.1%	0.7%
Pattern 8											Autumn Dry Period	0.0%	0.0%	0.1%
Pattern 9											Autumn Dry Period	0.0%	0.0%	0.8%
Pattern 10			24%	81%			5%				Break Monsoon	10.9%	1.0%	0.0%
Pattern 11											Break Monsoon	14.4%	2.9%	0.0%
Pattern 12											Post-Monsoon	0.2%	1.2%	1.2%
Pattern 13											Post-Monsoon	3.0%	16.3%	4.8%
Pattern 14					38%	57%	57%	57%	86%	81%	Post-Monsoon	9.3%	12.8%	0.2%
Pattern 15											Post-Monsoon	0.2%	9.1%	4.8%
Pattern 16											Autumn Dry Period	0.0%	0.0%	0.1%
Pattern 17							24%	43%	14%	14%	Active Monsoon	11.8%	7.1%	0.3%
Pattern 18											Retreating Monsoon	0.0%	0.6%	11.0%
Pattern 19											Active Monsoon	13.0%	0.5%	0.0%
Pattern 20											Autumn Dry Period	0.0%	0.0%	0.1%
Pattern 21				5%							Active Monsoon	14.1%	2.9%	0.0%
Pattern 22											Post-Monsoon	1.2%	4.6%	1.5%
Pattern 23											Western Disturbances	0.0%	0.2%	0.6%
Pattern 24											Western Disturbances	0.0%	0.3%	0.1%
Pattern 25											Retreating Monsoon	0.0%	3.0%	18.0%
Pattern 26											Monsoon Onset	3.8%	1.4%	0.0%
Pattern 27											Western Disturbances	0.0%	0.2%	0.2%
Pattern 28	48%	5%		14%	62%	43%	14%				Retreating Monsoon	4.8%	21.2%	3.8%
Pattern 29											Retreating Monsoon	0.2%	5.7%	12.2%
Pattern 30											Retreating Monsoon	0.2%	5.0%	10.6%

Cumulative probabilities for each weather pattern category

Probabilities are aggregated for weather patterns with the same descriptions in the table above. For example, probabilities for all weather patterns described as "active monsoon" will be aggregated. This helps identify transitions in the large-scale circulation and is especially useful when there is a lot of ensemble spread across the set of 30 weather patterns.

	Mon 11 Sep	Tue 12 Sep	Wed 13 Sep	Thu 14 Sep	Fri 15 Sep	Sat 16 Sep	Sun 17 Sep	Mon 18 Sep	Tue 19 Sep	Wed 20 Sep
Active Monsoon				5%			24%	43%	14%	14%
Western Disturbances
Monsoon Onset
Post-Monsoon					38%	57%	57%	57%	86%	81%
Autumn Dry Period										5%
Break Monsoon	52%	95%	100%	81%			5%
Retreating Monsoon	48%	5%		14%	62%	43%	14%

Circulation trend indicator tables

Weather patterns have been classified according to their dominant circulation characteristics during four broad seasons: (1) summer monsoon, (2) summer to retreating monsoon, (3) winter dry period and (4) pre-monsoon to monsoon onset. Circulation trends are shown in the four tables below for both the latest and most recent forecasts with daily validity times aligned. This allows for a rapid assessment of forecast consistency over consecutive model runs. In addition, these tables are useful for identifying key transitions in the large-scale circulation.

1. Summer monsoon circulation trend

Please note: This table is intended for use between June and September for identifying active and break phases of the summer monsoon.

	Mon 11 Sep	Tue 12 Sep	Wed 13 Sep	Thu 14 Sep	Fri 15 Sep	Sat 16 Sep	Sun 17 Sep	Mon 18 Sep	Tue 19 Sep	Wed 20 Sep
Latest model run (10/12 UTC)	52%	95%	100%	81%	100%	100%	71%	57%	86%	86%
Previous model run (run -1)	100%	100%	100%	76%	86%	71%	86%	71%	62%
Previous model run (run -2)	52%	95%	76%	76%	100%	95%	86%	81%	86%
Previous model run (run -3)	67%	95%	90%	86%	90%	62%	52%	71%
Previous model run (run -4)	71%	95%	86%	67%	95%	81%	71%	76%
Previous model run (run -5)	90%	100%	90%	52%	48%	76%	76%
Previous model run (run -6)	71%	100%	100%	62%	43%	57%	57%
Previous model run (run -7)	52%	90%	38%	90%	95%	81%
Previous model run (run -8)	67%	100%	86%	--	48%	43%
Previous model run (run -9)	52%	86%	57%	52%	67%

	Weather patterns typically associated with break monsoon tendencies over India are most likely Weather patterns 4, 10 and 11 (break)
	Weather patterns typically associated with no active or break monsoon tendencies over India are most likely Weather patterns not listed above and below
	Weather patterns typically associated with active monsoon tendencies over India are most likely Weather patterns 17, 19 and 21 (active)

2. Summer to retreating monsoon circulation trend

Please note: This table is intended for use between August and November for identifying the start of the retreating monsoon.

	Mon 11 Sep	Tue 12 Sep	Wed 13 Sep	Thu 14 Sep	Fri 15 Sep	Sat 16 Sep	Sun 17 Sep	Mon 18 Sep	Tue 19 Sep	Wed 20 Sep
Latest model run (10/12 UTC)	52%	95%	100%	86%	62%	57%	86%	100%	100%	95%
Previous model run (run -1)	100%	100%	100%	76%	57%	90%	100%	100%	100%
Previous model run (run -2)	62%	95%	81%	71%	76%	71%	100%	100%	100%
Previous model run (run -3)	81%	95%	90%	76%	62%	67%	100%	100%
Previous model run (run -4)	95%	95%	86%	57%	67%	81%	100%	100%
Previous model run (run -5)	100%	100%	95%	86%	95%	100%	100%
Previous model run (run -6)	100%	100%	100%	67%	71%	100%	100%
Previous model run (run -7)	100%	95%	71%	100%	100%	100%
Previous model run (run -8)	100%	100%	95%	95%	100%	100%
Previous model run (run -9)	100%	95%	86%	100%	100%

	Weather patterns typically associated with summer monsoon tendencies over India are most likely Weather patterns 12, 13, 15, 15 and 22 (pre/post summer monsoon); 26 (onset); 17, 19 and 21 (active); 4, 10 and 11 (break)
	Weather patterns typically associated with no summer or retreating monsoon tendencies over India are most likely Weather patterns not listed above and below
	Weather patterns typically associated with retreating monsoon tendencies over India are most likely Weather patterns 1, 6, 18, 25, 28, 29 and 30 (retreating)

3. Winter circulation trend

Please note: This table is intended for use between December and May for identifying periods most susceptible to western disturbances during the winter dry period.

	Mon 11 Sep	Tue 12 Sep	Wed 13 Sep	Thu 14 Sep	Fri 15 Sep	Sat 16 Sep	Sun 17 Sep	Mon 18 Sep	Tue 19 Sep	Wed 20 Sep
Latest model run (10/12 UTC)	100%	100%	100%	100%	100%	100%	100%	100%	100%	95%
Previous model run (run -1)	100%	100%	100%	100%	100%	100%	100%	100%	100%
Previous model run (run -2)	100%	100%	100%	100%	100%	100%	100%	100%	100%
Previous model run (run -3)	100%	100%	100%	100%	100%	100%	100%	100%
Previous model run (run -4)	100%	100%	100%	100%	100%	100%	100%	100%
Previous model run (run -5)	100%	100%	100%	100%	100%	100%	100%
Previous model run (run -6)	100%	100%	100%	100%	100%	100%	100%
Previous model run (run -7)	100%	100%	100%	100%	100%	100%
Previous model run (run -8)	100%	100%	100%	100%	100%	100%
Previous model run (run -9)	100%	100%	100%	100%	100%

	Weather patterns typically associated with contrywide dry period tendencies over India are most likely Weather patterns 2, 3, 7, 8, 9, 16 and 20 (countrywide winter dry period)
	Weather patterns typically associated with no dry period or western disturbance tendencies over India are most likely Weather patterns not listed above and below
	Weather patterns typically associated with western disturbance tendencies over India are most likely Weather patterns 5, 23, 24 and 27 (western disturbances)

4. Spring to summer monsoon circulation trend

Please note: This table is intended for use between May and July for identifying monsoon onset.

	Mon 11 Sep	Tue 12 Sep	Wed 13 Sep	Thu 14 Sep	Fri 15 Sep	Sat 16 Sep	Sun 17 Sep	Mon 18 Sep	Tue 19 Sep	Wed 20 Sep
Latest model run (10/12 UTC)	52%	95%	100%	86%	62%	57%	57%	57%	86%	81%
Previous model run (run -1)	100%	100%	100%	76%	57%	71%	86%	76%	62%
Previous model run (run -2)	62%	95%	76%	71%	76%	67%	86%	81%	86%
Previous model run (run -3)	81%	95%	90%	76%	62%	38%	52%	71%
Previous model run (run -4)	95%	95%	86%	57%	67%	62%	71%	76%
Previous model run (run -5)	100%	100%	90%	48%	52%	76%	76%
Previous model run (run -6)	100%	100%	100%	62%	71%	81%	57%
Previous model run (run -7)	100%	95%	71%	95%	100%	90%
Previous model run (run -8)	100%	100%	95%	86%	86%	62%
Previous model run (run -9)	100%	90%	--	57%	76%

	Weather patterns typically associated with pre-monsoon tendencies over India are most likely Weather patterns 12, 13, 14, 15 and 22 (pre-monsoon)
	Weather patterns typically associated with no pre- or summer monsoon tendencies over India are most likely Weather patterns not listed above and below
	Weather patterns typically associated with summer monsoon tendencies over India are most likely Weather patterns 26 (onset); 17, 19 and 21 (active); 4, 10 and 11 (break)

Weather regime stacked probabilities

Weather pattern probabilities are aggregated according to their common regime group and presented as stacked probabilities. Regime bars are colour-coded based on their dominant circulation characteristics. Here, orange indicates winter types, light blue indicates pre- and post-monsoon / monsoon onset types, dark blue indicates the main summer monsoon types (active / break) and green indicates the retreating monsoon type. Hatching is used to distinguish between sub-types within a given colour. The regime ordering always remains the same to allow for an easy comparison with forecasts from previous runs and from different models. These plots complement the circulation trend indicator tables by enabling a quick assessment of any large-scale circulation changes and can be compared with previous runs to interpret forecast consistency. Regime descriptions in the plot are for guidance only; please refer to the top-level weather pattern forecasts for more detail.

Forecast confidence index

The forecast confidence index plot allows for an objective assessment of ensemble spread across the set of 30 weather patterns, by comparing the forecast confidence index from the latest run to that from a number of historical runs (as defined in the plot title). A score of 0 means that all members are equally distributed across all weather patterns, whereas a score of 1 means that all members are assigned to the same weather pattern. Green shading highlights days where ensemble spread is less than normal and red shading highlights days where ensemble spread is more than normal. Note that the forecast confidence index is not a measure of forecast skill.

Underlying forecast data (CSV files)

CSV files are available for download which provide the underlying data used in the generation of these forecasts. This includes the weather pattern assignments for each ensemble member and the distances (as a grid-point average area-weighted sum of squared differences) between each ensemble member and its closest matching weather pattern definition, using u- and v-component winds at 850-hPa between both fields. CSV files contain one row for each forecast day. The first column gives the forecast validity date and time in the format YYYYMMDDHH. The following columns then give the values (pattern assignments or distances) for each ensemble member, with the control member values given first followed in order by all other members.

Ensemble member pattern assignments
(CSV file)

Ensemble member pattern distances
(CSV file)

Page created at 01:56:30 (India local time) on Mon 11 Sep 2023

Data provided by the India Meteorological Department, MoES, GoI Colloboration with Met Office Under WCSSP Project