Grand Beach
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grand Beach clear sky chart from 2005-11-06 to 2024-02-05.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	12% 9% 4 8% 6% 4 5% 5% 6% 7% 34%	77693
	Night	11% 10% 5% 9% 7% 4 6% 5% 6% 7% 31%	81203
Transparency	Day	49% 5% 14% 23% 8% 1	77375
	Night	53% 5% 14% 20% 8% 1	81054
Seeing	Day	14% 4 20% 34% 22% 6%	15146
	Night	16% 4 25% 36% 17% 3	25266

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	6% 15% 8% 12% 10% 7% 10% 6% 5% 6% 16%	2218
	11th to 20th	Day	5% 10% 5% 15% 14% 9% 9% 7% 8% 6% 11%	2220
	21st to end	Day	7% 17% 9% 16% 9% 5% 6% 5% 6% 5% 14%	2698
February	1st to 10th	Day	8% 11% 6% 9% 8% 5% 10% 9% 7% 9% 20%	1576
	11th to 20th	Day	8% 10% 5% 9% 8% 5% 7% 7% 6% 10% 25%	1574
	21st to end	Day	6% 10% 6% 11% 8% 5% 7% 6% 8% 7% 26%	1369
March	1st to 10th	Day	11% 12% 5% 11% 7% 4 6% 6% 6% 6% 25%	1852
	11th to 20th	Day	9% 9% 5% 8% 7% 4 5% 5% 6% 7% 34%	1980
	21st to end	Day	11% 10% 4 8% 7% 4 5% 5% 5% 6% 35%	2178
April	1st to 10th	Day	11% 9% 4 8% 5% 3 5% 5% 6% 7% 39%	2200
	11th to 20th	Day	11% 8% 3 5% 6% 3 6% 5% 5% 7% 40%	2312
	21st to end	Day	13% 7% 3 6% 6% 4 5% 6% 6% 7% 37%	2340
May	1st to 10th	Day	14% 7% 3 6% 4 3 3 4 5% 7% 43%	2459
	11th to 20th	Day	16% 7% 3 5% 5% 3 4 5% 5% 8% 41%	2605
	21st to end	Day	18% 7% 3 5% 5% 3 5% 5% 5% 7% 38%	2918
June	1st to 10th	Day	16% 6% 3 6% 5% 3 5% 6% 6% 7% 39%	2700
	11th to 20th	Day	16% 6% 3 5% 5% 3 5% 6% 6% 8% 37%	2700
	21st to end	Day	13% 6% 2 6% 6% 3 5% 5% 7% 9% 38%	2700
July	1st to 10th	Day	8% 4 2 4 4 3 4 5% 7% 9% 50%	2700
	11th to 20th	Day	11% 4 2 4 5% 2 5% 5% 7% 9% 46%	2700
	21st to end	Day	9% 4 2 4 4 3 5% 5% 5% 8% 50%	2939
August	1st to 10th	Day	9% 4 3 4 5% 3 5% 4 7% 9% 47%	2458
	11th to 20th	Day	11% 5% 2 5% 4 3 5% 4 6% 7% 48%	2301
	21st to end	Day	13% 6% 2 5% 5% 3 4 5% 5% 8% 45%	2574
September	1st to 10th	Day	11% 7% 2 5% 4 3 4 4 5% 8% 47%	2246
	11th to 20th	Day	16% 7% 3 6% 6% 4 4 5% 6% 8% 35%	1991
	21st to end	Day	16% 8% 2 5% 5% 3 4 4 6% 8% 39%	1980
October	1st to 10th	Day	21% 11% 3 7% 5% 3 4 4 4 7% 30%	1814
	11th to 20th	Day	16% 14% 5% 7% 6% 3 4 5% 6% 5% 28%	1775
	21st to end	Day	17% 17% 4 10% 7% 4 5% 5% 5% 7% 19%	1766
November	1st to 10th	Day	17% 14% 6% 12% 8% 3 4 4 4 6% 22%	1487
	11th to 20th	Day	11% 16% 7% 14% 12% 5% 4 4 4 4 19%	1520
	21st to end	Day	12% 14% 7% 12% 11% 5% 5% 5% 4 6% 19%	1392
December	1st to 10th	Day	9% 13% 7% 15% 12% 6% 6% 7% 5% 6% 13%	1330
	11th to 20th	Day	9% 15% 7% 11% 8% 5% 7% 6% 6% 7% 19%	1679
	21st to end	Day	9% 12% 5% 10% 8% 5% 7% 6% 8% 9% 21%	2442
January	1st to 10th	Night	5% 13% 7% 12% 9% 7% 10% 7% 6% 6% 18%	4737
	11th to 20th	Night	5% 12% 6% 13% 15% 9% 9% 7% 5% 5% 13%	4750
	21st to end	Night	8% 18% 7% 13% 8% 5% 6% 6% 6% 5% 18%	4965
February	1st to 10th	Night	7% 13% 4 9% 8% 5% 7% 7% 6% 5% 28%	2479
	11th to 20th	Night	8% 10% 4 8% 6% 3 6% 7% 7% 9% 32%	2273
	21st to end	Night	6% 10% 6% 11% 7% 5% 6% 6% 5% 7% 32%	1902
March	1st to 10th	Night	9% 11% 6% 10% 7% 4 5% 6% 7% 6% 30%	2095
	11th to 20th	Night	8% 8% 3 7% 6% 3 5% 4 5% 7% 42%	1979
	21st to end	Night	13% 11% 4 7% 5% 3 4 4 4 7% 37%	2178
April	1st to 10th	Night	12% 8% 3 6% 5% 3 5% 5% 5% 7% 41%	1756
	11th to 20th	Night	12% 9% 4 7% 7% 3 5% 5% 6% 7% 37%	1599
	21st to end	Night	8% 8% 4 8% 7% 4 7% 5% 6% 6% 37%	1620
May	1st to 10th	Night	17% 8% 3 6% 5% 3 5% 5% 5% 6% 38%	1500
	11th to 20th	Night	16% 5% 3 5% 6% 3 5% 3 5% 8% 41%	1288
	21st to end	Night	18% 7% 2 4 4 3 4 5% 7% 6% 39%	1358
June	1st to 10th	Night	14% 7% 4 6% 6% 3 5% 4 6% 9% 36%	1260
	11th to 20th	Night	15% 5% 3 4 5% 4 5% 4 7% 7% 41%	1260
	21st to end	Night	13% 4 2 5% 4 4 5% 5% 7% 13% 40%	1260
July	1st to 10th	Night	8% 2 2 3 2 3 3 6% 7% 9% 55%	1260
	11th to 20th	Night	10% 4 2 3 4 2 5% 5% 8% 9% 49%	1260
	21st to end	Night	8% 4 2 4 5% 2 4 4 6% 8% 55%	1379
August	1st to 10th	Night	8% 4 1 5% 5% 3 5% 4 4 8% 53%	1478
	11th to 20th	Night	10% 3 2 5% 5% 2 3 6% 7% 8% 51%	1600
	21st to end	Night	13% 5% 2 4 4 3 4 4 5% 7% 48%	1782
September	1st to 10th	Night	11% 6% 2 6% 5% 3 4 4 6% 7% 47%	1714
	11th to 20th	Night	15% 6% 3 6% 5% 3 4 5% 5% 7% 42%	1966
	21st to end	Night	17% 6% 3 5% 5% 3 4 4 6% 8% 38%	1980
October	1st to 10th	Night	18% 10% 4 5% 5% 3 4 4 5% 7% 34%	2128
	11th to 20th	Night	20% 12% 5% 7% 5% 3 4 4 4 6% 30%	2182
	21st to end	Night	18% 15% 5% 9% 6% 4 4 4 5% 6% 25%	2588
November	1st to 10th	Night	15% 16% 6% 10% 8% 4 4 4 5% 4 24%	2591
	11th to 20th	Night	12% 17% 9% 14% 9% 3 4 3 4 5% 20%	2660
	21st to end	Night	14% 15% 7% 13% 11% 5% 4 5% 4 5% 18%	2783
December	1st to 10th	Night	8% 12% 6% 14% 12% 7% 7% 5% 6% 5% 19%	2850
	11th to 20th	Night	8% 15% 7% 11% 8% 5% 6% 6% 6% 6% 21%	3518
	21st to end	Night	8% 9% 5% 11% 9% 6% 7% 7% 7% 6% 24%	5225

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	67% 5% 12% 13% 3	2219
	11th to 20th	Day	71% 3 11% 11% 3	2220
	21st to end	Day	73% 4 7% 12% 5%	2698
February	1st to 10th	Day	58% 6% 13% 15% 8% 1	1576
	11th to 20th	Day	54% 5% 12% 20% 9%	1583
	21st to end	Day	55% 5% 12% 21% 7%	1369
March	1st to 10th	Day	59% 4 12% 17% 7%	1854
	11th to 20th	Day	49% 6% 15% 22% 7%	1980
	21st to end	Day	49% 6% 15% 21% 8% 1	2178
April	1st to 10th	Day	47% 3 13% 25% 11% 1	2200
	11th to 20th	Day	44% 5% 10% 24% 16% 2	2312
	21st to end	Day	45% 5% 15% 25% 9% 1	2340
May	1st to 10th	Day	43% 4 11% 26% 15% 1	2459
	11th to 20th	Day	44% 4 10% 26% 15% 2	2609
	21st to end	Day	47% 6% 10% 22% 14% 1	2918
June	1st to 10th	Day	45% 5% 13% 25% 11% 1	2700
	11th to 20th	Day	45% 8% 14% 21% 12% 1	2700
	21st to end	Day	42% 7% 17% 26% 7% 1	2700
July	1st to 10th	Day	30% 5% 17% 34% 12% 1	2626
	11th to 20th	Day	34% 6% 19% 32% 9% 1	2619
	21st to end	Day	34% 6% 19% 31% 10%	2776
August	1st to 10th	Day	33% 6% 20% 33% 7%	2441
	11th to 20th	Day	36% 6% 20% 33% 5%	2301
	21st to end	Day	38% 5% 19% 31% 7%	2574
September	1st to 10th	Day	37% 6% 17% 32% 7% 1	2246
	11th to 20th	Day	47% 6% 18% 26% 3	1991
	21st to end	Day	44% 4 17% 29% 6%	1980
October	1st to 10th	Day	55% 5% 16% 19% 5%	1814
	11th to 20th	Day	55% 5% 15% 21% 4	1775
	21st to end	Day	64% 5% 16% 12% 2	1766
November	1st to 10th	Day	63% 3 14% 15% 3 1	1487
	11th to 20th	Day	66% 6% 12% 13% 3	1520
	21st to end	Day	67% 3 17% 11% 2	1392
December	1st to 10th	Day	71% 5% 11% 11% 2	1330
	11th to 20th	Day	62% 5% 17% 12% 4	1680
	21st to end	Day	60% 6% 10% 18% 5%	2442
January	1st to 10th	Night	66% 5% 12% 13% 4	4737
	11th to 20th	Night	72% 4 8% 14% 2	4750
	21st to end	Night	67% 4 12% 13% 4	4965
February	1st to 10th	Night	54% 5% 13% 18% 9% 1	2479
	11th to 20th	Night	45% 6% 18% 22% 10%	2274
	21st to end	Night	53% 4 11% 21% 11%	1902
March	1st to 10th	Night	52% 5% 12% 19% 10% 1	2106
	11th to 20th	Night	41% 5% 14% 28% 10% 2	1980
	21st to end	Night	48% 4 12% 22% 12% 2	2178
April	1st to 10th	Night	42% 4 10% 25% 17% 3	1756
	11th to 20th	Night	45% 4 9% 22% 15% 4	1599
	21st to end	Night	45% 5% 10% 24% 14% 1	1620
May	1st to 10th	Night	46% 4 10% 25% 14%	1500
	11th to 20th	Night	42% 4 11% 27% 14% 2	1289
	21st to end	Night	44% 6% 12% 19% 18% 2	1358
June	1st to 10th	Night	43% 6% 15% 25% 10% 1	1260
	11th to 20th	Night	42% 5% 14% 23% 15% 2	1260
	21st to end	Night	35% 7% 21% 28% 8% 1	1260
July	1st to 10th	Night	23% 6% 15% 40% 15% 1	1225
	11th to 20th	Night	29% 6% 21% 31% 12% 2	1218
	21st to end	Night	29% 5% 16% 38% 12%	1302
August	1st to 10th	Night	30% 5% 18% 37% 11% 1	1471
	11th to 20th	Night	30% 6% 24% 30% 10%	1600
	21st to end	Night	35% 5% 18% 31% 10% 1	1782
September	1st to 10th	Night	36% 5% 18% 30% 11%	1714
	11th to 20th	Night	40% 5% 20% 24% 9% 1	1966
	21st to end	Night	44% 5% 16% 28% 7%	1980
October	1st to 10th	Night	49% 4 17% 21% 8%	2128
	11th to 20th	Night	55% 4 14% 22% 5%	2182
	21st to end	Night	60% 4 15% 17% 3	2588
November	1st to 10th	Night	63% 5% 14% 13% 4	2591
	11th to 20th	Night	67% 4 13% 11% 4	2660
	21st to end	Night	70% 4 13% 10% 3	2783
December	1st to 10th	Night	67% 4 16% 10% 3	2850
	11th to 20th	Night	61% 4 15% 14% 6%	3516
	21st to end	Night	57% 6% 11% 19% 7%	5225

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	10% 1 33% 36% 16% 4	270
	11th to 20th	Day	10% 4 22% 42% 20% 2	270
	21st to end	Day	17% 3 21% 37% 18% 4	297
February	1st to 10th	Day	12% 5% 25% 40% 13% 4	252
	11th to 20th	Day	12% 6% 28% 31% 17% 7%	240
	21st to end	Day	6% 2 24% 42% 26% 1	198
March	1st to 10th	Day	12% 3 21% 33% 27% 5%	240
	11th to 20th	Day	12% 3 22% 37% 23% 5%	240
	21st to end	Day	14% 3 21% 33% 23% 6%	264
April	1st to 10th	Day	13% 4 19% 42% 19% 4	460
	11th to 20th	Day	14% 4 21% 34% 22% 5%	590
	21st to end	Day	15% 4 18% 36% 23% 5%	600
May	1st to 10th	Day	12% 3 21% 35% 24% 4	603
	11th to 20th	Day	17% 4 15% 32% 25% 7%	625
	21st to end	Day	17% 5% 15% 28% 29% 6%	679
June	1st to 10th	Day	16% 4 17% 33% 23% 8%	630
	11th to 20th	Day	13% 4 22% 32% 24% 4	630
	21st to end	Day	12% 3 14% 33% 28% 9%	630
July	1st to 10th	Day	8% 3 18% 34% 28% 9%	621
	11th to 20th	Day	12% 4 17% 33% 26% 8%	618
	21st to end	Day	8% 3 15% 34% 31% 10%	684
August	1st to 10th	Day	9% 2 20% 32% 27% 11%	626
	11th to 20th	Day	11% 3 14% 33% 27% 12%	615
	21st to end	Day	13% 5% 18% 31% 26% 7%	693
September	1st to 10th	Day	11% 4 26% 34% 22% 4	536
	11th to 20th	Day	16% 9% 19% 37% 16% 4	281
	21st to end	Day	20% 6% 22% 33% 18% 1	270
October	1st to 10th	Day	22% 6% 22% 30% 17% 4	270
	11th to 20th	Day	17% 9% 21% 39% 13% 1	270
	21st to end	Day	29% 4 26% 28% 10% 3	297
November	1st to 10th	Day	21% 5% 26% 32% 14% 1	270
	11th to 20th	Day	16% 7% 35% 30% 11% 2	270
	21st to end	Day	19% 9% 30% 36% 6%	270
December	1st to 10th	Day	12% 4 28% 37% 16% 4	270
	11th to 20th	Day	15% 6% 33% 33% 11% 2	270
	21st to end	Day	11% 5% 22% 39% 20% 4	297
January	1st to 10th	Night	13% 4 29% 35% 17% 2	950
	11th to 20th	Night	14% 3 27% 40% 14% 2	950
	21st to end	Night	15% 4 25% 39% 16% 1	1045
February	1st to 10th	Night	12% 4 24% 40% 18% 2	923
	11th to 20th	Night	11% 3 24% 37% 20% 4	879
	21st to end	Night	10% 2 28% 36% 21% 2	718
March	1st to 10th	Night	12% 4 24% 37% 21% 3	666
	11th to 20th	Night	12% 2 30% 40% 14% 2	540
	21st to end	Night	16% 4 25% 33% 18% 5%	594
April	1st to 10th	Night	16% 2 24% 41% 14% 3	540
	11th to 20th	Night	15% 3 23% 37% 20% 2	533
	21st to end	Night	11% 4 22% 44% 17% 2	540
May	1st to 10th	Night	19% 3 23% 38% 14% 2	540
	11th to 20th	Night	16% 3 19% 37% 22% 4	531
	21st to end	Night	20% 2 19% 38% 19% 2	584
June	1st to 10th	Night	18% 1 21% 33% 24% 3	540
	11th to 20th	Night	16% 4 21% 34% 23% 2	540
	21st to end	Night	13% 4 12% 38% 30% 4	540
July	1st to 10th	Night	7% 2 17% 41% 29% 4	525
	11th to 20th	Night	10% 2 19% 38% 25% 5%	522
	21st to end	Night	10% 2 15% 36% 30% 6%	591
August	1st to 10th	Night	11% 1 17% 41% 26% 4	537
	11th to 20th	Night	10% 2 17% 37% 28% 7%	534
	21st to end	Night	14% 4 19% 36% 25% 3	594
September	1st to 10th	Night	16% 3 24% 36% 17% 4	540
	11th to 20th	Night	17% 5% 23% 39% 14% 2	540
	21st to end	Night	18% 5% 28% 32% 15% 2	540
October	1st to 10th	Night	24% 7% 28% 29% 11% 1	688
	11th to 20th	Night	25% 8% 24% 31% 11% 1	742
	21st to end	Night	27% 9% 24% 29% 9% 1	990
November	1st to 10th	Night	22% 7% 31% 26% 12% 1	925
	11th to 20th	Night	20% 7% 31% 31% 8% 3	950
	21st to end	Night	20% 5% 35% 32% 7% 1	950
December	1st to 10th	Night	12% 4 28% 37% 16% 3	950
	11th to 20th	Night	16% 5% 33% 34% 11% 1	950
	21st to end	Night	16% 4 30% 32% 16% 2	1045

Page generated at 2024-02-02 04:20:27. Version ac07

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